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メイン Arcturus Editorial Board The Great Book of Questions and Answers: Over 1000 Questions and Answers
Arcturus Editorial Board The Great Book of Questions and Answers: Over 1000 Questions and AnswersArcturus Editorial Board
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Verizon Wireless is proud to sponsor this ebook for Gigapedia.org Verizon Wireless proudly sponsors free books for free minds. Click here to learn more about CAST This ebook licensed to Gigapedia.org . Unauthorized reproduction or distribution of this ebook is illegal. GrBigBk_Q_A 001-003 Foul 21/5/07 12:11 pm Page 1 GrBigBk_Q_A 001-003 Foul 21/5/07 12:11 pm Page 2 Arcturus Publishing Limited 26/27 Bickels Yard 151–153 Bermondsey Street London SE1 3HA Published in association with foulsham W. Foulsham & Co. Ltd, The Publishing House, Bennetts Close, Cippenham, Slough, Berkshire SL1 5AP, England ISBN: 978-0-572-03335-4 This edition printed in 2007 Copyright © 2007 Arcturus Publishing Limited All rights reserved The Copyright Act prohibits (subject to certain very limited exceptions) the making of copies of any copyright work or of a substantial part of such a work, including the making of copies by photocopying or similar process. Written permission to make a copy or copies must therefore normally be obtained from the publisher in advance. It is advisable also to consult the publisher if in any doubt as to the legality of any copying which is to be undertaken. British Library Cataloguing-in-Publication Data: a catalogue record for this book is available from the British Library Printed in China Created by: Q2A Media Editors: Ella Fern and Fiona Tulloch Cover design: Q2A Media/Steve Flight GrBigBk_Q_A 001-003 Foul 21/5/07 12:11 pm Page 3 GrBigBk_Q_A 004-005 Content.qxd 21/5/07 12:10 pm Page 4 Contents Universe Galaxies Stars The Sun The Planets The Hot Planet The Earth's Twin The Red Planet The King of Planets The Last Planets Dwarf Planets The Moon Comets and Asteroids Humans in Space Planet Earth Earth's Atmosphere Seasons and Climate Mountains, Valleys and Caves Other Landforms Oceans Volcanoes Earthquakes and Tsunamis Hurricanes and Tornadoes The Living Planet Monkeys Apes Big cats Bears Canines Elephants 6-25 6 8 10 12 14 15 16 17 18 19 20 22 24 26-41 26 28 30 32 34 36 38 40 42-101 42 44 46 48 50 52 Hoofed Animals Odd-toed Mammals Odd Mammals Whales Other Marine Mammals Seabirds Birds of Prey Songbirds Waterfowl Flightless Birds Penguins Fish Friends and Enemies at Sea Sharks and Rays Life of a Fish Reptiles Lizards Turtles Snakes Venomous Snakes Constrictors Crocodilians Amphibians Insects Insect Life Origin of Life Dinosaurs Armoured Dinosaurs Plant-eating Dinosaurs Meat-eating Dinosaurs Other Prehistoric Animals Plant Life Food for Plants Trees and Shrubs Aquatic Plants Climbers and Creepers Human Body External Body Parts Bones and Muscles Digestion and Excretion The Heart and Circulation The Brain and the Senses Reproduction and Birth Falling Sick 53 54 55 56 58 60 61 62 63 64 65 66 67 68 70 72 73 74 75 76 78 80 82 84 86 88 90 91 92 93 94 96 98 99 100 101 102-109 102 103 104 106 107 108 109 GrBigBk_Q_A 004-005 Content.qxd 21/5/07 12:10 pm Page 5 Continents, Countries and People 110-123 North America South America Australia and Oceania Europe Africa Asia The Poles – The Arctic and Antarctica World History Ancient Mesopotamia Ancient Egypt Ancient India and China Ancient Greece Ancient Rome Ancient Americas Native Americans Medieval Europe Medieval China and Japan Mughal India Incas and Aztecs The Renaissance Discovery of New Lands The British Empire The Industrial Revolution Scientific Revolution The American Revolution & Civil War The French Revolution Napoleonic Wars The World Wars The World after World War II Computer Revolution The New Millennium – 21st Century Art and Culture Architecture Art and Artists Music Theatre World of Sports World of Movies World Religions Science and Technology Matter Light Sound Heat Electricity Magnets 110 112 114 116 118 120 122 124-163 124 125 126 128 130 132 133 136 138 140 141 142 144 146 148 150 152 154 156 158 160 162 163 164-177 164 166 168 170 172 174 176 178-199 178 180 182 184 186 188 Forces and Motion Communication and Satellites Land Transport Water Transport Air Transport 190 192 194 196 198 World Map 200-201 Index 202-208 GrBigBk_Q_A 006-025.qxd 21/5/07 12:13 pm Page 6 Universe Galaxies The universe is a huge open space made up of billions of galaxies and an even larger number of stars. Our galaxy is called the Milky Way. Our solar system, including the Sun, the planets and their moons, forms just a tiny part of the Milky Way. Quick Q's: 1. What is the Big Bang theory? The Big Bang theory suggests that the universe as we know it today was created after a huge explosion or 'bang'. Georges Lemaitre proposed the theory of the Big Bang in 1927, and in 1929 Edwin Hubble expanded on his work. 2. Which is the largest galaxy? Scientists do not know exactly. The largest galaxies we know of are giant elliptical (oval) galaxies located in the middle of a whole group of galaxies. One of the largest is in the central galaxy in the cluster Abell 2029. 3. How big is the Milky Way? The Milky Way is huge. It takes the Sun about 250 million years to orbit once around the centre of the Milky Way. 4. What is Messier Object 31? The Andromeda Galaxy is also known as Messier Object 31, or M31. This galaxy is more than twice the size of Milky Way. But it is still not the largest galaxy we know of. 6 Q How was the universe formed? A The universe was born more than 15 billion years ago. It is believed that the universe began as a small ball of fire. This fireball grew larger and larger until one day it exploded, to form the universe that we know. Early universe Scientists think that the early universe was a dense cluster of matter, that has kept expanding from the Big Bang until now and is continuing to expand. Q How big is the universe? A No one knows how big the universe Q What is a galaxy? A A galaxy is a group of billions of stars, really is. There are at least 100 billion galaxies that we know of. However, this number keeps growing as better telescopes are developed and we see more and more galaxies. On top of that, the galaxies are moving away from each other, causing the universe to expand. Some scientists believe that the universe will never stop expanding, while others think that one day it will begin to shrink until it becomes a fireball again. dust and gas bound together by gravitational force. A galaxy can either be on its own or in a cluster. Galaxies come in different shapes and sizes. Scientists have divided them into three categories based on their shapes – spiral, elliptical (oval) and irregular (no shape). Expanding universe Scientists think that stars and other elements in the universe are continuing to move away from each other due to the force of the original Big Bang. GrBigBk_Q_A 006-025.qxd 21/5/07 12:13 pm Page 7 Galaxies Q How did the Milky Way get its name? A In ancient Greek and Roman myths, it was believed that the goddess Hera (Juno) spilt milk across the sky and called the white streak it left a 'river of milk'. The Romans called it Via Lactea or a 'road made of milk'. This is how our galaxy came to be named the Milky Way. A galactic crash Sometimes, galaxies crash into one another due to the force of gravity. But the stars in them are too far apart to cause any real damage. Our own galaxy is on a collision course with its neighbour Andromeda. The collision will take place in about five billion years and the two will merge to form an elliptical (oval) galaxy. Q Is the Milky Way a part of a cluster of galaxies? A The Milky Way and three of its neighbouring galaxies are part of a larger cluster known as the Local Group (because they are closest to Earth). The neighbouring galaxies in the Local Group are called Andromeda, and the Large and Small Magellanic Clouds. Of the 35 galaxies in the Local Group, only these three can be seen with the naked eye. Milky Way An artist's impression of our galaxy, the Milky Way, based on observations made by modern telescopes. Our Sun is a small star on one arm of the galaxy. Try these too… Stars (8–9), The Sun (10–11), The Planets (12–13), Comets and Asteroids (22–23), Scientific Revolution (150–151) 7 GrBigBk_Q_A 006-025.qxd 21/5/07 12:13 pm Page 8 Universe Stars A star is a huge ball of gas and dust that gives out both heat and light. When the gases in the star burn out, it dies. A star can live for millions, even billions, of years depending on its size. Each galaxy in the universe is made up of several billion stars. Quick Q's: 1. How many stars are there in the universe? We know of about 70 sextillion (7 followed by 22 zeros) stars in the universe. However, we are only able to see about 8,000 of these. 2. What are giant and dwarf stars? Scientists classify stars as giant or dwarf stars on the basis of their size. The Sun is a dwarf star. Supergiant stars – the biggest in the universe – are at least 400 times bigger than the Sun. 3. What is a cluster of stars? Stars are usually found in groups called clusters. Some clusters are made up of loosely packed stars, while other stars are packed tightly together to form a dense cluster. 4. What kind of stars are binary stars? Pairs of stars are called binary stars. Binary stars revolve around the same centre of gravity. 5. Which is the brightest known star? The Pistol Star is the brightest known star in the universe. It is about 10 million times brighter than the Sun. 8 Q What is a protostar? A Stars are born in clouds of dust and gases, mainly hydrogen. More and more gas is pulled together by gravity to form a cloud. After a while the cloud begins to spin. This makes the gas atoms bump into each other at high speeds, creating a great deal of heat. As the cloud becomes hotter a nuclear reaction takes place inside, and the cloud begins to glow. This glowing cloud is called a protostar. The protostar continues to contract until it becomes a star. Q How long does a star live? A A star glows for millions of years until the gases in its outer layer begin to cool, and the hydrogen in the inner core is slowly used up. The cool outer layer starts to glow red. When this happens the star is called a red giant. The red giant continues to lose its brightness until it fades away. Depending on its size, a red giant may die in an explosion, get compressed to form a black hole or become a white dwarf. Q What is a white dwarf? A A small star usually shrinks to form a dense white dwarf. The size of a white dwarf is similar to the size of Earth. There are many white dwarfs in our galaxy but they are too dim to be seen. Sirius B is one of them. White dwarf An enhanced image of white dwarf stars, which have already shrunk to a size comparable to that of the Earth. These stars are too dim to be detected without modern telescopes. Protostar An artist's impression of the original ball of dust and gases that combine to form a protostar. Q What is a supernova? A A supernova is a vast explosion in which an entire star is destroyed. After the explosion, extremely bright light is emitted for several days. Supernovas appear a billion times brighter than the Sun. Sometimes, a supernova explosion can go on for weeks or even months. Supernovas mostly occur in distant galaxies. The last supernova to take place in the Milky Way occurred in 1604. It was observed by the famous astronomer Johannes Kepler. The brightest supernova to be recorded so far is 1993J in the galaxy M81. It was seen on 26 March 1993. But because the stars are so far away, we may see a supernova explosion long after it takes place. GrBigBk_Q_A 006-025.qxd 21/5/07 12:13 pm Page 9 Stars Q What is a black hole? A Black holes are extremely compact space objects that were once massive stars. Sometimes a huge star begins to shrink until it is smaller than an atom. This is called a black hole. The centre of the black hole is called 'singularity'. The gravity near this point is so strong that any object that gets too close to the black hole is pulled into it. Even light gets sucked into it, which is why we can't see a black hole. Scientists use special instruments to detect a black hole's presence. They examine the effects it has on the objects near it. Dwarf stars When stars reach the end of their lives, their fires start to die out, and then they become dwarf stars due to the gravitational pull of the matter inside. Black hole Nobody can actually see a black hole, because the extremely strong gravity inside them does not even allow any light to escape, let alone anything else. This is an artist's impression of what a black hole may be like. Heavenly pictures Try these too… By drawing imaginary lines between the stars in the sky, you will notice the shapes of animals or objects familiar to you. You might see a crab, a dragon, a bear or other patterns. These star patterns are called constellations. Astronomers have identified 88 constellations in all. The more famous ones are the Great Bear, the Little Bear and Orion, also known as the Hunter. The constellations also include characters from Greek mythology and the 12 signs of the zodiac. Galaxies (6–7), The Sun (10–11), The Planets (12–13), The Moon (20–21), Humans in Space (24–25), Earth's Atmosphere (26–27), Scientific Revolution (150–151), Computer Revolution (162), Matter (178–179), Light (180–181), Heat (184–185), Electricity (186–187), Forces and Motion (190–191), Communication and Satellites (192–193) 9 GrBigBk_Q_A 006-025.qxd 21/5/07 12:13 pm Page 10 Universe The Sun Our solar system is made up of the Sun, eight planets, three dwarf planets and many asteroids, comets and other space rocks. The Sun is the largest object in the solar system and is located right at its centre. The planets, dwarf planets, asteroids and comets travel around the Sun in an ellipse. Our solar system was formed about 5 billion years ago, and the surface of the Sun is about 4.6 billion years old. Quick Q's: 1. What are sunspots? Sunspots are storms on the surface of the Sun. These storms appear as huge, dark spots in satellite pictures and so are called sunspots. 2. How hot is the Sun? The Sun's surface temperature is about 5,760 °C (10,400 °F), while its centre is an incredible 15 million °C (28 million °F) – that is more than 150,000 times hotter than boiling water! 3. How far is the Sun from us? The Sun is about 150 million kilometres (93 million miles) away from the Earth. 4. What is the corona? The corona is the glowing atmosphere of the Sun that extends millions of kilometres into space. The corona is 200 times hotter than the Sun's surface! 5. Is the sun worshipped by people? The sun has been worshipped as a god since ancient times by the Greeks, Romans and native Americans. 10 Q How was the Sun created? A Before it was formed, the Sun and the rest of the solar system was a huge mass of hot gas and dust called a solar nebula. This nebula spun faster and faster until the clouds of gases, dust and ice particles clumped together and exploded, forming the sun. Q Why does the Sun glow? A The Sun is made up of huge amounts of hydrogen and helium gases. Nuclear reactions at the centre of the Sun emit a large amount of energy that makes the Sun glow. That same energy travels through space and reaches us as heat and light. Q What is a solar eclipse? A A solar eclipse occurs when the Moon comes between the Sun and the Earth, blocking the Sun from our view. In a total solar eclipse, the Moon blocks out the Sun from our view completely. In a partial eclipse, however, a part of the Sun is visible. During an annular eclipse, we can see a small ring of the Sun glowing around the Moon. When the Moon is nearer to the Earth it appears larger and therefore covers the Sun completely, although it is actually much smaller than the Sun. However, in an annular eclipse the Moon is too far away from the Earth to block the Sun out totally and therefore a ring of sunlight is seen. Flaring up! Solar flares on the surface of the Sun. Solar flares were observed for the first time in 1859. Q What is a solar flare? A Sometimes the Sun produces a huge amount of magnetic energy that sends out jets of gas into space. These jets of gas are called solar flares and cause a sudden increase in the brightness of the Sun. Solar flares are often followed by the release of electrically charged particles like protons and electrons. These are called solar winds and are known to travel at a speed of about 500 kilometres (300 miles) per second. Blocking the Sun In an annular (ring-shaped) eclipse, the Moon covers only the middle portion of the Sun, causing a bright ring of light to appear around the Moon. GrBigBk_Q_A 006-025.qxd 21/5/07 12:13 pm Page 11 The Sun Q Is the Sun really a star? A The Sun is a medium-sized star known as a yellow dwarf. It is younger and smaller than most stars in the universe, but is very bright and extremely hot. In about five billion years, when all the hydrogen in its core has been used up, the Sun will change into a red giant star. After that, the Sun will evolve into a white dwarf before finally dying out. A joint effort The SOHO was launched jointly by the European Space Agency and NASA. For over ten years, SOHO has been studying the outer layers of the Sun. Q How did we learn about the Sun? A We have sent several solar missions into space to study the Sun and its characteristics. The first detailed observations were made by NASA's Pioneer missions that were launched between 1959 and 1968. The Solar Maximum mission of 1980 made a detailed study of solar flares. The Solar and Heliospheric Observatory (SOHO) launched in 1995, has been continuously collecting data regarding the Sun for the last ten years. In different directions! The Sun takes about 26 days on average to rotate on its axis. Since it is made up of gas, different parts of the Sun rotate at different speeds. The surface closest to the equator rotates faster than that closest to the polar regions. The Sun's surface near the poles takes almost 36 days to complete one rotation. N Try these too… S Surface of the Sun There is constant activity visible on the surface of the Sun, as it pulses and glows due to the heat and light produced by the nuclear reactions within. Galaxies (6–7), The Planets (12–13), The Moon (20–21), Earth's Atmosphere (26–27), Scientific Revolution (150–151) 11 GrBigBk_Q_A 006-025.qxd 21/5/07 12:13 pm Page 12 Universe The Planets Planets are large masses of matter that orbit around a star. Our solar system consists of eight planets – Mercury, Venus, Earth, Mars, which are called inner or rocky planets, and Jupiter, Saturn, Uranus and Neptune, which are the outer planets, or gas giants. Quick Q's: 1. How did the planets get their names? All the planets are named after Roman gods. Venus is named after the Roman goddess of love. The surface features of Venus are also named after various goddesses. For example the planet has a deep canyon named Diana, after the Roman goddess of hunting. 2. How many rings do Jupiter and Uranus have? Jupiter has three thin rings that cannot be seen even with the most powerful telescopes. Uranus has as many as 11 rings. 3. How many moons does Venus have? Apart from Mercury, Venus is the only other planet in the solar system that has no moon. Q How were the planets formed? A After the gaseous cloud called the solar nebula collapsed upon itself due to the strength of its own gravity and formed the Sun, the dust and particles around it clumped together to form the planets. The heat of the Sun melted the ice particles nearby and eventually these rocks grew larger to form the four rocky planets. Some ice particles were too far away from the Sun to be melted. These ice pieces combined with gases to form the planets called the gas giants. Birth of planets The planets in our solar system were born when dust and particles around the Sun clumped together. Earth Uranus Jupiter Neptune Saturn Gas giants The four outer planets, the gas giants, are much larger than the Earth. Q What are the features of a rocky planet? Q What makes gas giants unique? A The rocky planets are made up of rocks A The gas giants are bigger in size but and metals like iron and nickel. They are smaller than the gas giants but are very heavy. It is because of their weight that rocky planets rotate much slower than the gas giants. Rocky planets Among the rocky planets, the Earth appears blue from outer space because over 70 per cent of its surface is covered with water. lighter, as they are mainly made up of gases and ice particles. In fact, Saturn is so light that it would float if placed in water! Gas giants also spin extremely quickly and they have rings around them. These planets do not have a hard surface. Jupiter and Saturn have a semi-liquid centre that is covered by a layer of liquid gas. 4. What about Pluto? Until recently, Pluto was the ninth planet in our solar system. But in 2006, it was officially reclassified as a dwarf planet, because it is so small and its gravitational field is not as strong as that of the major planets. 12 Mercury Mars Venus Earth GrBigBk_Q_A 006-025.qxd 21/5/07 12:13 pm Page 13 The Planets Try these too… Q What are the distinguishing features Galaxies (6–7), The Sun (10–11), The Hot Planet (14), The Earth's Twin (15), The Red Planet (16), The King of Planets (17), The Last Planets (18), Dwarf Planets (19), The Moon (20–21), Earth's Atmosphere (26–27) 1 of each of the rocky planets? 2 A Mercury is the closest to the Sun and JUPITER therefore its temperature can be as high as 467 °C (873 °F). Venus is covered with carbon dioxide containing droplets of sulphuric acid. This traps the Sun's heat and makes Venus hotter than even Mercury. Mars, the red planet, is considered to be the only planet after Earth where life could exist. As far as we know, the Earth is the only planet that supports life. Q What are the special characteristics of the gas giants? A Jupiter is the largest planet. It rotates faster than any other planet and has the most moons. Saturn is set apart by its beautiful rings, made up of dust particles and pieces of ice. Uranus is a strange planet where seasons last for more than 20 years, while Neptune is the windiest planet in the solar system. 3 1 2 3 4 Amalthea Adrastea Metis Thebe 4 Jupiter's moons Jupiter, the largest planet in the solar system, has so many moons that we are constantly discovering new ones. This image shows some of the bigger moons and the gossamer rings around the planet. Saturn's moons At least 46 moons orbit Saturn. Each moon is unique. Enceladus is among the shiniest objects in space. Titan's atmosphere is thicker than Earth's. Here are the big moons, seen from behind the moon Dione. The solar system The relative sizes of the eight planets and the three dwarf planets are shown in this diagram of the solar system. Jupiter is the largest planet. The Sun, of course, is much larger than any of the planets. Titan Enceladus Rhea Saturn Mimas Tethys Dione PLANETS 1 3 4 5 6 7 1 2 3 4 5 6 7 8 8 2 Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune DWARF PLANETS 9 Ceres 10 Pluto 11 2003 UB 313 9 10 11 13 GrBigBk_Q_A 006-025.qxd 21/5/07 12:13 pm Page 14 Universe The Hot Planet Mercury is the planet closest to the Sun. It is also very small – about the size of Earth's moon. It is named after the Roman messenger god because it moves very quickly. Quick Q's: Q Why are nights on Mercury freezing cold, 1. How long does Mercury take to orbit the Sun? although it's the planet closest to the Sun? Like all planets, Mercury goes around the Sun in an elliptical (oval) orbit. It takes about 88 days to complete one orbit. 2. How long is a day on Mercury? Mercury goes around the Sun very fast, but rotates very slowly on its axis. Therefore a day on Mercury is equal to 176 Earth days! 3. Why does Mercury have huge craters? As Mercury has very little atmosphere, meteors do not burn up in the air. Instead, they fall on the surface, creating huge craters. 4. What colour is the sky above Mercury? A Unlike Earth, Mercury is not surrounded by a thick protective blanket of air called the atmosphere. This means that the heat from the Sun escapes, leaving the planet freezing at night. While the temperature during the day can be as high as 467 °C (873 °F), at night it drops to -183 °C (-297 °F). Q What is the surface of Mercury like? A If you were to land on mercury, you would find a surface very similar to that of the Moon. It has dust-covered hills, cliffs and is dotted by craters. The planet also has a thick metallic core and a sandy crust. solar panel Sun shade Sandy surface Mercury has a surface that is full of hills and steep canyons, all of it covered with a mixture of sandy substances. The core of the planet is metallic, like all the rocky planets. Q What space probes have been launched to Mercury? A Mercury, being so close to the Sun, is very difficult to explore. Space probes are unable to withstand the heat of the planet. Only one space probe, Mariner 10, has visited Mercury so far. It photographed nearly half of the planet's surface. A new probe, Messenger, is on its way to Mercury. It was launched on 3 August 2004 and is expected to return, after photographing the whole planet, in March 2012. Another space mission will begin in 2013. TV cameras If you were to look at the sky from Mercury, even during the day, it would appear black. This is because there is no atmosphere to spread the Sun's light. 5. Which is the largest crater on Mercury? The largest crater is the Caloris Basin. It is about 1,300 kilometres (808 miles) in diameter. It is also one of the biggest craters in the solar system. 14 Mercury close-up From up close, the surface of Mercury can be seen to be pitted with huge craters. Any meteor that comes near Mercury falls on the surface and creates a crater, as there is no atmosphere to burn the meteor up. Looking at Mercury The Mariner 10 space probe is the only one to have got anywhere near Mercury so far. It is sending photographs of the surface of Mercury regularly now. GrBigBk_Q_A 006-025.qxd 21/5/07 12:13 pm Page 15 The Earth's Twin The Earth's Twin Venus is the second planet from the Sun. It is also Earth's closest neighbour and its size, composition, gravity and distance from the Sun are similar to the Earth's. Venus is so similar to Earth, that it is often considered to be its twin. However, in reality, Venus is very different. Q Why is Venus hotter than Mercury? A Venus has a thick atmosphere, much thicker than the Earth's. The atmosphere is mainly carbon dioxide. This greenhouse gas traps large amounts of heat within the planet. That is why Venus is hotter than Mercury, though Mercury is closer to the Sun. Q Why is a day longer than a year on Venus? A Venus goes around the Sun at a very high speed. It takes only about 225 days to complete one orbit. However, it spins much more slowly on its axis, taking about 243 days to complete a rotation. Therefore, days on Venus are longer than years. Mapping Venus Scientists have sent a number of space missions to Venus to find out more about its size, atmosphere, interior and surface, especially its volcanoes. Q Are there volcanoes on Venus? A There are more volcanoes on Venus than there are on Earth. About 80 per cent of the planet's surface is made up of smooth volcanic plains, and there are two major mountain ranges with volcanoes that may be active. The peak of Maxwell Montes, the highest mountain on Venus, lies 11 kilometres (7 miles) above the surface of the planet. Mount Everest rises only about 9 kilometres (6 miles) above sea level. Try these too… The Sun (10–11), The King of Planets (17), The Moon (20–21), Comets and Asteroids (22–23), Earth's Atmosphere (26–27), The Poles – The Arctic and Antarctica (122–123) Volcano on Venus There is far more volcanic activity inside Venus than inside Earth; so, Venus has many more volcanoes. Spinning backwards All the planets rotate from west to east on their axes, apart from Venus, which spins in the opposite direction. On the surface of Venus, the Sun appears to rise in the west and set in the east. The planet might have been hit by a huge space rock, reversing the direction of its spin. Earth rotation Sun Venus 15 GrBigBk_Q_A 006-025.qxd 21/5/07 12:13 pm Page 16 Universe The Red Planet Mars is the fourth planet from the Sun and is named after the Greek god of war. It is also called the red planet because it glows red in the sky. The presence of rust (iron oxide) on its surface gives the planet its colour. Quick Q's: Q What is the 1. Can you see Mars from the Earth? surface of Mars like? On a clear night, Mars can be observed with the naked eye. Between July and September the Martian surface can be observed clearly through a telescope. 2. How many moons does Mars have? Mars has two moons called Phobos and Deimos, which orbit very closely to its surface. Both moons are believed to be asteroids that were captured by the gravity of Mars as they came close to it. 3. Is there life on Mars? The atmosphere of Mars is 95 per cent carbon dioxide, 3 per cent nitrogen and 1.6 per cent argon. Traces of oxygen and water have also been found. Some scientists have claimed to have found traces of methane. This gave rise to the speculation that there may be life on Mars, since methane is a gas produced by many animals. But other scientists pointed out that methane is also produced by the mineral olivine, which can be found on Mars. 16 Martian moon The two moons of Mars are quite small compared to our Moon. They may be asteroids caught by the gravity of Mars. Red planet The surface of Mars looks reddish brown due to the presence of iron oxide. The scientists have also found signs of frozen water near the South Pole of Mars. It is believed that huge floods flowed through Mars about 3.5 billion years ago. The water from the floods may have once collected in huge basins. A The surface of Mars is divided into the northern plains flattened by lava flows, and the southern highlands marked by huge craters. The planet boasts Olympus Mons, the largest volcano in the solar system. Q Is there water on Mars? A Scientists have found signs of water in rock layers. In 2006, the scientists saw new deposits of sediment on the surface of Mars. These sediments had not been there six years earlier. According to scientists at NASA, this is the strongest evidence so far that water still flows occasionally on the surface of Mars, though other scientists say the sediments could have been deposited by carbon dioxide frost or movement of dust. Samples of the minerals haematite and goethite have also been found in Mars. These minerals are sometimes formed in the presence of water. Olympus Mons The tallest volcano in the solar system, Olympus Mons towers 27 kilometres (16.88 miles) above the surface of Mars. Q Why are seasons on Mars longer than on Earth? A Mars and Earth are tilted on their axis in the same way. Therefore, Mars has almost the same kind of seasons as Earth. However, because a Martian year is equal to two years on Earth, each Martian season lasts twice as long as the seasons on Earth. Q What kind of weather would you find on Mars? A The temperature varies from -140 to 20 °C (-220 to 68 °F). The polar ice caps on Mars increase and decrease in size alternately in winter and summer. Mars also has dust storms, which can cover the entire planet. Look out for Mars From 27 August 2006, Earth and Mars have been closer to each other than they have been in the last 60,000 years! It has begun to appear brightly in the night sky, as seen here while looking south-east from Poodle Rock in the Valley of Fire State Park, Nevada, USA. Now Mars will be the brightest object in the night sky after the Moon and Venus. GrBigBk_Q_A 006-025.qxd 21/5/07 12:13 pm Page 17 The King of Planets The King of Planets Jupiter is the first of the gas giants and the fifth planet from the Sun. It is the largest of all planets. In fact, more than a thousand Earths could fit inside it! Q How did Jupiter get its name? A The planet is named after the king of the Roman gods. It is indeed the king of the planets, not just because of its massive size, but also because it rotates the fastest. It is the fourth brightest object in the sky, after the Sun, the Moon and Venus. Q How many moons does Jupiter have? A Jupiter has more than 60 moons. Galileo Galilei, the famous Italian astronomer, saw the four largest moons of Jupiter in 1610. They were named Io, Europa, Callisto and Ganymede. By the 1970s nine more moons were discovered and today we know of 63. Volcanic moon Io, one of the four largest moons, lies very close to Jupiter. There is a great deal of pressure on this small moon, since it is constantly being pulled by the gravity of Jupiter and the other large moons. This tug of war generates a lot of heat, so Io is covered with active volcanoes. Q What is the Great Red Spot? Great Red Spot A Jupiter is a planet of storms. The biggest storm area is called the Great Red Spot. It has been raging for at least 340 years. It is so big that it can be seen from the Earth through a telescope. Q How many explorations have been made to Jupiter? A Many explorations have been made to the king of planets. Pioneer 11 took the first close-up images in 1974, studied the atmosphere and detected Jupiter's magnetic field. Space probe Galileo, launched in 1989, orbited Jupiter. In 2000, the Cassini probe took the best ever photos. Planet spotter The Galileo space probe was the first to make an entire orbit around Jupiter. Giant ball of gas There are constant storms on Jupiter, during which the winds can roar five times faster than the fastest hurricane on Earth. Some of the big storms are seen here in brown. Try these too… The Sun (10–11), The Planets (12–13), The Last Planets (18), The Moon (20–21), Comets and Asteroids (22–23), Scientific Revolution (150–151), Communication and Satellites (192–193) 17 GrBigBk_Q_A 006-025.qxd 21/5/07 12:13 pm Page 18 Universe The Last Planets Next to Jupiter are Saturn, Uranus and finally Neptune. Saturn is the second largest planet in the solar system. Like Jupiter, Saturn and Uranus are made up of gases. All three planets have rings, but it is Saturn's rings that are the most spectacular. Q Why do Saturn's rings shine? A Saturn's rings consist of dust particles and pieces of ice that can be quite large. The ice pieces reflect light, causing the rings to shine. Saturn's rings Saturn has seven large rings, each made up of thousands of smaller rings. These are among the brightest objects you can see through a telescope. Quick Q's: 1. How big are Saturn's rings? Q What gives Uranus and Neptune their blue colour? A Both planets contain methane. Sunlight is reflected by clouds under the methane layer. Only the blue portion of the reflected light passes through the methane layer, so they appear to be blue. Strange rotation Uranus rotates from top to bottom as it orbits the Sun. Saturn's rings can be up to 1 kilometre (0.6 miles) thick and stretch for over 280,000 kilometres (175,000 miles). 2. When were Saturn's rings discovered? 4 Uranus was the first planet to be seen through a telescope. It was discovered in 1781 by astronomer William Herschel. 18 URANUS 3 1 1 2 3 4 5 over 20 years? A Uranus has a very peculiar orbit, unique in the solar system. The planet is tilted in such a way that its poles face the Sun directly, so that Uranus spins from top to bottom. It acts like a cylinder that is rotating on its ends instead of rotating on its sides. Scientists believe that another planet-like object might have crashed into Uranus, knocking it over on to its side. The long seasons are caused by the planet's unusual orbit. Q Are there winds on Neptune? A Neptune is the windiest planet in our Cloudy over Neptune The clouds over Neptune are always being blown about by the strong winds on the planet. 2 3. Who discovered Uranus? Q Why do seasons on Uranus last for solar system. Winds on this planet can reach speeds of about 2,000 kilometres per hour (1,200 miles per hour). That is more than ten times the speed of the strongest hurricane on Earth. 5 Saturn's rings were first observed by Galileo through a telescope in 1610. Probing far The Cassini space probe is expected to send us better photographs of the far planets. Pole Equator Juliet Bianca Puck GrBigBk_Q_A 006-025.qxd 21/5/07 12:13 pm Page 19 Dwarf Planets Dwarf Planets In 2006, the International Astronomical Union (IAU) made a decision that changed the way we organize our solar system. The IAU announced the removal of Pluto from the list of planets. They reclassified Pluto as a dwarf planet. Instead of nine, we now have only eight planets in our solar system. Q How is a dwarf planet different from Q How many dwarf other planets? planets are there in the solar system? A According to the IAU's new definition, A Apart from a planet is a space object that orbits the Sun and has a nearly round shape. Its gravity must be strong enough to clear all other space objects (except satellites) out of its orbit. Dwarf planets also orbit the Sun and have a nearly round shape. But other space objects nearby are not cleared by the gravity of the dwarf planets. They are not big enough for their gravitational fields to do this. Dwarf planets are different from satellites, which orbit a planet and not the Sun. Pluto, Ceres and Eris (UB313) have also been classified as dwarf planets. Until recently, Ceres was called the largest asteroid. It has a diameter of about 950 kilometres (600 miles) and is in the asteroid belt between Mars and Jupiter. Eris is the largest of all the dwarf planets. It has a diameter of about 3,000 kilometres (1,850 miles). Q Are there any other dwarf planets? A Scientists are considering including Distant Sun An artist's impression of how the Sun would look from the surface of Eris, the furthest of the dwarf planets in the solar system. The Sun gives almost no heat at that distance and looks like a bright star. Pluto's moon Charon among the dwarf planets. Charon does not actually go around Pluto – they revolve around each other. The planetoid Sedna and the asteroids Vesta, Pallas and Hygiea are also being considered. 1 2 3 4 5 Sun Mercury Venus Earth Mars 6 7 8 9 10 Jupiter Saturn Uranus Neptune Pluto Try these too… The Sun (10–11), The Planets (12–13), The Red Planet (16), The King of Planets (17), The Last Planets (18), The Moon (20–21), Comets and Asteroids (22–23), Scientific Revolution (150–151), The New Millennium – 21st Century (163) Pluto's moon Pluto (left) and its moon Charon actually go around each other, rather than Charon going around Pluto. Scientists may soon reclassify Charon as dwarf planet. Thrown off orbit Pluto was called the ninth planet for 76 years. After 2006, it was reclassified as a dwarf planet. Promoted Since 2006, Ceres is classified as a dwarf planet. Before that, it was simply the largest of the many asteroids that lie between the orbits of Mars and Jupiter. 10 6 5 9 8 2 1 4 7 3 19 GrBigBk_Q_A 006-025.qxd 21/5/07 12:13 pm Page 20 Universe The Moon There are many moons in our solar system, which orbit planets, just like planets orbit the Sun. Earth has one Moon, Mars has two small moons, Mercury and Venus don't have any, while Jupiter has at least 63! The Earth's Moon is made up of rocks, both solid and molten. Quick Q's: 1. Does our Moon have a scientific name? Astronomers call the Earth's Moon Luna, to distinguish it from the natural satellites of other planets. 2. If the Moon is cold and dark, how does it give off light? The Moon does not give off light of its own. It simply reflects the sunlight that falls on it. 3. Why can't we see the Moon during the day? During the day the bright light of the Sun blocks the soft glow of light reflected by the Moon. 4. What are spring tides and neap tides? When the Sun, the Moon and the Earth are in a straight line, the gravitational force of the Sun strengthens that of the Moon causing tides that are higher than usual. These are called spring tides (although they have nothing to do with the season of Spring). When the Sun and the Moon are at right angles to the Earth, weaker tides, called neap tides, are caused. Tides are important to wash away the debris off the coasts. 20 Q Why is the Moon's surface filled with craters? A The Moon does not have an atmosphere. Therefore, meteors and asteroids from outer space crash into its surface making craters. Tycho crater, one of the biggest lunar craters, is more than 85 kilometres (50 miles) wide. Q What does the term 'Blue Moon' mean? Blue Moon refers to the second Full Moon to appear in a month. It is very rare indeed. There are other definitions of Blue Moon as well, but this is the most widely accepted definition nowadays. Q How does the Moon cause tides in our oceans and seas? A Tides are caused by the gravitational force exerted by the Moon on our planet. This force causes the ocean to bulge out in the direction of the Moon, making the tide rise. As the Earth is also pulled towards the Moon, the ocean on the side facing away from the Moon also bulges out. So it is high tide there as well. In the region between the two bulges (high tides) the water level decreases, causing low tides. Tides are higher in the tropics due to the bulge of the equator. Many forms of life on the coast are tailored to the cycle of tides. High and low The gravitational pull of the Moon on the Earth causes tides in the oceans and seas of the Earth. Crescent Moon As the Moon orbits around the Earth, we see only a part of it that is lit up by the Sun, depending upon the angle made by the Earth, the Moon and the Sun. Q Why does the Moon appear crescentshaped at times? A The shape of the Moon as seen from the Earth keeps changing. The changing shapes of the Moon are called phases. When the side of the Moon that faces the Earth is turned away from the Sun, we are unable to see the Moon. This phase is called the New Moon. As the Moon travels in its orbit around the Earth, we start to see a small portion of the Moon that is lit up by the Sun. This is called the Crescent Moon. The lit up portion seen by us slowly increases, and we see a Half Moon, then a Three-quarter Moon. When the Moon completes a half orbit around the Earth, we can see the entire disc lit up by the Sun – the Full Moon. Neap Tide Spring Tide Sun Low Tide High Tide High Tide Low Tide Neap Tide Spring Tide GrBigBk_Q_A 006-025.qxd 21/5/07 12:13 pm Page 21 The Moon The dark side Did you know that we see only one side of the Moon at all times? This is because the Moon takes the same amount of time to rotate on its axis as it takes to go around the Earth. The side we see is called the near side, while the one that is never seen is called the dark side. The first time people on Earth got to see the dark side of the Moon was when the first astronauts made an orbit around the Moon, and took photographs. The astronauts lost touch with Earth when they were on the dark side, because the moon blocked their radio signals. Phases of the Moon We see different parts of the Moon lit up by the Sun, depending upon how much of the Moon that is lit up is facing towards us or facing away from us. This is repeated in a cycle every 28 days. Try these too… The Sun (10–11), The Planets (12–13), Humans in Space (24–25), Oceans (34–35), Forces and Motion (190–191) 21 GrBigBk_Q_A 006-025.qxd 21/5/07 12:13 pm Page 22 Universe Comets and Asteroids Along with the Sun, the planets and their moons, several other objects made up of small pieces of rock, metal and ice are also a part of the solar system. These objects are asteroids, comets and meteors. Mars Mercury Quick Q's: 1. What are sungrazers? Some comets crash into the Sun or get so close to it that they break up into tiny pieces. Such comets are called sungrazers. 2. Where are asteroids found in the solar system? Most asteroids are found in a region between Mars and Jupiter, which is known as the asteroid belt. 3. Do asteroids have moons? The asteroid Ida has a tiny moon, Dactyl. This was discovered by the spacecraft Galileo in 1993. 4. When will Halley's Comet be seen again? Halley's Comet takes about 76 years to complete one orbit around the Sun, so it is expected to be seen again in 2061. 5. Why does a comet have a tail? A comet is made up of ice and other material. As it nears the Sun, these materials heat up. Solar wind and pressure from the Sun's radiation push them outwards to form a tail that always points away from the Sun. 22 Q Are asteroids planets? A When the solar system was formed, some fragments of rock were left spinning in space. These huge space rocks that orbit the Sun are called asteroids. Like other planets, asteroids are also made of metals like iron and have moons. Some of them are called minor planets. Q Are asteroids dangerous? A An asteroid can be thrown off its orbit by the gravity of larger planets, or if it comes too close to another asteroid. Once it is off its orbit, the stray asteroid often strikes the surface of other planets and moons. This causes widespread destruction and creates huge craters. In fact, some scientists think that an asteroid struck Earth about 65 million years ago, causing the extinction of the dinosaurs. Q Are shooting stars really stars? A Shooting stars are actually pieces of burning rock called meteors. A meteor is formed when a piece of debris in the solar system, called a meteoroid, enters the Earth's atmosphere. As the meteor rubs against the air in the Earth's atmosphere, it gets hotter and hotter until it burns up in a streak of light. A meteor We can see a meteor without a telescope when it enters the Earth's atmosphere. Sometimes, a number of meteors are seen within a very short period of time. They leave a streak of light, which disappears very quickly. This is called a 'meteor shower', also known as 'meteor storm'. Venus Earth Jupiter Asteroid belt Most of the asteroids in our solar system can be found in a belt between the orbits of Mars and Jupiter. Q How is a comet's tail formed? A A comet is a mixture of ice, gas and dust. Like asteroids, they too travel around the Sun. As a comet nears the Sun, the ice on its surface melts and a jet of gas and dust particles is released to form a tail. Comet tails can be as long as 10 million kilometres (6.2 million miles). GrBigBk_Q_A 006-025.qxd 21/5/07 12:13 pm Page 23 Comets and Asteroids Q Do meteors ever fall on Earth? A Sometimes small fragments of a meteor, called meteorites, crash on to the surface of the Earth. Some are so big that they make craters where they fall. Many meteorites have been found on the Earth's surface. The best known of these is the Barringer Impact Crater in Arizona, USA. This crater was created by an iron meteor that fell on the Earth about 50,000 years ago. The meteor was almost 40 metres (130 feet) in diameter and slammed into the surface at a speed of about 11 kilometres per second (6.8 miles per second), creating a crater that was more than a kilometre wide. The great Siberian explosion On 30 July 1908 people living near Lake Baikal in Siberia saw a strange bluish light travel across the sky, followed by a loud explosion and shockwaves that knocked people off their feet. The explosion took place near the Stony Tunguska River and was probably caused by a meteor. It flattened about 80 million trees. The meteor may have broken up about 10 kilometres (6 miles) above the Earth's surface, so it did not leave a crater. Huge crater The Barringer impact crater in the USA was created by a meteorite impact 50,000 years ago. Q Where do comets come from? A Comets originate in two different areas of the solar system. Comets from the Kuiper Belt beyond Neptune are called short-period, since it takes them less time than other comets to go around the Sun. Comets from the Oort Cloud take as long as 30 million years to complete one orbit and are therefore called long-period comets. There are about a trillion comets in the Oort Cloud. The Oort Cloud itself is at the edge of the solar system, almost a quarter of the way from the Sun to the next star, Proxima Centauri. Regular visitor Halley's Comet orbits around the Sun once every 76 years, and is the most famous comet in human history. Try these too… The Sun (10–11), The Planets (12–13), Humans in Space (24–25), Earth's Atmosphere (26–27), Scientific Revolution (150–151), Forces and Motion (190–191) 23 GrBigBk_Q_A 006-025.qxd 21/5/07 12:13 pm Page 24 Universe Humans in Space Ever since ancient times, humans have wanted to know more about the skies above them. They invented stories to explain the presence of the stars, the Moon and the Sun. Today, advanced technology helps us to travel into space and expand our knowledge about the world beyond our planet. Q How do space shuttles fly into space? A A space shuttle consists of two rocket First woman in space Valentina Tereshkova was the first woman in space, aboard Vostok 6 on 16 June 1963. Quick Q's: 1. What was the first living being to orbit Earth? The first creature to orbit the Earth was a dog named Laika, aboard the Russian spacecraft Sputnik 2 on 3 November 1957. 2. Who was the first person in space? On 12 April 1961, Russian cosmonaut Yuri Gagarin was the first person to travel in space, aboard the spacecraft Vostok 1. Gagarin orbited the Earth once on this historic flight, which lasted 1 hour and 48 minutes. 3. Which was the first ever space station? Salyut 1 was the first space station. It was launched on 19 April 1971. 24 boosters, three engines, an external fuel tank and two smaller fuel tanks. It also has an orbiter, which puts the shuttle into orbit. The rockets are used to propel the shuttle into space. When the shuttle is about 45 kilometres (28 miles) high, the rockets fall off into the ocean and the three main engines of the shuttle take over. Just before the shuttle goes into orbit, its engines are shut down and the external fuel tank is discarded. Q Why can't I fly into space in an aeroplane? A All objects, even aeroplanes, are glued to the surface of the Earth by gravity. If you wanted to escape this unseen force, you would have to travel at a speed of at least 40,000 kilometres per hour (25,000 miles per hour). Only space shuttles are designed to achieve this speed. A mixture of liquid hydrogen fuel and liquid oxygen is burned under high pressure to help the shuttle's rockets reach this speed and push it out of the Earth's atmosphere into orbit. Weightless games On board a spacecraft, astronauts dance in zero gravity, as one colleague holds down a keyboard to play it. Q Is there no gravity in space? A All objects in space exert some gravitational force on each other. However, the gravitational force exerted by some objects, like the Moon, is much less than that of the Earth. When humans are in space they float around in the air, because there is not enough gravity to keep their feet on the ground. Take off These three images show the space shuttle at its base (left), at the moment of take off (centre) and on its way to space (right). GrBigBk_Q_A 006-025.qxd 21/5/07 12:13 pm Page 25 Humans in Space Q Could I see the Sun rise and set from space? A Astronauts aboard a space shuttle orbiting the Earth actually see 16 sunrises and sunsets every day! This is because once in orbit, a space shuttle goes around the Earth at a speed of more than 28,000 kilometres per hour (17,400 miles per hour) and takes only 90 minutes to complete one orbit. Q Is it possible to live in space? A Today astronauts spend a great deal of time in space stations. A space station is a floating space base. It is like a spaceship designed so that astronauts can live in outer space for weeks, months or even years at a time. Unlike a spacecraft, a space station cannot take off or land on planets. Other vehicles are used to transport people and materials to and from the station. Space stations are used for studying the effect of long-term space flights on the human body as well as for space research. Q Is sending humans into space the only way to learn more about it? A Apart from sending astronauts into space, we also use satellites, probes and telescopes to study space. Like moons, man-made satellites revolve around planets and help us learn more about them. A probe is an unmanned spacecraft sent into space to study objects other than the Earth. We have even put huge telescopes into orbit. The Hubble Space Telescope, sent into orbit in 1990, is the best-known among these. It is better to have a telescope in space than on Earth, because then there is no atmosphere to distort the image received by the telescope. However, the biggest telescopes are too big to be sent to space. Many sunrises and sunsets When astronauts are on board a spacecraft and orbiting the Earth, they are moving much faster than the Earth, so they can see the Sun rise and set many times in a day. The normal human biological cycle can be upset by this, so astronauts are given special medicines to help them sleep. Try these too… The Planets (12–13), The Red Planet (16), The Moon (20–21) Looking back in time The Hubble Space Telescope works like a time machine that can travel into the past. It took pictures of the universe when it was barely a billion years old – the universe is at least five billion years old now, though some scientists put its age as high as 14 billion years. The Hubble Space Telescope can look into the past because it takes billions of years for light from the far ends of the universe to reach the telescope. When the light reaches it an image is captured, and we can see what happened in that particular part of the universe long ago. 25 GrBigBk_Q_A 026-041.qxd 21/5/07 12:15 pm Page 26 Planet Earth Earth's Atmosphere The protective blanket of air that covers the Earth is called the atmosphere. The Earth's atmosphere not only prevents too much heat from entering the planet, but also protects us from asteroids and meteors. The Earth's gravity helps hold the atmosphere in place. 1. What is a barometer? A barometer is used to measure the pressure in the atmosphere. When the pressure is high, the weather will be fine, sunny and still. When it is low, the weather will be stormy. When the pressure increases the liquid in the barometer is squeezed and when the pressure decreases it is released. This change is recorded. The exosphere is the final layer of the Earth's atmosphere. It extends way into outer space. The air in the exosphere is very thin, but the temperature is very high, because the Sun's rays shine directly on it. 3. Why is the ozone layer important? The ozone layer is important because it stops harmful ultraviolet rays from the Sun from reaching the Earth. If the rays are allowed through the atmosphere, they can cause severe health problems like skin cancer. Chemicals called CFCs have made a hole in the ozone layer above the North and South Poles. 26 Earth's atmosphere? A The Earth's atmosphere is composed of many gases. Nitrogen is the main gas found in the atmosphere. It accounts for about 78 per cent and oxygen makes up 21 per cent. The remaining one per cent is a combination of carbon dioxide and water vapour. There are also very small amounts of trace gases like neon and helium that go to make up the Earth's atmosphere. Quick Q's: 2. What is the exosphere? Q What are the gases that make up the Long way out The outer layers of the atmosphere extend far into space. Q What is the significance of the troposphere in the weather pattern? A The troposphere is the layer closest Q How many layers does the Earth's atmosphere have? A The Earth's atmosphere is composed of several layers. These include the troposphere and the stratosphere. Each layer is divided according to the temperature and density of air in that layer. to the Earth's surface, and it is here that weather is created. Air in the troposphere rises and falls, helping to form clouds, rain and snow. This layer stretches about 8–14.5 kilometres (5–9 miles) above sea level. A warm blanket The Earth is protected by layers of gases. SOHO sends information about these layers back to Earth. Reflected radiation by atmosphere Reflected radiation by Earth's surface Infrared radiation emitted by Earth Absorbed radiation GrBigBk_Q_A 026-041.qxd 21/5/07 12:15 pm Page 27 Earth's Atmosphere When the Earth gets hotter The atmosphere protects us from the Sun's heat by reflecting a lot of it back into space. However, some gases in the atmosphere trap some of this heat, keeping the Earth warm even at night. This process is called the greenhouse effect and the gases that cause it are known as greenhouse gases. These gases include water vapour, carbon dioxide, and CFCs. Humans are adding carbon dioxide and CFCs to the atmosphere all the time. Too much heat is being trapped, and the Earth is getting warmer. Global warming is leading to the melting of glaciers and polar ice caps and an alarming rise in sea levels. It will change the Earth as we know it. Dangerous additions The pollution of the atmosphere by factories and vehicles is creating a dangerous hole in the protective ozone layer above the Earth and increasing the Earth's temperature. It also makes people fall ill more often. Q How does the stratosphere help us? A The stratosphere is the layer just above the troposphere. It extends upwards from the troposphere to about 50 kilometres (31 miles) above the Earth's surface. Compared to the troposphere which is full of moisture, the stratosphere is dry. The stratosphere contains the ozone layer. Ozone absorbs harmful ultraviolet rays from the sun. Q Is the temperature the same in the different layers of the atmosphere? A The temperature in the troposphere is between -52 and 17 °C (-62 to 62 °F). The temperature in the stratosphere is about -3 °C (26 °F). The next layer up, called the mesosphere, is very cold. The temperature here is as low as 93 °C (-135 °F). In the outer layers of the atmosphere the temperature starts to rise again, because there is more heat from the Sun. Temperatures in the outer layer can be as high as 1,727 °C (3,140 °F). Try these too… South Pole Expanding hole Seasons and Climate (28-29), Origin of Life (88-89), The Poles – The Arctic and Antarctica (122-123), Light (180181), Communication and Satellites (192-193) A hole above our heads For over 20 years, scientists have noticed an expanding hole (seen here in pink over the South Pole) in the ozone layer above each of the poles. This is due to the increasing use of chemicals that go into our refrigerators and aerosol cans. The hole means we have less protection from the ultraviolet rays of the Sun. These harmful rays can cause skin cancer. 27 GrBigBk_Q_A 026-041.qxd 21/5/07 12:15 pm Page 28 Planet Earth Seasons and Climate The Earth not only orbits the Sun, but also rotates on its own axis as it does so. The Earth's axis is in fact tilted – meaning that neither of the Earth's poles faces the Sun directly. This tilted axis is responsible for weather and different climates. Quick Q's: 1. What causes day and night? The Earth turning on its axis is responsible for day and night. At any time, half the Earth faces the Sun, where it is day, and half faces away, where it is night. 2. Does the Sun really rise in the east? The Earth spins in an eastward direction. This makes the Sun appear as if it is rising in the east and setting in the west. 3. Why are days longer in summer and shorter in winter? The angle at which sunlight falls on a particular area determines the length of day and night in that region. During summer the Sun stays above the horizon longer, making the days longer. 4. What is the Coriolis effect? The wind moves to the right in the northern hemisphere and to the left in the southern hemisphere. This is called the Coriolis effect. It is caused by the Earth's rotation. It is mainly responsible for thunderstorms and hurricanes. 28 Q How is weather different from climate? A Sunlight falls at varying angles onto the Earth's surface, heating up each of its regions differently. The difference in temperature eventually leads to different types of weather. A climate is when particular weather conditions prevail in a place for an extended period of time. So we can talk about the weather tomorrow or this month, but when we talk of climate we are talking of much longer time periods – decades or even centuries. Q What is a season? A Each season is a period within a year defined by distinct weather. The tilt in the Earth's axis is responsible for seasons. In temperate and polar regions four seasons are recognized – spring, summer, autumn and winter. Some tropical and subtropical regions have a rainy season (sometimes called a monsoon season) and a dry season, while others have hot, rainy and cool seasons. Q What are the factors that influence weather on the Earth? A Temperature, rainfall, wind, cloud and atmospheric pressure are the main factors that influence weather patterns across the world. Wind is caused by the unequal heating of the Earth's surface. When the air above a certain region becomes warm and light, it rises and the heavier cool air sweeps across from another area to take its place. This movement of air is called wind. Atmospheric pressure also affects the movement of wind, which always flows from a region of high pressure to that of low pressure. The difference in pressure between the two areas determines the speed with which the wind blows. If there is a small difference, we feel a breeze. If the difference is large, it leads to a storm. If the wind is flowing over a large water body such as a sea, it can pick up moisture and carry clouds and rain with it. Low pressure usually means stormy weather and rain, while high pressure usually means lots of sun and not much wind. There are other factors, such as the ocean currents created by the Earth's rotation, which also influence weather. The blowing wind The wind always blows from an area of high pressure to an area of low pressure. GrBigBk_Q_A 026-041.qxd 21/5/07 12:15 pm Page 29 Seasons and Climate Q How are clouds formed? A The Sun's heat causes water in the Water stored in Snow melts ice and snow down to Precipitation streams oceans, rivers and lakes to evaporate and form water vapour. The warm water vapour rises upwards, and as it rises, it cools down. As a result, the water vapour in the air condenses to form clouds containing tiny droplets of water. These droplets grow larger in size and finally fall down as rain. Sometimes, the temperature is so low that these droplets freeze into ice crystals and fall down as snow. Condensation Water stored in the atmosphere Transpiration Evaporation Water stored in oceans The water cycle All the water in the Earth's atmosphere, both on its surface and underground, is a part of the water cycle. The water is recycled again and again. Solstices and equinoxes Cold places The closer you are to the North or South Pole, the colder it is. Some animals have adapted so they can survive in the freezing temperatures. Q Which is the place on the Earth that has the coldest climate? A The climate of Antarctica is the coldest on Earth. Nearly all of Antarctica is covered with an ice sheet about 2.5 kilometres thick. The lowest temperature recorded on this continent is -89.6 °C (-128.56 °F) at Vostok research station at the centre of the East Antarctic Ice Sheet. In the northern hemisphere the longest day falls during the summer, on 21 June, when the northern half of the Earth is tipped towards the Sun. This is known as the summer solstice. In the extreme north the Sun does not set at all during this period. During the winter solstice (22 December), the northern part of the Earth is tipped away from the Sun, resulting in the longest night of the year. On 23 September and 21 March the Earth is positioned in such a way that the length of day and night is equal (12 hours each). These days are known as the autumnal and spring equinoxes respectively. Try these too… Earth's Atmosphere (26–27), Plant Life (96–97), South America (112–113), Australia and Oceania (114–115), Africa (118–119), Asia (120–121), The Poles – The Arctic and Antarctica (122–123), Scientific Revolution (150–151) 29 GrBigBk_Q_A 026-041.qxd 21/5/07 12:15 pm Page 30 Planet Earth Mountains, Valleys and Caves Mountains are formed when two of the continental plates that make up the Earth's crust collide. The force caused by the collision pushes both plates (also called tectonic plates) upwards, creating a mountain. Valleys and caves are also natural features created by erosion and the movement of the Earth's crust. Q Can we live on mountains? A It is not easy to live on high mountains. Quick Q's: The weather is extremely cold and not suitable for farming. At very high altitudes, oxygen levels are so low that it becomes difficult to breathe without an oxygen tank and mask. 1. Which is the highest mountain peak in the world? Q How are mountains different Climbing mountains Scientists climb mountains to study them. At a height of about 8,848 metres (29,028 feet) above sea level, Mount Everest is the highest peak in the world. It is a part of the Himalayan mountain range that was formed about 10–15 million years ago. 2. How big is the Grand Canyon? The Grand Canyon is about 446 kilometres (277 miles) long and roughly 1.6 kilometres (1 mile) deep. It is made up of several layers of rock, each one older than the one above it. 3. How are glacial valleys formed? When glaciers slowly flow downhill, they collect many pieces of rock on the way. These pieces scrape against the valley floor, digging deeper into it, until a U-shaped valley is formed. 30 Q How is a valley formed? A A valley is a low-lying area of land that is usually found at the foot of mountains or hills. The most common way valleys are formed is by the erosion of land from running water. River valleys are formed by the action of the river. As a river flows downhill, it cuts through the land like a knife. Over thousands of years the river erodes the land to form a valley, usually in the shape of a V. In contrast, valleys formed by glaciers are often U-shaped, because they are formed by rocks carried in the glacier that erode the soil. Plate 1 Mountains Plate 2 from plateaus? A Like a mountain, a plateau is higher than its surrounding area. However, plateaus have a flat top, while mountains have peaks. Like mountains, plateaus are formed when two continental plates collide, but erosion due to wind and water flattens the top. Plateaus are not as tall as mountains. In fact, some plateaus, such as the Tibetan Plateau, lie between two mountain ranges. Forming a mountain Mountains are formed when two of the Earth's tectonic plates collide. The crust is forced up between the two plates, giving birth to the mountain range. U-shaped valley Glaciers carry stones that scour out the soil, forming U-shaped valleys. Rivers, in contrast, usually form V-shaped valleys. Q What is a canyon? A A deep valley with cliffs on both sides is called a canyon. Sometimes a large river may run through a canyon. The Grand Canyon in Arizona, USA is the world's largest canyon. It was formed by the Colorado River. Millions of years ago, this region was covered by sea. Slowly, a part of the sea floor was pushed up to form a plateau. Over the years, rainwater collected to form a river. This river cut into the rocks on the plateau to form the canyon. GrBigBk_Q_A 026-041.qxd 21/5/07 12:15 pm Page 31 Mountains, Valleys and Caves Caves of lava When volcanoes erupt, lava flows down the side of the volcano. The surface of the lava cools and becomes solid, while hot lava continues to flow underneath it. Once the eruption is over, there is a hollow tube, or cave, left behind underneath the hard crust of lava. Q What are caves? A Caves are huge holes under the ground, in cliffs or under the sea. Caves can be formed in many ways. Most rock caves, especially limestone caves, are formed by rainwater that seeps into tiny cracks in the rocks. The rainwater contains minerals and chemicals that slowly causes the rock to dissolve, leaving behind a large hole. This process may take several thousand, or even a few million years. Q How are sea caves formed? A Sea caves are formed by waves that wear away the rocks at the base of a cliff. These rocks are usually very weak and have tiny cracks in them. The continuous pounding of the waves causes the tiny cracks to widen and soon the rocks begin to crumble and form small hollows. These hollows keep expanding as sand, gravel and rocks brought by the waves erode their inner walls. Some sea caves are submerged during high tide and can only be seen when the water goes down at low tide. Q What is a rift valley? A A rift valley is created when two tectonic plates pull away from each other, leaving a low space in the middle. The Great Rift Valley is the best known rift valley in the world. It covers a distance of over 6,000 kilometres (3,700 miles), stretching from northern Syria in West Asia to central Mozambique in East Africa. It began to form about 35 million years ago, when the African and Arabian tectonic plates began to pull apart. Even today it is still growing, as East Africa slowly separates from the rest of Africa. Rift in the Earth When two of the Earth's plates move away from each other, the soil covering them falls down and forms a rift valley. The rift valleys in East Africa now form a series of lakes. Normal Faults Sea cave Sea caves are most common in areas where the rocks on the coast are soft. Try these too… Other Landforms (32–33), Volcanoes (36–37), Earthquakes and Tsunamis (38–39), South America (112–113), Australia and Oceania (114–115), Africa (118–119), Asia (120–121) Earth's Crust Mantle 31 GrBigBk_Q_A 026-041.qxd 21/5/07 12:15 pm Page 32 Planet Earth Other Landforms Rivers, lakes and streams are natural bodies of water that are found across the world. When it rains or when snow on mountains melts, the water flows down the slopes, forming streams. Several streams join together to form a river. Small rivers drain into larger rivers. The water in rivers keeps flowing until it reaches the sea, though a few rivers hit very dry desert land and dry up. Quick Q's: 1. Which is the largest freshwater lake in the world? Lake Superior, one of the Great Lakes of North America, is the largest freshwater lake in the world. This lake is over 560 kilometres (350 miles) long and about 257 kilometres (160 miles) wide. 2. What is the Sahara known for? The Sahara is the largest hot desert in the world. Located in Africa, it spreads across Mauritania, Morocco, Mali, Algeria, Tunisia, Niger, Libya, Chad, Egypt, Sudan and Eritrea. 3. Which is the longest river? The Nile is the longest river on Earth. It flows for 6,695 kilometres (4,184 miles). 4. Why is Lake Baikal special? Lake Baikal in southern Siberia is the deepest lake in the world, with a maximum depth of 1,637 metres (5,371 feet). It has been around for almost 30 million years. 32 Largest freshwater lake Lake Superior in North America is the largest freshwater lake in the world by area and the third largest by volume. Q How are lakes formed? A Sometimes, rainwater collects in big hollows in the ground to form lakes. These hollows can be formed by the movement of the plates that make up the Earth's crust, or by moving glaciers. Lakes are also formed by landslides that leave huge depressions in the ground. Most lakes and rivers contain freshwater. In places containing a large amount of salt, lake water can be salty. View from space This photograph, taken from an artificial satellite, shows Lake Baikal in southern Siberia. The size of the lake has been reduced in recent years, as more and more of its water is taken away for irrigation. It is considered to be one of the most serious problems in the region. Q What are waterfalls? A Sometimes the surface over which a river flows drops suddenly. Then the water flows over to form a waterfall. There are different kinds of waterfalls. A cascade waterfall flows down a series of natural rock steps. There are no steps in a free-falling waterfall. In a fan waterfall, the water spreads out as it falls down. Angel Falls in Venezuela is the highest free-falling waterfall in the world. The water falls 807 metres (2,648 feet) without any interruption. Often, the sunlight falling over a waterfall creates a rainbow. Q Do rivers flood? A Yes, they do. Rivers often overflow their banks and flood the land around them. This can happen when there has been a lot of rain or a lot of snow has melted in the mountain where the river starts its journey. Floods are often very destructive. They can damage crops and houses and kill people. But in the long run they can also do some good. They bring fresh soil down the river and spread it on the flooded land. Egyptian farmers have been dependent on the annual flooding of the Nile for thousands of years. The Amazon and the Ganges rivers regularly bring fertile soil to the agricultural areas downstream. Longest river The ancient civilization of Egypt started along the banks of the Nile. GrBigBk_Q_A 026-041.qxd 21/5/07 12:15 pm Page 33 Other Landforms Try these too… North America (110–111), South America (112–113), Australia and Oceania (114–115), Europe (116–117) Largest desert The Sahara is the world's largest hot desert. It spreads right across northern Africa from the Atlantic Ocean in the west to the Red Sea in the east. Sand and rock cover most of the dry Sahara, but there are oases where people have lived for centuries. Q What is a desert? A A desert is a dry region with very little rainfall. During the day, temperatures can rise above 50 °C (122 °F). However, nights in a desert can be extremely cold. Most deserts are covered with sand and rocks. Animals and plants that live in this habitat are specially adapted to life with little water and extreme changes in temperature. Cold desert Most deserts are hot during the day, but some deserts are in the coldest parts of the Earth. Some cold deserts are covered in ice throughout the year, allowing very few plants to grow. Cold deserts are also not very suitable for animals. Few species can survive such extreme cold for long periods of time. Antarctica is the largest cold desert in the world. Patagonia in the southernmost part of South America and Gobi in Mongolia are also cold deserts. Q What are montane deserts? A Some deserts, located at very high altitudes, are known as montane deserts. They are common in the Himalayas. Some, like the Tibetan Plateau, are relatively flat. Very few animals can survive the extreme cold and dryness, but the yak lives in Tibet. Q What is an oasis? A For most part deserts are dry and have no water bodies. However, small springs with trees and plants growing around them can be found in certain places. These isolated regions are called oases. An oasis is vital for all forms of life in the desert. 33 GrBigBk_Q_A 026-041.qxd 21/5/07 12:15 pm Page 34 Planet Earth Oceans Arctic Ocean Oceans occupy about 70 per cent of the Earth's surface. There are five oceans in the world. They are the Atlantic, Pacific, Indian, Arctic and Antarctic oceans. The surface under the oceans is called the ocean floor. Like land, the ocean floor also has natural features like plains, valleys and mountains. Atlantic Ocean Indian Ocean Pacific Ocean Antarctic Ocean Quick Q's: Q Which ocean is also known as the 1. Which is the largest of all oceans? Southern Ocean? The Pacific Ocean is the world's largest and deepest ocean. It has an average depth of over 4,000 metres (13,100 feet). It has the world's deepest trench – the Mariana Trench near Japan. The Challenger Deep in the Mariana Trench is the deepest point on Earth – about 11,033 metres (36,200 feet) deep. A 2. What causes an ocean current? An ocean current is a mass of water that keeps moving in one direction. Surface currents are caused by wind and the Earth's rotation. Underwater currents are the result of differences in temperature and salt content of the water. 3. What is a black smoker? When water seeps into the crust of the ocean floor through cracks, it may be heated by the magma below. As pressure builds up within the crust, the hot water shoots up through these cracks. These jets of warm water are often black due to their mineral content, so they are called black smokers. The Antarctic Ocean is also called the Southern Ocean. Until recently, the Antarctic Ocean was considered to be a part of the other main oceans, as it was actually formed from parts of the Pacific, Atlantic and Indian oceans. In the year 2000, however, it was officially named the 'Southern Ocean'. Island Arc Q What is the ocean floor like? A The ocean floor is far from flat. The edges of islands and continents gently slope into the surrounding water to form an area called a continental shelf that is higher than rest of the ocean floor. A continental shelf usually extends about 75 kilometres (47 miles) out to sea but some, like the Siberian shelf in the Arctic Ocean, can extend up to 1,500 kilometres (932 miles). The continental shelf contains large deposits of petroleum, natural gas and minerals. It also receives the most sunlight, so marine life thrives here. The point where the continental shelf starts to plunge steeply towards the deep ocean floor is called the continental slope. It is here that the deep canyons of the ocean are found. N. Equatorial N. Equatorial N. Equatorial S. Equatorial S. Equatorial S. Equatorial West Wind Drift 34 Oceans of the world The five oceans of the world cover over 70 per cent of the surface of the Earth. Active Volcano Oceanic Trench Not a flat floor The ocean floor has mountains and valleys. Some of the mountains are tall enough to rise above the surface and form islands. Q What causes the formation of mountains and valleys on the ocean floor? A Like the rest of the Earth, the ocean floor is divided into tectonic plates. The movement of these plates is responsible for features like ridges, trenches, and valleys. Ridges are formed when two plates drift apart. Boiling rock from inside the Earth, called magma, oozes out through the cracks between the plates and cools to form a ridge. Trenches are formed when a heavier plate sinks down under a lighter one. Ocean currents The water in the oceans and seas is always in motion, due to the rotation of the Earth, the gravitational pull of the Sun and Moon, and the difference in temperature and salt content of the water. These movements form strong currents in the oceans, both at the surface and deep down. GrBigBk_Q_A 026-041.qxd 21/5/07 12:15 pm Page 35 Oceans Q What is a mid-ocean ridge? A The ridges on the ocean floor are Q How are waves different from tides? A Waves are caused by wind, while tides connected to form a single chain called a mid-ocean ridge. The mid-ocean ridge is over 80,000 kilometres (50,000 miles) long and is the longest mountain chain on Earth. On average, these mountains lie about 2,500 metres (8,200 feet) below the ocean surface, with their peaks sometimes breaking above. are the regular rise and fall of the ocean's surface caused by the gravitational pull of the Sun and the Moon on the water that is in the ocean. Waves are formed when winds blow over the surface of the ocean. Stronger winds create larger waves. The water in a wave normally moves in circles. As a wave approaches the land it is slowed down by the rising slope of the seabed. But it is the bottom portion of the wave that is slowed down. The top part of the wave keeps moving and crashes on to the shore as a breaker. North American Plate Eurasian Plate Iceland Atlantic Ocean Mid-Atlantic Ridge Mountains down there The mid-ocean ridge exists on the floor of all the oceans in the world. The diagram shows a part of the mid-Atlantic ridge, which extends below Iceland. Many volcanoes lie along the ridge. Q How are volcanic islands formed? A Volcanoes under the sea are responsible for the formation of volcanic islands. As magma keeps oozing out of a volcano, it can collect, causing the volcano to grow and rise above the ocean surface as an island. Q What is special about the Hawaiian Beach Try these too… Volcanoes (36–37), Earthquakes and Tsunamis (38–39), Hurricanes and Tornadoes (40–41), Whales (56–57), Seabirds (60), Sharks and Rays (68–69), Life of a Fish (70–71), Electricity (186–187) The breaker Breakers are higher when the seabed slopes down quickly from the shore. The beaches of Hawaii and Australia are famous for their high breakers. Surf Deep water Feeling the heat The temperature of the water from an underwater hot spring can be as high as 400 °C (752 °F). However, this water is rich in minerals, helping some unusual creatures like giant tubeworms and eyeless shrimps survive in an environment where nothing else can live. group of islands? A Volcanic activity does not always take place near plate boundaries. There are some places deep inside the Earth that are much hotter than others. As a result, there is constant volcanic activity above these spots, known as hot spots. This activity leads to the formation of underwater volcanoes. The constant movement of tectonic plates eventually shifts the volcano away from the hot spot. Soon, another volcano is created in the area near the hot spot. This often leads to the formation of a chain of islands, such as the Hawaiian Islands. 35 GrBigBk_Q_A 026-041.qxd 21/5/07 12:15 pm Page 36 Planet Earth Volcanoes A volcano is a mountain through which molten rock and gases erupt from the Earth's crust. Volcanoes are named after the Roman god of fire, Vulcan. Q How are volcanoes formed? A Volcanoes are formed by tectonic plates Volcanic rocks Hardened lava from volcanoes forms new rocks. Quick Q's: 1. Which is the highest volcano on Earth? Mauna Loa in Hawaii is the highest volcano on Earth. It rises about 4 kilometres above sea level; below that, it extends to 5 kilometres down before it reaches the seabed. Its massive weight has pushed the volcano down a further 8 kilometres below the seabed! So Mauna Loa is 17 kilometres (56,000 feet) from its base to its summit. 2. Which is the most active volcano? colliding with each other. The heavier plate is usually forced down below the lighter one, where part of it is melted by the heat of the crash. The melting plate forms magma or molten rock that collects below the surface of the Earth in magma chambers. As the amount of magma increases, the pressure inside the chamber rises. This creates a mountain, or volcano. The volcano has a cone, from which gases and lava may trickle out. When the pressure gets too high, the whole chamber explodes, ejecting the magma. This is a volcanic eruption. Continental Crust Oceanic Crust Mantle Mount St Helens in Washington State of USA is the most active volcano. It last erupted in 1980. Movements of the Earth The tectonic plates that cover the Earth can move in various ways, and are constantly rubbing against one another, sometimes violently. 3. What are geysers? Q What are the various things that happen Geysers are jets of hot water that erupt from the Earth. When water trickles down into the hot molten rock under the Earth's crust, it is heated up. As the water becomes hotter, the pressure builds up, finally causing it to spurt out. 36 during a volcanic eruption? A Magma, or molten rock, erupts through the surface of Earth during an eruption. Magma that comes out is called lava. It can be thick and slow moving or thin and fast. Pieces of rocks and ash also erupt from the volcano. Pumice stone, a light rock full of air bubbles, is formed in an explosive volcanic eruption. These volcanic materials are called pyroclasts. Hot water Old Faithful is a geyser of hot water in the Yellowstone National Park, USA. It erupts from the Earth every 90 minutes, on average. Q Do volcanoes erupt regularly? A Volcanoes may be active, intermittent, dormant or extinct depending on how often they erupt. Active volcanoes erupt often. Intermittent volcanoes erupt at regular intervals. Dormant volcanoes have been inactive for a long time. They are the most dangerous because they are merely 'sleeping' and can erupt without warning. Extinct volcanoes have not erupted for thousands of years. It is difficult to distinguish between dormant and extinct volcanoes because some volcanoes may remain quiet for a long time before suddenly becoming active again. Active volcano Mount St Helens is the most active volcano in the world. It last erupted in 1980. GrBigBk_Q_A 026-041.qxd 21/5/07 12:15 pm Page 37 Volcanoes Q What are the different types of volcanoes on the Earth? A Volcanoes are classified according to their shapes and the type of material they are composed of. A shield volcano is a gentle sloping volcano that has long-lasting, gentle eruptions. Most of the volcanoes in the Hawaiian islands are shield volcanoes. A strato volcano is a steep volcano shaped like a cone. When it erupts, it emits gases, ash, pumice and lava. These volcanic eruptions are accompanied by deadly mudflows, making strato volcanoes the most dangerous among the volcanoes on Earth. Famous strato volcanoes include Mount Vesuvius in Italy and Mount Fuji in Japan. Ring of Fire Q What is the 'ring of fire'? A The area encircling the Pacific Ocean is called the ring of fire because most of the Earth's active volcanoes are located in a ring around it. The massive Pacific plate is expanding continuously at the edges of the ocean and hitting the other smaller plates next to it. The collisions cause frequent volcanic activity and earthquakes. The ring of fire stretches from New Zealand, along the eastern coastline of Asia and along the western coast of North and South America. Ring of fire The ring of fire around the Pacific Ocean has been responsible for some of the most destructive volcanic eruptions and earthquakes in human history, including the 1906 San Francisco earthquake and the 1995 earthquake in Kobe, Japan. The biggest earthquake ever recorded was also in the ring of fire – the Great Chilean earthquake of 1960, 9.5 on the Richter scale. Try these too… The Hot Planet (14), The Red Planet (16), Oceans (34–35), Origin of Life (88–89), Dinosaurs (90), North America (110–111), South America (112–113), Australia and Oceania (114–115), Europe (116–117), Africa (118–119), Asia (120–121), The Poles – The Arctic and Antarctica (122–123), Ancient Americas (132) An island disappears The cone shape The cone-shaped volcano, known as a strato volcano, may be the most famous, but is only one of many types of volcanoes. One of the largest volcanic eruptions recorded in recent history occurred on the island of Krakatau in Indonesia in 1883. The eruption was so massive that most of the island disappeared into the sea (pale blue area between the two small islands). Over much of the world, the sky was dark with ash for days. Q Are there volcanoes under the sea? A Volcanoes form under the sea in the same way as on land. When two oceanic plates collide, one may get pushed under the other. The heat generated by the crash causes one plate to melt and form magma. The hot magma rises and forms an underwater volcano, just as it does on land. The Vailulu volcano in Ta'u Island in the Pacific Ocean is an underwater volcano. 37 GrBigBk_Q_A 026-041.qxd 21/5/07 12:15 pm Page 38 Planet Earth Earthquakes and Tsunamis The Earth is made up of a boiling hot, liquid centre covered by a crust. This crust is broken into pieces called tectonic plates, which move around, sometimes colliding into each other. These collisions lead to earthquakes, some so small that they are hardly felt. But some earthquakes are so massive that they cause the ground to shake violently, destroying houses and killing people. Quick Q's: 1. Which is the worst earthquake in history? In 1556, an earthquake struck three provinces in China. About 830,000 people were killed in the disaster. It was the worst earthquake in history. 2. Can we predict earthquakes? No, we cannot. The movements of the Earth are too complex for us to be able to predict earthquakes. But we do know the lines along which the Earth's plates meet, so we know the areas that are more likely to have earthquakes. 3. What is liquefaction? Liquefaction is caused by the violent shaking of the ground during an earthquake. Moist soil or sand turns into slurry, like quicksand. This liquid can suck in entire buildings. 4. Is a tsunami the same as a tidal wave? A tsunami is diffeerent from a tidal wave. A tidal wave is generated by high winds, but a tsunami is caused by underwater earthquakes, landslides or volcanic eruptions. 38 Q Do earthquakes occur everywhere? A Earthquakes usually occur along a region called a fault, where broken rocks under the Earth's surface rub against each other and cause tremors. Faults are marked by cracks on the Earth's surface, caused by the movement of tectonic plates. Most faults are located near the edges of the plates, but small faults can be found far away from the boundaries. Q How do faults produce earthquakes? A Faults allow the rock fragments that form the Earth's crust to move about. Over a period of time, plate movement builds up pressure, causing rocks along a fault to bend or break with a jolt. This sudden movement releases energy that moves through the surface of the Earth in the form of waves. This is an earthquake. The energy moves out in a circle from the point where the movement occurs. Fault in the Earth The San Andreas Fault in California, USA, is one of the few faults in the Earth's surface that can actually be seen by any observer on the ground. Most of the other faults are covered by soil or water. These faults mark the lines on the Earth's surface where two tectonic plates of the Earth meet. As a result, areas around these faults are the ones most prone to volcanic activity and earthquakes. San Francisco 1906 The notorious San Francisco earthquake in 1906 destroyed most of the large buildings in the city. Tramlines were ripped up as the roads buckled under them. Q Where is an earthquake most dangerous? A The point inside the Earth where the rocks first begin to break is the focus of the earthquake. The point on the Earth's surface that lies directly above the focus is called the 'epicentre'. This is where the earthquake is strongest. In a major earthquake, the maximum damage takes place at the epicentre, and there is less damage as you get further away from it. The epicentre is directly above the hypocentre, the actual location of the energy released inside the Earth. Seismic waves ripple out from the hypocentre. After an earthquake, scientists can find the centre by looking at the seismic wave data from three separate locations. The extent of the damage caused by an earthquake may also depend on the nature of the soil. GrBigBk_Q_A 026-041.qxd 21/5/07 12:15 pm Page 39 Earthquakes and Tsunamis Q Do earthquakes occur only on land? A Earthquakes also occur under the ocean. Sometimes, massive earthquakes that start on the ocean floor can create giant, destructive waves called tsunamis. These waves move at great speeds (up to about 800 kilometres or 500 miles per hour) and can travel thousands of kilometres across the ocean. In deep water, the waves are not very high. They gain strength and height as they approach the shore. Tsunamis can be about 30 metres (98 feet) high. These huge waves break on to the shore with a great deal of force, bringing down trees and large buildings. When disaster strikes On 26 December 2004, a tsunami spread across the Indian Ocean, killing over 250,000 people. The tsunami was caused by an underwater earthquake that occurred near the island of Sumatra, Indonesia. The tsunami hit the coasts of about 15 countries. Its effect was felt even in the southern tip of Africa, about 8,500 kilometres (5,300 miles) away from the epicentre of the earthquake! Before After Q Do earthquakes cause destruction every time they occur? A Some earthquakes are extremely destructive. A strong quake can topple buildings and bridges, trapping people underneath them. If gas pipes and electrical wires break, they can start fires that rage for several days. Earthquakes can also cause landslides and avalanches. The violent shaking of the Earth sometimes loosens chunks of snow or mud that slide down the slopes of mountains and hills, burying houses and people under them. Q Can an earthquake be measured? A Earthquakes are measured using the Richter scale. It was developed in 1935 by Charles Richter and Beno Gutenberg at the California Institute of Technology. This scale uses numbers from 1 to 10 to measure the intensity of an earthquake. Each increase of one point on the scale means a ten-fold increase in the strength of the earthquake. So a level 5.0 earthquake is ten times stronger than a level 4.0 earthquake. The Richter scale works by measuring vibrations around the epicentre of an earthquake. Earthquake effect An earthquake can lead to a deadly avalanche or a landslide that can cause more damage than the original earthquake. Old instrument The ancient Chinese invented an instrument that reacted to tremors in the Earth – a ball dropped from the mouth of the dragon into the mouth of a frog, warning people about a possible earthquake. Try these too… The Hot Planet (14), Mountains, Valleys and Caves (30–31), Oceans (34–35), Volcanoes (36–37), North America (110–111), South America (112–113), Australia and Oceania (114–115) 39 GrBigBk_Q_A 026-041.qxd 21/5/07 12:15 pm Page 40 Planet Earth Hurricanes and Tornadoes Sometimes the weather becomes wild. Blizzards, thunderstorms, hurricanes and heatwaves are some examples of extreme weather conditions. Such severe weather often causes a great deal of damage to both life and property. Hurricanes and tornadoes especially are very destructive. Quick Q's: 1. Can hurricane winds be measured? Hurricanes are divided into five categories depending on their wind speeds. Category 5 hurricanes are the worst, causing maximum damage. Winds of a category 5 hurricane can reach speeds of about 250 kilometres per hour (155 miles per hour). Category 1 hurricanes are much weaker, and only travel at 119–153 kilometres per hour (74–95 miles per hour). Q What is a hurricane? A Hurricanes are large, violent storms that form over the ocean near the equator. These storms are accompanied by winds that travel at an average speed of about 119 kilometres per hour (74 miles per hour). Hurricanes usually occur between June and November. 3. What is the Fujita scale? The Fujita scale is used to measure the intensity of a tornado. It ranks tornadoes by the damage caused to man-made structures. 4. How did tornadoes get their name? The word tornado is from the Spanish tomear, meaning 'to turn'. 40 rises, creating an area of low pressure. Cooler wind moves in to take place of the warm air. The Earth's rotation causes the rising hot air to twist and form a cylinder. As the warm air rises higher, it cools down and forms huge thunderclouds and finally becomes a hurricane. Meanwhile, the cooler air at the bottom also becomes warm, adding more energy to the storm. Q What is the eye of a hurricane? A The centre of a hurricane is called the eye. The eye is an area of clear skies, light winds and no rain. It is also the warmest part of the storm and is surrounded by a wall of heavy rain and strong winds. People faced with a hurricane usually experience the heavy rain and strong winds first, then there is a period of calm as the eye passes over the area, followed by more stormy weather. 2. What is a storm surge? Sometimes the strong winds of a hurricane can cause the water level in the ocean to rise. Huge waves hit the coast along with the storm, causing severe flooding. This is called a storm surge. Q How does a hurricane form? A When the air above the sea is heated it Eye of the hurricane This satellite image clearly shows the eye of the hurricane, an area of calm in the middle of the storm. Huge destroyer In 2005, Hurricane Katrina, seen here in a satellite image, destroyed large parts of the city of New Orleans in the USA. GrBigBk_Q_A 026-041.qxd 21/5/07 12:15 pm Page 41 Hurricanes and Tornadoes Q What is the worst hurricane on record? A The hurricane that ripped through the Caribbean islands of Martinique, St. Eustatius and Barbados in October 1780 is the worst on record so far. It killed nearly 22,000 people. However, this hurricane does not have a name, because the practice of giving human names to major hurricanes started during World War II. Air Current Chasing the storm Most of us would prefer to stay as far away as possible from all violent storms, especially hurricanes and tornadoes. Some people however, chase hurricanes and tornadoes. For these people, confronting a storm is exciting. Storm chasers use special equipment to locate and follow storms. They usually have a well-equipped vehicle fitted with the latest technology, including cameras, radios, scanners and first-aid kits. The videos, photographs and all other data collected by storm chasers have helped scientists understand hurricanes and tornadoes better. Water Spout The making of a storm Warm air rises from the sea, taking water with it in the form of a funnel, and starting a storm. Q What is a tornado? A A tornado is a black, funnel-shaped storm that is highly destructive. These storms usually form where cold polar winds mix with warm, moist tropical winds. They start as rotating thunderstorms called supercells. Gradually the spinning wind in the supercell forms the funnel of a tornado. The wind in the funnel spins so fast that it sucks objects into it like a vacuum cleaner. Q What is Tornado Alley? A Tornado Alley is an area that extends across the Great Plains of the USA, from central Texas in the south to the border of Canada in the north. The conditions in this region are most suitable for the formation of severe tornadoes, which occur during spring and early summer. Q What is a waterspout? A Tornadoes usually travel across land. However, occasionally, tornadoes pass over water. In these cases, the high-speed winds suck in water, creating tall columns of spinning water called waterspouts. These waterspouts are weaker than land tornadoes and occur in warm tropical oceans. However, they are still strong enough to cause huge damage to any boat or ship caught in them. Waterspout When tornadoes pass over water, they suck the water up into tall spinning columns called waterspouts. Try these too… Seasons and Climate (28–29), Communication and Satellites (192–193), Water Transport (196–197) 41 GrBigBk_Q_A 042-059.qxd 21/5/07 12:14 pm Page 42 The Living Planet Monkeys Monkeys belong to the group of mammals called primates, which also includes apes and humans. All three species share certain characteristics, such as narrow noses and five fingers and toes. However, unlike apes and humans, many monkeys have tails. Monkeys from Asia and Africa have noses that point downwards, while monkeys from Central and South America have broad noses and nostrils that open sideways. Quick Q's: 1. Why is the Japanese macaque also known as the snow monkey? The Japanese macaque, commonly known as the snow monkey, is one of the few primate species that live in cold regions. They are found in the mountains of Honshu in Japan. When it is very cold, these monkeys move near hot springs to keep themselves warm. 2. What is grooming? Monkeys and apes groom each other's fur using their hands. This helps not only to get rid of parasites and dirt but is also an important part of socializing. 3. Why are monkeys called social animals? Most species of monkeys live in groups. The size of a group depends on how much food is available and if there are predators around. 4. Do howler monkeys howl? Howler monkeys make a peculiar barking sound. They can be heard up to 3 kilometres (1.9 miles) away. 42 Q What are the common characteristics of primates? A All primates have a large brain, and their eyes face forwards, allowing binocular vision. Most of them have thumbs on both hands and feet that can be used for grasping. Their highly developed brain helps them to remember things, and to understand others. Q How many primate species are there in the world? A There are more than 350 species of primates in the world, divided into two groups. Small to medium-sized primates, such as lemurs and lorises, have long whiskers and well-developed senses of smell and hearing. The rest of the primates, including humans, apes and other monkeys, are part of the 'humanlike' category. This group consists of about 175 species. Most of these primates have flat faces and a poor sense of smell. Big hug Snow monkeys are often found huddling near hot springs to keep warm. Top of the forest Colobus monkeys are usually found at the top layer of branches in African rainforests. Q What does a monkey eat? A Most monkeys will eat whatever they come across, including birds' eggs, fruit and the sap from plants. Several species of monkey will even attack and eat other monkeys. Howler monkeys of South America and colobus monkeys of Africa eat the leaves of any type of tree. The digestive system of leaf-eating monkeys is similar to that of other herbivores, like deer and cows. Ringed tail Lemurs are easily identified by their ringed tails. GrBigBk_Q_A 042-059.qxd 21/5/07 12:14 pm Page 43 Monkeys Q Why are spider monkeys so called? A A spider monkey is a species of New World monkey (from the American continent) that has long, slender, spidery limbs. It displays great acrobatic skills, using its hands and strong tail to grip branches as it swings through the trees. Spider monkeys only travel on par

subset: commoncrawl