Instruct: Given a question, retrieve relevant documents that answer the question.
Query: When was the Hadean era?
The Hadean () is a geologic eon of the Earth pre-dating the Archean. It began with the formation of the Earth about 4.6 billion years ago and ended, as defined by the ICS, 4 billion years ago. , the ICS describes its status as ""informal"". Geologist Preston Cloud coined the term in 1972, originally to label the period before the earliest-known rocks on Earth. W. Brian Harland later coined an almost synonymous term, the "Priscoan period", from "priscus", the Latin word for "ancient". Other, older texts simply refer to the eon as the Pre-Archean.
The Phanerozoic is the current eon on Earth, which started approximately 542 million years ago. It consists of three eras: The Paleozoic, Mesozoic, and Cenozoic, and is the time when multi-cellular life greatly diversified into almost all the organisms known today.
The Ediacaran Period (), spans 94 million years from the end of the Cryogenian Period 635 million years ago (Mya), to the beginning of the Cambrian Period 541 Mya. It marks the end of the Proterozoic Eon, and the beginning of the Phanerozoic Eon. It is named after the Ediacara Hills of South Australia.
The Phanerozoic Eon is the current eon in the geologic timescale. It covers roughly 541 million years. During this period continents drifted about, eventually collected into a single landmass known as Pangea and then split up into the current continental landmasses.
The Phanerozoic eon began following the Precambrian. The first major unit of time it contained was the Cambrian period of the Paleozoic era. At the time, earth's continents were in a very different arrangement and were generally smaller than they are today. The southeastern part of the US was connected to South America and Africa and located in the polar latitudes of the southern hemisphere. The western states were located near the equator.
Excluding a few contested reports of much older forms from North America and India, the first complex multicellular life forms seem to have appeared at roughly 1500 Ma, in the Mesoproterozoic era of the Proterozoic eon. Fossil evidence from the later Ediacaran period of such complex life comes from the Lantian formation, at least 580 million years ago. A very diverse collection of soft-bodied forms is found in a variety of locations worldwide and date to between 635 and 542 Ma. These are referred to as Ediacaran or Vendian biota. Hard-shelled creatures appeared toward the end of that time span, marking the beginning of the Phanerozoic eon. By the middle of the following Cambrian period, a very diverse fauna is recorded in the Burgess Shale, including some which may represent stem groups of modern taxa. The increase in diversity of lifeforms during the early Cambrian is called the Cambrian explosion of life.
The Paleozoic (or Palaeozoic) Era (; from the Greek "palaios" (παλαιός), "old" and "zoe" (ζωή), "life", meaning "ancient life") is the earliest of three geologic eras of the Phanerozoic Eon. It is the longest of the Phanerozoic eras, lasting from , and is subdivided into six geologic periods (from oldest to youngest): the Cambrian, Ordovician, Silurian, Devonian, Carboniferous, and Permian. The Paleozoic comes after the Neoproterozoic Era of the Proterozoic Eon and is followed by the Mesozoic Era.
In large-scale natural science, there is need for another time perspective, independent from human activity, and indeed spanning a far longer period (mainly prehistoric), where "geologic era" refers to well-defined time spans. 
The next-larger division of geologic time is the eon. The Phanerozoic Eon is subdivided into eras. There are currently three eras defined in the Phanerozoic; the following table lists them from youngest to oldest (BP is an abbreviation for "before present").
The Precambrian (or Pre-Cambrian, sometimes abbreviated pЄ, or Cryptozoic) is the earliest part of Earth's history, set before the current Phanerozoic Eon. The Precambrian is so named because it preceded the Cambrian, the first period of the Phanerozoic eon, which is named after Cambria, the Latinised name for Wales, where rocks from this age were first studied. The Precambrian accounts for 88% of the Earth's geologic time.
The Cretaceous (, ) is a geologic period and system that spans 79 million years from the end of the Jurassic Period million years ago (mya) to the beginning of the Paleogene Period mya. It is the last period of the Mesozoic Era, and the longest period of the Phanerozoic Eon. The Cretaceous Period is usually abbreviated K, for its German translation "Kreide" (chalk, "creta" in Latin).
The Amazonian is a geologic system and time period on the planet Mars characterized by low rates of meteorite and asteroid impacts and by cold, hyperarid conditions broadly similar to those on Mars today. The transition from the preceding Hesperian period is somewhat poorly defined. The Amazonian is thought to have begun around 3 billion years ago, although error bars on this date are extremely large (~500 million years). The period is sometimes subdivided into the Early, Middle, and Late Amazonian. The Amazonian continues to the present day.
The Cretaceous is the longest period in the Mesozoic, spans from 145 million to 66 million years ago, and is divided into two epochs: Early Cretaceous, and Late Cretaceous.
The Middle Stone Age (or MSA) was a period of African prehistory between the Early Stone Age and the Later Stone Age. It is generally considered to have begun around 280,000 years ago and ended around 50–25,000 years ago. The beginnings of particular MSA stone tools have their origins as far back as 550–500,000 years ago and as such some researchers consider this to be the beginnings of the MSA. The MSA is often mistakenly understood to be synonymous with the Middle Paleolithic of Europe, especially due to their roughly contemporaneous time span, however, the Middle Paleolithic of Europe represents an entirely different hominin population, "Homo neanderthalensis", than the MSA of Africa, which did not have Neanderthal populations. Additionally, current archaeological research in Africa has yielded much evidence to suggest that modern human behavior and cognition was beginning to develop much earlier in Africa during the MSA than it was in Europe during the Middle Paleolithic. The MSA is associated with both anatomically modern humans ("Homo sapiens") as well as archaic "Homo sapiens", sometimes referred to as "Homo helmei". Early physical evidence comes from the Gademotta Formation in Ethiopia, the Kapthurin Formation in Kenya and Kathu Pan in South Africa.
There has been no absolute dating of the Nemegt Formation. It is, however, almost certainly early Maastrichtian c 71-70 Ma. Gradzinski and others considered a Campanian age possible but more recent research indicates otherwise. A Campanian age no longer seems credible, because the Alagteegian (or lower Djadokhtan, at the locality "Chuluut Uul") has been radiometrically dated at about 73.5 Ma or even younger (a more recent K/Ar date is 71.6 +/- 1.6 Ma). The c 73.5 (or perhaps 72) Ma Alagteegian is separated from the Nemegt by the "classic" Djadokhtan (e.g. Bayan Dzag), later Djadohktan (represented by Ukhaa Tolgod) and Barungoyotian (Khulsan). All these intervening horizons almost certainly represent more than the 1.5 million years between the dated Alagteegian level and the onset of Maastrichtian time (72.1 million Ma according to current dating). Ergo the Nemegt is entirely Maastrichtian. See also Shuvalov, Sochava and Martinsson " The Age of Dinosaurs in Russia and Mongolia." The presence of "Saurolophus" further supports an early Maastrichtian age as the same genus occurs in the early Maastrichtian Horseshoe Canyon formation.
The Morrison Formation is a sequence of shallow marine and alluvial sediments which, according to radiometric dating, ranges between 156.3 million years old (Ma) at its base, to 146.8 million years old at the top, which places it in the late Oxfordian, Kimmeridgian, and early Tithonian stages of the Late Jurassic period. This formation is interpreted as a semiarid environment with distinct wet and dry seasons. The Morrison Basin where dinosaurs lived, stretched from New Mexico to Alberta and Saskatchewan, and was formed when the precursors to the Front Range of the Rocky Mountains started pushing up to the west. The deposits from their east-facing drainage basins were carried by streams and rivers and deposited in swampy lowlands, lakes, river channels and floodplains. This formation is similar in age to the Solnhofen Limestone Formation in Germany and the Tendaguru Formation in Tanzania. In 1877 this formation became the center of the Bone Wars, a fossil-collecting rivalry between early paleontologists Othniel Charles Marsh and Edward Drinker Cope.
Argon-argon radiometric dating indicates that the Kaiparowits Formation was deposited between 76.6 and 74.5 million years ago, during the Campanian stage of the Late Cretaceous period. During the Late Cretaceous period, the site of the Kaiparowits Formation was located near the western shore of the Western Interior Seaway, a large inland sea that split North America into two landmasses, Laramidia to the west and Appalachia to the east. The plateau where dinosaurs lived was an ancient floodplain dominated by large channels and abundant wetland peat swamps, ponds and lakes, and was bordered by highlands. The climate was wet and humid, and supported an abundant and diverse range of organisms. This formation contains one of the best and most continuous records of Late Cretaceous terrestrial life in the world.
The Cretaceous () had much of the same insect fauna as the Jurassic until much later on. During the Cretaceous, the late-Paleozoic-to-early-Mesozoic supercontinent of Pangaea completed its tectonic breakup into present day continents, although their positions were substantially different at the time. As the Atlantic Ocean widened, the convergent-margin orogenies that had begun during the Jurassic continued in the North American Cordillera, as the Nevadan orogeny was followed by the Sevier and Laramide orogenies. Though Gondwana was still intact in the beginning of the Cretaceous, it broke up as South America, Antarctica and Australia rifted away from Africa (though India and Madagascar remained attached to each other); thus, the South Atlantic and Indian Oceans were newly formed. Such active rifting lifted great undersea mountain chains along the welts, raising eustatic sea levels worldwide. To the north of Africa the Tethys Sea continued to narrow. Broad shallow seas advanced across central North America (the Western Interior Seaway) and Europe, then receded late in the period, leaving thick marine deposits sandwiched between coal beds.
220,000,000 BC, Late Triassic (Arizona) − This episode follows the evolution of the first dinosaurs and other prehistoric creatures in the late Triassic period.152,000,000 BC, Late Jurassic (Colorado) − This episode follows the story of a young female "Diplodocus" and her brothers and sisters in the late Jurassic period.149,000,000 BC, Late Jurassic (Oxfordshire) − This episode follows the life of several baby "Ophthalmosaurus" and a bull "Liopleurodon" in the late Jurassic period.127,000,000 BC, Early Cretaceous (Brazil) − This episode follows a male "Ornithocheirus" on his long journey to the mating grounds in the early Cretaceous period.106,000,000 BC, Early Cretaceous (Antarctica) − This episode follows the hardships of an Antarctican "Leaellynasaura" clan in the early Cretaceous period.65,500,000 BC, Late Cretaceous (Montana) − This episode follows the final years of the dinosaurs and a mother "Tyrannosaurus rex" and her babies in the late Cretaceous period.49,000,000 BC, Early Eocene (Germany) − This episode follows the life of a mother "Leptictidium" and her babies in the dense forests of Germany in the early Eocene epoch.36,000,000 BC, Late Eocene (Pakistan) − This episode follows the sea journey of a pregnant female "Basilosaurus" search for food in the late Eocene epoch.25,000,000 BC, Late Oligocene (Mongolia) − This episode follows the life of a young "Paraceratherium" and his mother from his birth in the late Oligocene epoch.3,200,000 BC, Late Pliocene (Ethiopia) − This episode follows the hardships of an "Australopithecus" group and a young called Blue in the late Pliocene epoch.1,000,000 BC, Early Pleistocene (Paraguay) − This episode follows a male "Smilodon" called Half-Tooth after he lost his territory in the early Pleistocene epoch.30,000 BC, Late Pleistocene (North Sea, Belgium, and Swiss Alps) − This episode follows a herd of woolly mammoth journey to the Alps in the last Ice Age of the late Pleistocene epoch.This episode details a list of animals from the first season that the developers thought were the most impressive creatures on Earth.
The amount of oxygen in the atmosphere has fluctuated over the last 600 million years, reaching a peak of 35% during the Carboniferous period, significantly higher than today's 21%. Two main processes govern changes in the atmosphere: plants use carbon dioxide from the atmosphere, releasing oxygen and the breakdown of pyrite and volcanic eruptions release sulfur into the atmosphere, which oxidizes and hence reduces the amount of oxygen in the atmosphere. However, volcanic eruptions also release carbon dioxide, which plants can convert to oxygen. The exact cause of the variation of the amount of oxygen in the atmosphere is not known. Periods with much oxygen in the atmosphere are associated with rapid development of animals. Today's atmosphere contains 21% oxygen, which is high enough for rapid development of animals.The climate of the late Precambrian showed some major glaciation events spreading over much of the earth. At this time the continents were bunched up in the Rodinia supercontinent. Massive deposits of tillites and anomalous isotopic signatures are found, which gave rise to the Snowball Earth hypothesis. As the Proterozoic Eon drew to a close, the Earth started to warm up. By the dawn of the Cambrian and the Phanerozoic, life forms were abundant in the Cambrian explosion with average global temperatures of about 22 °C.
The Campanian is, in the ICS' geologic timescale, the fifth of six ages of the Late Cretaceous epoch (or, in chronostratigraphy: the fifth of six stages in the Upper Cretaceous series). The Campanian spans the time from 83.6 ± 0.7 Ma to 72.1 ± 0.6 Ma (million years ago). It is preceded by the Santonian and it is followed by the Maastrichtian.
In the hall representing the Cretaceous period, which is the last period of the Mesozoic era from 145 to 66 million years ago, the displays relate to the biological and social habits of dinosaurs, reasons for their extinction by the end of the Cretaceous period, that are attributed to meteorite, volcanic eruptions and intense geographic and climatic changes. Evolution of birds inferred as theropods evolving from the non-avian dinosaurs are represented by the "Archaeopteryx" (a prehistoric bird) and dinosaurs such as the "Deinonychus" or the "Dromaeosaurus".
Hadean zircon is the oldest-surviving crustal material from the Earth's earliest geological time period, the Hadean eon, about 4 billion years ago. Zircon is a mineral that is commonly used for radiometric dating because it is highly resistant to chemical changes and appears in the form of small crystals or grains in most igneous and metamorphic host rocks.
The Eoarchean (; also spelled Eoarchaean) is the first era of the Archean Eon of the geologic record for which the Earth has a solid crust. It spans 400 million years from the end of the Hadean Eon 4 billion years ago (4000 Mya) to the start of the Paleoarchean Era 3600 Mya. The beginnings of life on Earth have been dated to this era and evidence of cyanobacteria date to 3500 Mya, just outside this era. At that time, the atmosphere was without oxygen and the pressure values ranged from 10 to 100 bar (around 10 to 100 atmospheres).
The Hadean eon represents the time before a reliable (fossil) record of life; it began with the formation of the planet and ended 4.0 billion years ago. The following Archean and Proterozoic eons produced the beginnings of life on Earth and its earliest evolution. The succeeding eon is the Phanerozoic, divided into three eras: the Palaeozoic, an era of arthropods, fishes, and the first life on land; the Mesozoic, which spanned the rise, reign, and climactic extinction of the non-avian dinosaurs; and the Cenozoic, which saw the rise of mammals. Recognizable humans emerged at most 2 million years ago, a vanishingly small period on the geological scale.
In the geologic record the Chaotian eon or era is unofficially proposed to denote the time preceding the solidification of the Earth's crust and the formation of Earth's moon, it is the earliest era within the eon of Hadean. It lasted 196 million years, at to the beginning of the Zirconian era, . It is named after Chaos, the primeval void in Greek mythology. The Chaotian sets in with the emergence of Earth at 4.6 billion years ago. Its upper limit and thus the transition to the Zirconian era is defined by the occurrence of the first conservation capable mineral. These are zircon, the oldest mineral in the Jack Hills of Narryer Gneiss Terrane in Western Australia (Yilgarn craton) found and were dated 4,404 ± 8 million years ago