- The surface of the earth is made of 70% ocean
- Most means over 50% of something
- Therefore, most of earth's surface is made of oceans

- Most of earth's surface is made of oceans
- The hydrosphere is a thin layer of water covering the earth 's surface
- So, most of the hydroshpere is made of oceans

- Most of the hydroshpere is made of oceans
- The formation of organic rocks is usually found in the ocean
- Hence, most of the formation of organic rocks in the hydroshpere occurs in the oceans

Hence, most of the formation of organic rocks in the hydroshpere occurs in the oceans
Question
Scientists who have studied the hydrosphere concluded that about 71% of Earth is covered with water. Which part of the hydrosphere is most often associated with the formation of organic rocks?

Context
- The formation of organic rocks is usually found in the ocean 
- The surface of the earth is made of 70% ocean 
- Most means over 50% of something 
- The hydrosphere is a thin layer of water covering the earth 's surface