People who study the Earth – the Earth Scientists – usually talk of four natural realms on the Earth. Realms are areas which have some common features. These are 1. Lithosphere, 2. Hydrosphere, 3. Atmosphere and 4. Biosphere.
You have read much about many of these in the earlier classes but in this chapter, we will see some broad features of these spheres or realms, and how they are interrelated and also how human beings interact with them.1.Lithosphere: It is the solid crust or the hard top part of the Earth. It is made up of rocks and minerals and covered with a thick layer of soil. (In Greek ‘Litho’ means stone or rock and ‘sphaira’ means sphere or ball.) It is not a smooth surface as you see on the globe, but has high mountains, plateaus or high lands, low plains, deep valleys and very deep basins which are filled with water (oceans). Many of these features are shaped by wind and water. Portions of this crust, in the form of dust etc., are mingled with the air too. When the lithosphere heats up due to sunrays or cools down, it influences the air and water too. We and most other living beings live on this realm. We use the rocks and soils and other things found on this hard crust, in many ways.
2. Hydrosphere: The realm of water is called Hydrosphere. (It comes from the Greek word ‘hudor’ meaning water.) Some part of the water is found deep down under the earth among rocks (ground water or mineral water). It comprises of the various sources of water and different types of water bodies like rivers, lakes, seas, oceans etc.3. Atmosphere: The thin layer of air that surrounds the earth is Atmosphere (The Greek word ‘atmos’ means vapour). It consists of a large number of gases including oxygen, nitrogen, carbon dioxide, water vapour etc and dust particles. The Natural Realms of the Earth Lithosphere.
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