The envelope of gases surrounding the earth's crust is called

Step 1: Analyze the question The question asks for the name of the envelope (layer) of gases around the earth's crust. The key word is "gases."

Step 2: Explain the concepts The "sphere" names in Geography each refer to a different part of the earth:

• Hydrosphere is all the water on Earth: oceans, rivers, lakes, and underground water.
• Barysphere is the heavy, dense interior of the earth, also called the core or centrosphere. It is rich in iron and nickel.
• Atmosphere is the layer of gases (nitrogen about 78%, oxygen about 21%, plus argon, carbon dioxide and others) that surrounds the earth.
• Lithosphere is the solid, rocky outer part of the earth, made up of the crust and the uppermost mantle.

Step 3: Solution We need the layer made of gases that surrounds the crust:

• Hydrosphere is water, so it is not correct.
• Barysphere is the dense interior, so it is not correct.
• Lithosphere is solid rock, so it is not correct.
• Atmosphere is the gaseous envelope, so it is correct.

Answer: C. atmosphere

Exam tip: Use the Greek roots to remember the spheres:

• Atmos = vapour or gas, so atmosphere is gas.
• Hydro = water, so hydrosphere is water.
• Litho = stone, so lithosphere is rock.
• Bary = heavy, so barysphere is the heavy core.