Answer:
The correct answer would be a blanket.
Like the blanket keeps us warm, the atmosphere keeps the earth warm.
It is surrounded around the earth as like the blanket around our body.
The atmosphere (mainly greenhouse gases) traps the most of the radiations coming from the sun and the radiations reflected from the surface of the earth and help in maintaining the average temperature of the earth habitable.
In absence of the atmosphere, the average temperature of the earth would have been around -18°C.
