If there will be no atmosphere the temperature of the earth increases in the day and decreases in the night. The atmosphere helps to trap the radiation in the earth atmosphere with the help of the greenhouse. During the day sunlight comes to the earth surface the planet, heats up. As the surface gets warmer it radiates infrared heat back into space. Once the heat radiated by the surface is equal to the sunlight being absorbed by it the surface stops heating up, and temperatures remain relatively stable. However, once the Sun sets down there is no sunlight reaching the surface and the surface of the planet cools as it radiates heat into space. Thus the correct answer is Option C.