When energy reaches the Earth, some gets reflected back into space but most is absorbed by the Earth's surface, heating the planet. The Earth, in turn, radiates energy out into space. The type of radiation which is emitted by a blackbody radiator, such as the Earth, depends on the object's temperature. Because the Earth is much cooler than the Sun, it emits energy at a lower frequency: in the thermal infrared (IR) region.

Open the Earth's Radiation Balance learning tool and click on the bottom, left hand panel entitled "Earth's Emission of Thermal Radiation."

Take care to work through the visualization and thoroughly understand the answers to each of the questions posed:

1. 70% of incoming energy from the sun is absorbed by the earth. What happens to this energy?
2. How do infrared radiation and visible light differ in terms of wavelength and energy?
3. What are some reasons for the drastic differences between the climate on Mars and on Earth?