Part of tge earths atmosphere closest to its surface?
The part of the earth's atmosphere that is closest to its surface is known as the troposphere.
Heat radiation from the Earths core. This heat is rising towards the atmosphere, and bounced back towards the Earths surface, in whats called the Greenhouse Effect. Next to the Earths hot core, the energy that heats Earths atmosphere is heat radiation from the sun. This heat is also being bounced as a part of the Greenhouse Effect.