Answer the following question given this paragraph: 

The troposphere is the lowest layer of the atmosphere. In it, temperature decreases with altitude. The troposphere gets some of its heat directly from the Sun. Most, however, comes from Earth's surface. The surface is heated by the Sun and some of that heat radiates back into the air. This makes the temperature higher near the surface than at higher altitudes.


Q: What do we call the lowest layer of the atmosphere?


A:
troposphere