Which layer is the first major layer of the atmosphere, closest to Earth's surface?

• A. Troposphere
• B. Stratosphere
• C. Mesosphere
• D. Thermosphere

Answer: (A)

Understanding the order of Earth's atmospheric layers from the surface helps you see which layer sits closest to Earth. The layer right above the planet is where weather happens, clouds form, and most of the atmosphere’s mass is found. This is the troposphere, the first major layer. As you go higher, you move into the stratosphere, which contains the ozone layer and where temperature tends to rise with height. Above that is the mesosphere, where temperatures fall with altitude, and then the thermosphere, which is very thin but can have very high temperatures in the sun. Because the troposphere is the lowest layer and holds most of the atmospheric mass, it is the first major layer.