What is the lowest layer of Earth’s atmosphere called?

The troposphere is the lowest layer of Earth’s atmosphere.

It begins at the surface and extends upward to the tropopause. Its average depth is about 8 kilometers near the poles and about 18 kilometers near the equator, although the boundary shifts with season, latitude, and weather conditions.

Most clouds and nearly all ordinary weather occur in the troposphere because it contains most of the atmosphere’s water vapor. Temperature generally decreases with altitude in this layer, allowing rising and sinking air to drive convection and weather systems.

Above the troposphere lies the stratosphere, where temperature generally increases with altitude because ozone absorbs ultraviolet radiation. The tropopause separates these layers, but it is not at one fixed height around the planet.