What is the basis for dividing the atmosphere into four layers?

The atmosphere is divided into four main layers based on changes in temperature and composition. These layers are known as the troposphere, stratosphere, mesosphere, and thermosphere.

1. Troposphere: This is the lowest layer of the atmosphere, extending from the Earth's surface up to an altitude of about 8-15 kilometers (5-9 miles). The troposphere contains almost all of the Earth's weather phenomena, such as clouds, rain, and storms. Temperature generally decreases with increasing altitude in this layer.

2. Stratosphere: The stratosphere is located above the troposphere and extends up to around 50 kilometers (30 miles) above the Earth's surface. In this layer, the temperature remains fairly constant or slightly increases with altitude. The stratosphere contains the ozone layer, which absorbs and blocks harmful ultraviolet radiation from the Sun.

3. Mesosphere: Above the stratosphere lies the mesosphere, which extends up to an altitude of approximately 80-85 kilometers (50-53 miles). The temperature in this layer decreases with increasing altitude, marking the coldest temperatures in the atmosphere. The mesosphere is also where meteors burn up upon entering the Earth's atmosphere.

4. Thermosphere: The thermosphere is the outermost layer of the atmosphere, extending upward beyond 100 kilometers (62 miles) above the Earth's surface. In this layer, the temperature increases significantly with altitude due to the absorption of high-energy solar radiation. Despite the high temperatures, the thermosphere would feel extremely cold to humans due to its extremely low density.

These layers are determined based on the vertical distribution of temperature, which changes due to the varying absorption of solar energy and the Earth's radiative balance. Atmospheric composition, circulation patterns, and other factors also contribute to the division of the atmosphere into these distinct layers.