Which is the lowest layer of the Earth's atmosphere, where almost all weather phenomena occur?

The troposphere is the lowest layer of the Earth's atmosphere, beginning at the Earth's surface. It contains about three-quarters of the mass of the atmosphere and almost all of its water vapour, dust and clouds, so nearly all weather phenomena, such as clouds, rain, snow, storms and winds, occur in this layer.

The height of the troposphere varies: it is about 18 km at the equator and about 8 km at the poles, because warm air at the equator rises higher. In the troposphere, temperature decreases with height at an average rate of about 6.5°C per kilometre, called the normal lapse rate. The boundary at the top of the troposphere is called the tropopause. The greenhouse effect also takes place mainly in this layer.

The layers of the atmosphere, from the bottom up, are:

Troposphere: weather, clouds; temperature falls with height.

Stratosphere: from the tropopause to about 50 km. It contains the ozone layer (mainly between 15 and 35 km), which absorbs harmful ultraviolet rays from the Sun. Temperature rises with height. The air is calm, so jet aircraft fly in the lower stratosphere.

Mesosphere: from about 50 to 80-85 km. It is the coldest layer, and meteors burn up here.

Thermosphere: from about 80 km to several hundred km. Temperature rises sharply. It contains the ionosphere, which reflects radio waves back to the Earth, and the auroras occur here.

Exosphere: the outermost layer, where the atmosphere gradually merges into space.

The atmosphere is made up mainly of nitrogen (about 78%) and oxygen (about 21%), with argon (about 0.93%), carbon dioxide (about 0.04%) and small amounts of other gases.

Why not the other options?

• ✗Stratosphere is the second layer, which contains the ozone layer.
• ✗Mesosphere is the third and coldest layer, where meteors burn up.
• ✗Thermosphere is the upper layer that contains the ionosphere.