Earth's Atmosphere

Science: Summary of the Earth's Atmosphere

The atmosphere is the air that is wrapped all around a planet. Not all planets have atmospheres.   In order to have an atmosphere, the planet has to have enough gravity to hold on to light atoms like hydrogen and helium and keep them from floating away into space.   That means that the planet has to have a lot of mass.   Because the force of gravity is stronger near the planet and gets weaker as you get further away, the atmosphere is thicker close to the ground and gradually gets thinner as you go further out into space.   There is no sharp edge to the atmosphere.   It is also a buffer that protects us from meteorites, a screen against deadly radiation, and the reason radio waves can be bounced for long distances around the planet. Composition of the Atmosphere: Present composition of the atmosphere is 79% nitrogen, 20% oxygen, and 1% other gases. Layers of the Atmosphere: Five major layers: The troposphere is the layer that provides our weather.   It contains about four-fifths of the Earth's air, but extends only to a height of about 17 kilometers at the Equator and less at the Poles. What happens within the troposphere: as warm air rises to form clouds, rain falls, and winds stir the lands below.   Typically, the higher you go in the troposphere, the colder it gets. Above the troposphere is the stratosphere.   It extends to a height of 50 kilometers and includes the ozone layer, which blocks much of the sun's harmful ultraviolet rays. The stratosphere is warmer than the troposphere because of the energy from the ultraviolet light absorbed by the ozone.   At its base, the stratosphere is extremely cold.   At its top, the temperature has risen back nearly to freezing. Mesosphere: In this layer, the air temperature drops again at the top.   Meteors generally burn up in the mesosphere, which extends to a height of about 85 kilometers.   This is why the Earth's surface is not pocked with meteor craters, like the moons.   Above the...