Though the greenhouse effect is sometimes portrayed as a bad thing, trace amounts of gases like CO2 warm our planet's atmosphere enough to sustain life. Global warming, on the other hand, is a separate process that can be caused by increased amounts of greenhouse gases in the atmosphere.
Though the major components of the atmosphere vary little today, they have changed dramatically over Earth's history, about 4.6 billion years. The early atmosphere was hardly the life-sustaining blanket of air that it is today; most geologists believe that the main constituents then were nitrogen gas and carbon dioxide, but no free oxygen. In fact, there is no evidence for free oxygen in the atmosphere until about 2 billion years ago, when photosynthesizing bacteria evolved and began taking in atmospheric carbon dioxide and releasing oxygen. The amount of oxygen in the atmosphere has risen steadily from 0 percent 2 billion years ago to about 21 percent today. .
LAYERS OF THE ATMOSPHERE.
(Palo, Jerwin).
Without our atmosphere, there would be no life on earth. Two gases make up the bulk of the earth's atmosphere: nitrogen (78%), and oxygen (21%). Argon, carbon dioxide and various trace gases make up the remainder. Scientists divided the atmosphere into four layers according to temperature: troposphere, stratosphere, mesosphere, and thermosphere. The temperature drops as we go up through the troposphere, but it rises as we move through the next layer, the stratosphere. The farther away from earth, the thinner the atmosphere gets.
TROPOSPHERE.
This is the layer of the atmosphere closest to the Earth's surface, extending up to about 8-14.5 km above the Earth's surface. This part of the atmosphere is the densest. It contains 75% of the atmosphere's mass. The troposphere is wider at the equator than at the poles. Temperature and pressure drops as you go higher up the troposphere. The tropopause and the troposphere are known as the lower atmosphere.
