The history of the Earth is a very tumultuous one, one that began around 4.5 billion years ago. An essential part to the history of the Earth and the development of life as we know it is the Earth's atmosphere. The atmosphere is the layer of gases that have been held together to the Earth because of its gravtiy. The atmosphere is composed of a variety of gases, like nitrogen, argon, carbon dioxied, oxygen, and many other elements. In order to fully understand the atmosphere, however, we must first understand its history.
The ancient history of the Earth's atmosphere is unknown by scientists. Each of them have speculations about what it was like and what it was composed of. The current atmosphere that we experience today is often called by scientists the third atmosphere, as there were two atmospheres before it that were composed of a variety of different elements. The first atmosphere is the one that was around when the Earth had just formed. It was mainly composed of the elements Hydrogen and Helium. This atmosphere was destroyed quickly by solar wind, the sun, and the constant heat of the Earth's core.
The second atmosphere came about 4.4 billion years ago. By that time, the Earth had cooled down enough to form a crust, and volcanoes littered the landscape. Through these volcanoes, huge amounts of carbon dioxide, water vapor, and some nitrogen. At this point, there was no oxygen in the atmosphere. Later on in the period of the second atmosphere, the carbon dioxide was absorbed.
Then, about 3.3 billion years ago, bacteria came to be, and they started to oxygenate the atmosphere. Then, plants that could photosynthesize evolved. The nitrogen that is in the current atmosphere was created when the oxygen that was released reacted with the chemical ammonia. Finally, the ozone layer formed, which is a layer of O3 that protects organisms from ultraviolet radiation.
The current atmosphere is composed of many layers. Their names are the Troposphere, the Stratosphere, the Mesosphere, the Thermosphere, and the Exosphere.
The Troposphere is the lowest layer of the Earth's atmosphere. It starts at the surface, and can extend upward anywhere from 7 kilometers to 17 kilometers. The tropospere contains about 80% of the mass of the atmosphere. It is where the majority of the weather of the Earth occurs. The boundary between this layer and the next layer of the atmosphere, the Stratosphere, is called the Tropopause.
The Stratosphere contains the layer of the atmosphere known as the ozone layer. This layer contains O3 molecules instead of O2 molecules. This region of the atmosphere extends from the Tropopause to about 51 kilometers. It is where most weather balloons go up to. Interestingly enough, the temperature gets warmer as one ascends through this layer, not colder. The boundary that is between this layer of the atmosphere and the next one, the mesosphere, is called the Stratopause.
The Mesosphere is the middle layer of the atmosphere. It extends from the Stratopause to about 80-85 kilometers high. The temperature gets colder as you ascend through this layer, and at the upper part of the layer, the temperature is a mere -148 degrees Fahrenheit. Most of the meteors that enter the Earth's atmosphere burn up in this layer. The boundary between this layer and the next one, the Thermosphere, is called the Mesopause.
The Thermosphere is the layer of the atmosphere above the Mesosphere. It contains the lower part of the ionosphere, which is the area of the atmosphere that is responsible for auroras. The ISS orbits the Earth in this level, as well as the space shuttle. The temperature increases with height to the top of this layer, which is 640 kilometers. The temperature is really high at the upper layer of this level, but you would not feel it because the density of this layer is really low. The boundary between this layer and the Exosphere, the next layer in the atmosphere, is called the Thermopause.
The Exosphere is the final layer of the Earth's atmosphere. It extends from the Thermopause to about 10,000 kilometers. This layer contains very few particles, and after it is open space.
The Earth's atmosphere is a fascinating place. It is what sustains life on this planet, and it is what makes Earth Earth.