Just above the Earth's surface, the atmosphere is a layer of gases fundamental to the existence of life on the planet. After all, it contains the air that all living things breathe. Furthermore, this is where climate phenomena and processes such as the greenhouse effect occur.
- It looks like Earth will run out of oxygen faster than we thought
- Early Earth's atmosphere may have been as toxic as Venus's is today
The atmosphere is made up of 5 layers:
- Troposphere
- Stratosphere
- mesosphere
- thermosphere
- exosphere
But this gaseous layer was not always the same. FreeGameGuide tells how it emerged and transformed until it became what it is today. Next, you will learn what the layers of the atmosphere are and their characteristics.
Formation and evolution of the atmosphere
Earth's atmosphere has changed a lot since the planet formed about 4.5 billion years ago. Planets form from the slow accumulation of gases and dust in the cloud orbiting a young star, and the initial composition of Earth's atmosphere is closely linked to the process of planet formation itself.
As a planet forms, the gases it can trap to form its atmosphere depend on its gravitational pull and the speed at which those gases move. Earth's first atmosphere was probably composed mainly of hydrogen, the main gas present in the solar nebula, as well as methane, ammonia and water vapor. But because hydrogen molecules move at a very high speed, they soon leave Earth's atmosphere. Heavier molecules, which suffer greater gravitational attraction, cannot escape.
Over the next millions of years, as the planet's surface cooled, a period of intense volcanic activity began. The gases released by volcanism became part of the atmosphere. At this time, nitrogen and carbon dioxide become abundant. Also during this period, water vapor begins to condense and accumulate on the surface in liquid form.
When oxygen arrives
The oxygen we breathe today took a few billion years to significantly appear in the atmosphere. It was from primitive forms of life, which did not need this gas to survive, that it began to be released.
About 5% of the atmosphere was oxygen about 600 million years ago and its presence now allows new life forms to emerge. This accumulation continues to a maximum of about 35% of this gas in Earth's atmosphere 300 million years ago. Over the next 10 million years, this value drops again until it stabilizes around 21% — which is still present today.
In addition to oxygen, the atmosphere also contains about 78% of nitrogen. The rest of its composition includes gases such as argon, carbon dioxide, among many others in much smaller quantities.
Knowing the history and composition of the atmosphere, it's time to learn about its different layers.
The layers of the atmosphere
Scientists divide the atmosphere into five layers, according to temperature variation with altitude. Another variable is the concentration of gases, which decreases as we move away from the surface: about 90% of the total mass of the atmosphere is below 16 kilometers.
Troposphere
The layer closest to the ground is the troposphere, where living beings breathe and where phenomena related to meteorological climate occur, such as rain, wind and hail. Temperature decreases linearly with increasing altitude in this layer, which extends to about 17 kilometers above the ground.
Stratosphere
The second is where the ozone layer is located, responsible for preventing the Sun's most dangerous ultraviolet rays from entering. Due to the presence of this element, the temperature profile in the stratosphere is the opposite of the troposphere: it increases as you go up. This layer reaches an altitude of 50 kilometers and is where jet planes fly.
mesosphere
The mesosphere once again shows a decrease in temperature and its upper limit, around 80 kilometers from the surface, reaches -100 ºC. The air is extremely rarefied, but the molecules present are responsible for preventing meteorites from reaching the Earth's surface. Their friction with the air in the mesosphere causes them to disintegrate even in this layer.
thermosphere
Above 80 kilometers is the thermosphere. In this layer, temperatures rise rapidly, reaching around 1,500 °C. There is a large concentration of ions from solar activity and it is in this layer that auroras occur. Its length is variable, reaching an altitude of 800 kilometers during periods when the Sun is very active. The International Space Station is also in the thermosphere, about 400 kilometers above the Earth's surface.
exosphere
The last layer of the atmosphere, the exosphere, has no defined upper limit. It is mainly composed of hydrogen and helium in very low concentrations and, together with the thermosphere, forms the so-called ionosphere.
