Atmosphere

Atmosphere of Earth

The Earth is an oasis of life, a singularity that is the cocoon of gas that surrounds it.
This layer of air insulates us from space and protects us.
The Earth's atmosphere (from Greek ἀτμός, steam, air and σφαῖρα, sphere), this is miraculous shield coverage of gases surrounding the Earth. Dry air consists of 78.08% nitrogen, 20.95% oxygen, 0.93% argon, 0.038% carbon dioxide and traces of other gases.
The atmosphere protects life on Earth by absorbing ultraviolet solar radiation, warming the surface, trapping heat from the greenhouse effect and reducing the temperature differences between day and night.
There is no clear border between the atmosphere and space, the outer boundary of the atmosphere is defined as the distance where the supposed atmospheric gas molecules continually undergo gravity and the interactions of its magnetic field.
The layer of air varies greatly depending on the latitude and the Earth's magnetic field continually distorted by the solar wind. As seen in this picture, the air becomes less dense and gradually fades into space.
But the altitude of 120 km marks the boundary where atmospheric effects become noticeable during re-entry of an object. The Kármán line lies 100 km, is considered the boundary between the atmosphere and space, but the last molecules of atmospheric gas that constantly undergo gravity are certainly much further. The atmosphere is divided into several layers of varying importance.
Their limits were set according to the discontinuities in the variations of temperature, depending on the altitude as the temperature decreases with altitude.

We live in the troposphere where the air is denser and less cold and the pressure is greatest. In this environment, life has adapted perfectly. The morphology and metabolism of living beings have been shaped by the atmosphere.
Different atmospheric layers of the Earth:
- Troposphere (change in Greek): the thickness of the troposphere varies between 0 and 13 to 16 km at the equator, and between 0 and 7 to 8 km at the poles. It contains 80 to 90% of the total mass of air and almost all of the water vapor. This is the layer of occurrence of the weather phenomena (clouds, rain, heat convection, winds).
- Stratosphere is above the troposphere, the stratospheric layer up to 50 km altitude. This is where lies much of the ozone layer.
- Mesosphere is the layer that lies between 50 km and 80 km altitude where the temperature decreases to -100 ° C.
- Thermosphere is the layer that lies about 80 miles and goes up to 640 km altitude. In this layer the temperature increases with height and reach over 1000 ° C but the pressure is so low that it is not felt.
- Exosphere is the layer that gradually fades into space up to 100 000 km altitude and probably to the moon.

Image: The different layers of the atmosphere, less dense, gradually vanishing into space. This image of Earth's horizon, bright colors, was taken July 29, 2009, the STS-127 crew in orbit around the Earth in the space shuttle Endeavour. Image Credit: NASA

Blue line of the atmosphere

The atmosphere of the Earth is unique, it exists nowhere else, for the International Space Shuttle, it can be seen in the sky like a thin blue line miraculous.
The sublime sun in this picture, the colors of this protective layer of life on Earth.
The Earth's atmosphere is the result of a complex evolution that started there are several billion years. It is the iron dissolved in the oceans, a remnant of the many bombings of meteorites, which has patiently released oxygen into the atmosphere.
The composition of the atmosphere makes it relatively transparent to electromagnetic radiation in the visible spectrum. By cons is relatively opaque to infrared radiation emitted by the ground, causing the greenhouse effect. When light passes through the atmosphere it is scattered in all directions, this phenomenon is called Rayleigh scattering.
This explains the blue color of the atmosphere which is spread more easily wavelengths shorter, so the blue compared to the longer wavelengths like red.
The wavelength of light radiation is increasing from blue to red. The wavelength of blue is approximately between 446 and 520 nm and varies in brightness, cyan tint darker as Prussian blue or midnight blue.

This air is unparalleled, Uranus and Neptune are shrouded in clouds of frigid gas, Mars and Mercury have an extremely tenuous atmosphere, Jupiter and Saturn are only the atmosphere without solid surface, they are gas giants.
One planet has an atmosphere like the Earth in its founding and Venus, our closest neighbor. But the atmospheric pressure of Venus is huge, 90 times higher than on Earth.
This pressure is accompanied by very high temperatures, 480 ° C on average.
This temperature is enough to melt lead on Earth. More thick clouds are composed of concentrated sulfuric acid, which darkens the skies of Venus. While the Earth and Venus are planets binoculars, their atmospheres are very different.
According to David Crisp, a researcher at the Jet Propulsion Laboratory / California Institute of Technology, the giant collision between Earth and a protoplanet the size of Mars, who gave birth to the moon, cleared the land of the primitive atmosphere of CO2 reign even on Venus.

Image: On this beautiful sunset distance, one can see the layers of the atmosphere. This image of the horizon of the Earth, was taken by the crew of STS-129 Space Shuttle International. Image Credit: NASA

Origin of the Earth's atmosphere

To understand the origin of our atmosphere, we must go back to the formation of our solar system, there are 4.5 billion years. The primitive atmosphere of Earth is born in the distant past. The enormous amounts of material sticking together to form protoplanets, Jupiter and Saturn from the Sun, will become gaseous planets. On Earth matter condenses into a hot core. The gases expelled by the molten rock evaporate and form the primitive atmosphere, held by gravity around the globe. The powerful solar winds have the effect of expelling the atmospheric gas nearby planets. The Earth has maintained its atmosphere through the magnetic field generated by its core that prevents the flow of ions and electrons to carry the solar air. This air contains the origin of large quantities of CO2, as on Venus at present (95% CO2), superheated water has evaporated from Venus. According to David Crisp, a researcher at the Jet Propulsion Laboratory / California Institute of Technology, the giant collision between Earth and a protoplanet the size of Mars, who gave birth to the moon, cleared the land of the primitive atmosphere of CO2 reign even on Venus. At this time our atmosphere is no longer composed of rock that steam.

Several million years later it is nitrogen, CO2 and water vapor, elements that come from heaven and earth. Nitrogen and CO2 are discharged from the molten core, volcanic eruptions, the water must have come from comets that collide with our planet that time regularly. Until then, there is still no oxygen or molecular oxygen, the gas we breathe.
The oxygen would have appeared during a sudden change, there are 2.5 billion years. These are the cyanobacteria that have invaded Earth and have rejected enough oxygen to make it a permanent part of the atmosphere. It's that time of the great oxidation. Cyanobacteria have learned to oxygenic photosynthesis, absorb CO2 and use solar energy to crack water molecules, releasing oxygen. The strong oxidizing power of oxygen transforms the iron into iron oxide which is deposited on the seabed. Once saturated minerals, oxygen begins to accumulate in the atmosphere. Under the pressure of oxygen, life will evolve as we know it today.

Image: Stars are formed among nebula of dust and gas.