How Earth acquired its three atmospheres

We know that our own climate can change, but we tend to assume that the atmosphere itself has always been the same as it is today, composed almost

How oxygen accumulated

entirely of nitrogen (78 percent) and oxygen (21 percent). That is wrong. Our present atmosphere is the third atmosphere the Earth has possessed.

The first atmosphere is the one that cloaked the planet while it was forming, around 4.5 billion years ago. At that time rocks were continually smashing into the surface, and each time this happened the impact generated enough heat to vaporize some of the ingredients. The resulting gases formed the atmosphere. Most space rocks contain some water, and comets contain so much they are sometimes called "dirty snowballs." Consequently, the first atmosphere was mostly water vapor, with small amounts of hydrogen, nitrogen, carbon monoxide, and carbon dioxide. Heat from the repeated impacts—like the heat that warms a nail after prolonged hammering—meant the atmosphere was much too hot for water to exist as a liquid. The water vapor remained a gas, and there were no clouds.

Then the Earth was involved in a major collision with a body about the size of Mars. This smashed both bodies and as gravity drew the fragments together again, they assembled themselves not as one body, but as two: Earth had acquired its Moon. The atmosphere also returned, but by now the Earth was sufficiently massive, and its interior was hot enough, for volcanoes to begin erupting. There were many more active volcanoes than there are now and the gases they released became part of the atmosphere.

As more and more rocks hit the Earth, Moon, Venus, and Mars and became part of them, the number of rocks orbiting the Sun decreased, and so the bombardment eased. This allowed the Earth to cool. After a time it had cooled sufficiently for water vapor to start condensing. Clouds formed and it began to rain. Almost all of the atmospheric water fell to the surface, where it filled the low-lying areas to form vast oceans. At the same time, the atmosphere also lost its hydrogen. Earth's gravity was insufficient to retain this lightest of all gases and little by little it drifted away into space. The atmosphere then probably consisted of about 95 percent carbon dioxide and 3 percent nitrogen, with small amounts of carbon monoxide and other gases. This was much like the atmospheres of Venus and Mars, and it was much denser than our present atmosphere. The surface air pressure was probably around 365 lb. in.-2 (2,500 MPa, 25 bar).

Carbon dioxide then reacted with water and with calcium and magnesium in the surface rocks to form carbonates. These accumulated in the oceans, where they formed sediments that were slowly compressed and heated until they were transformed into carbonate rocks, such as limestone. After some hundreds of millions of years, this process removed a great deal of carbon dioxide and reduced the surface pressure. This in turn slowed the reactions and the atmosphere stabilized. Earth then had its second atmosphere, still consisting mainly of carbon dioxide.

Renewable Energy 101

Renewable Energy 101

Renewable energy is energy that is generated from sunlight, rain, tides, geothermal heat and wind. These sources are naturally and constantly replenished, which is why they are deemed as renewable. The usage of renewable energy sources is very important when considering the sustainability of the existing energy usage of the world. While there is currently an abundance of non-renewable energy sources, such as nuclear fuels, these energy sources are depleting. In addition to being a non-renewable supply, the non-renewable energy sources release emissions into the air, which has an adverse effect on the environment.

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