The Earth’s atmosphere is massive, extending so far that it impacts the International Space Station’s path. But how did this gigantic gaseous envelope come to be?

That is, what is the purpose of Earth’s atmosphere?

In a nutshell, gravity is the reason our atmosphere exists. Earth was a molten planet with no atmosphere when it originated roughly 4.5 billion years ago. According to the Smithsonian Environmental Research Center, the atmosphere is created when the planet cooled, mostly from gases erupted out of volcanoes (SERC). According to SERC, this ancient environment was substantially different from today’s, with hydrogen sulfide, methane, and 10 to 200 times as much carbon dioxide as the present atmosphere.

“We think the Earth began with an atmosphere similar to [that of] Venus, with nitrogen, carbon dioxide, and maybe methane,” said Jeremy Frey, a physical chemistry professor at Southampton University in the United Kingdom. “Life must have started someplace, very probably at the bottom of an ocean.”

The photosynthetic mechanism originated some 3 billion years ago, allowing single-celled creatures to harness the sun’s energy to convert carbon dioxide and water molecules into sugar and oxygen gas. According to Frey, this resulted in a significant rise in oxygen levels. “And it is the largest pollution event, you could say, that life has ever done to anything,” he continued, explaining how the Earth was gradually changed.

According to Frey, the Earth’s atmosphere now contains around 80% nitrogen and 20% oxygen. According to the National Center for Atmospheric Research, the atmosphere also contains argon, carbon dioxide, water vapour, and a variety of other gases (NCAR).

Fortunately, these gases are present. Our atmosphere acts like a comforter around the Earth, shielding it from the sun’s harsh rays and reducing temperature extremes. According to the NCAR, the greenhouse effect occurs when energy from the sun reaches Earth and is absorbed and released by greenhouse gases in the atmosphere. There are various forms of greenhouse gases, with carbon dioxide, water vapour, methane, and nitrous oxide being the most common. The temperature of the Earth would be below freezing if the greenhouse effect did not exist.

Today, however, greenhouse gases are uncontrollable. According to NCAR, the greenhouse effect increases as people emit more carbon dioxide into the atmosphere. As a result, the planet’s climate warms.

Surprisingly, no other planet in the cosmos has a similar atmosphere to Earth. Although Mars and Venus have atmospheres, they cannot host life (at least not Earth-like life) due to a lack of oxygen. Indeed, the atmosphere of Venus is mostly carbon dioxide with sulfuric acid clouds, and the ‘air’ is so dense and hot that no person can breathe there. According to NASA, Venus’ thick carbon dioxide atmosphere traps heat in a runaway greenhouse effect, making it the hottest planet in our solar system. The temperature on the surface is hot enough to melt lead.

“The fact that Earth has an atmosphere is exceedingly rare among the planets in the solar system, in that it is unlike any other planet,” Frey said. The pressure on Venus, for example, is around 90 atmospheres, which is the same as plunging 3,000 feet (914 meters) into the ocean on Earth. “The first Russian spacecraft that traveled there [to Venus] only recorded for a few seconds before being smashed,” Frey said. “No one really realized how hot it was.”

So, the atmosphere of the Earth is life, and life as we know it would not exist without it. “For life to begin on Earth, the appropriate environment was required,” Frey added. “It has generated that environment, as well as the conditions for living in that atmosphere. The biological system is completely dependent on the atmosphere.”

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