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In the formative years of the Earth, the planet was covered in a blanket of magma that gave rise to an incredibly toxic atmosphere. Scientists believe that our home planet at the time was more like Venus, which has a toxic atmosphere where temperatures exceed 400 degrees Celsius. A new study that examined the history of our planet and the process it went through to become the refuge it is for life today.
When rocky planets, such as Earth, begin to form, they go through a process called “accretion”.
This is where the small particles begin to clump together and eventually accumulate to the point where their gravity is strong enough to attract larger lumps.
These small bodies are known as “planetesimals” and are similar to asteroids.
As they grow further, they become “planetary embryos”.
During the latter stages of accretion, while attracting larger bodies, huge rocks hit the first planets, releasing enormous amounts of energy.
The latest accretion impact occurred when a body the size of Mars crashed into Earth, causing much of the first planet to melt.
This melting left the Earth in a blanket of “magma ocean” that would release gaseous hydrogen, carbon, oxygen and nitrogen to form Earth’s first atmosphere.
According to the new study, this first atmosphere would have been rich in hydrogen gas (H₂), ammonia (NH₃) and carbon monoxide (CO).
READ MORE: Venus life: the discovery of phosphine could be very broad: study
“This would have left an atmosphere with 97% CO₂ and 3% N₂, at a total pressure of about 70 times today’s atmospheric pressure. Talk about a greenhouse effect!”
The team then wanted to understand how the Earth cooled down, while Venus, which went through a similar process when it formed, stayed hot.
The answer, according to the study published in the journal Science Advances, boils down to a question of distance.
Mr. Burnham continued: “This relationship between CO₂ and N₂ is strikingly similar to the current atmosphere on Venus.
“So why did Venus, but not Earth, keep the hellishly hot and toxic environment we observe today?
“The answer is that Venus was too close to the Sun. It simply never cooled enough to form oceans of water.
“Instead, the H₂O in the atmosphere remained as water vapor and was slowly but surely dispersed into space.
“On the early Earth, oceans of water instead slowly but steadily absorbed CO₂ from the atmosphere by reaction with the rock.
“So, although both planets started almost identically, it’s their different distances from the Sun that put them on divergent paths.
“The Earth has become more conducive to life while Venus has become increasingly inhospitable.”
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