Once upon a time, this blooming sphere was that our house is an inhospitable ball of molten lava. A catastrophic collision about 4.5 billion years ago blew what the existing atmosphere early earth had in space, formed our moon and for a while melted our entire planet.
How our current atmosphere was then so different from ours in the solar system has been a continuing mystery. Some have speculated that this was due to the Earth having a distinct initial composition, perhaps because some parts of the inner planetary embryos came from the outer regions of the solar system. Others suspect the subsequent evolution of the earth allowed it to form an atmosphere that could give birth to life.
Now, scientists have used chemical reactions recorded in ancient rocks and levitating lava balls in the lab to work out the first incarnation of our atmosphere.
Our planetary neighbors have both carbon dioxide (CO2) rich atmospheres with a sprinkling of nitrogen (N2), which is very different from the current nitrogen oxygen (N2-O2) dominated air of the 4.54 billion years, despite all the inner planets that form in the same way.
A team of researchers led by ETH Zurich geochemist Paolo Sossi made balls of molten lava – mini early earths – in the lab from ordinary mantle stone called peridotite. They float these lava spheres in different streams of chemical gases of which the atmosphere of the earth once existed.
“Four-and-a-half billion years ago, the magma – the molten rock that now lies beneath the earth’s crust – constantly exchanged gases with the overlying atmosphere,” Sossi explained. “The air and the magma have influenced each other. That, you can learn about one from the other.”
After the team laser heated the mini-Earths in their streams of various ‘atmospheric’ gases until the molten lava reached almost 2,000 ° C (3,632 ° F), they cooled rapidly. The resulting glass balls of marble size captured a record of the ‘atmosphere’ in which they were, just as the mantle of the earth would have long ago.
Iron binds differently to oxygen depending on the concentration of its exposure. If there is not much oxygen, it will bind one iron atom to one oxygen atom, but if there is enough oxygen, it will bind in a 2: 3 ratio. Comparing their experiments with real rock samples formed on early Earth, Sossi and colleagues concluded that the oceans of the molten earth exhale the early atmosphere of CO2 and N2 of our planet.
“If you produced an atmosphere from magma in the right oxidation state, you get one that consists of about 97 percent carbon dioxide and 3 percent nitrogen when it cools down, the same ratio found today on Venus and Mars,” he explained. Sossi.
Life-forming amino acids would not form very easily in this combination of atmospheric chemicals.
But then, unlike its neighboring planets, the earth became a water world.
The water of Venus was probably almost completely lost during its early evolution, due to its proximity to the Sun, and the water of Mars was probably trapped in ice caps before the planet was 3.8 billion years old because it was too far away.
“The prolonged presence of surface water on Earth is the key to the further development of its atmosphere,” the team wrote in their paper.
They suspect that this ocean of salt water slurps the CO2 out of the atmosphere, allowing our planet’s plate tectonics to digest it and deposit it in the earth’s crust and mantle. The mass of the earth and perfect position of the sun allowed our planet to retain water fast enough long enough to change the entire atmosphere. This began the relatively stormy relationship of the earth with an oxygen atmosphere that paved the way for life.
Her research was published in Science Advances,