For good reason, Early Earth is often described as Hadean. The primordial eon was characterized by heat trapped beneath a thick blanket of carbon dioxide and water vapor.
The conditions should have been much worse. After just a few hundred million years or so of cooling, our planet was already starting to look very hospitable.
The rapid loss of greenhouse gases would have to be taken into account in order to explain the dramatic transformation of Earth.
The only problem is that the period in our planet's history left few traces of its geology. It would take evidence of the planet's surface conditions with the minerals that would have sunk into the ocean.
Any hypotheses we come up with to solve the mystery of the missing gas have to rely on circumstantial evidence.
Two researchers from Yale University ran the numbers on a speculative scenario in which weird rocks that no longer exist on Earth would soak up all the CO 2. The idea seems to work out.
A massive amount of atmospheric carbon had to be removed according to planetary scientist Yoshinori Miyazaki, who is now working at the California Institute of Technology.
We set out to build a theoretical model for the very early Earth because there is no rock record.
The Hadean eon on Earth is largely explained by astrophysical and geochemical models.
The Earth-Moon system is most likely the result of a collision between two planets, one roughly Mars and the other more or less the mass of Earth today.
A molten lump of swirling minerals and gas that was kept warm by a constant downpour of rubble from space would have come out of that mess.
A long period of heat and chaos might have been caused by a greenhouse atmosphere of carbon dioxide and water. To get a sense of what that might look like, one needs to look at Venus.
There are signs that the Hadean already harbored oceans after a few hundred million years of cooling.
The carbon cycle seems to have kept temperatures stable by the end of the eon around 4 billion years ago.
One possibility is that the carbon in the atmosphere could have dissolved into the oceans, transforming into solid carbonates, which could have sunk and become embedded in the mantle.
It is a nice idea, but it is important to know if the numbers add up.
They pulled together models on fluid mechanics, heat movement, and atmospheric physics to see if they could make the hypothesis work.
If a certain type of rock was exposed on our planet, the results suggest it could be.
The rocks would have been enriched in a mineral called pyroxene, and they would have had a dark greenish color.
They were enriched in magnesium and had a concentration level that was not seen in present-day rocks.
A stabilizing process that would take millions of years instead of billions of years could be achieved with a rapidly churned crust of wet, molten rock.
After a cooling that gave us a regenerating crust consisting of a few slowly moving plates, all of that magnesium-rich rock would be left far beneath our feet.
As the crust turned over, water-logged minerals would have quickly dried up, filling the oceans to levels we see today.
The scenario is intriguing because it would have helped kick-start life in other ways.
As an added bonus, these weird rocks on the early Earth would react with the water to create a large amount of hydrogen, which is widely believed to be essential for the creation of biomolecules.
It is a kind of science that is begging for hard evidence, which is buried both deep in time and under the surface.
Earth'shellish period will keep its mysteries a little longer. We are coming to an understanding of why our planet became a paradise.
The research was published in Nature.
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