Earth might have become habitable sooner than thought. But for that to happen, something had to remove all those GHGs more quickly.
protoplanetary disk
Before Earth could cool, it had to scrub a lot of carbon from its atmosphere. But scientists have found it challenging to piece together events on the very young Earth. For one thing, the geological evidence is scant. The Hadean was not only enigmatic but dynamic. The planet underwent a lot of changes during those 600 million years. But geological evidence shows that Earth’s surface environment was similar to present-day Earth’s by the middle of the Hadean. “Under what conditions a harsh surface environment could turn into a habitable one remains uncertain,” the authors write in their paper.
But the question is about the time involved. If the climate was moderate and similar to modern Earth’s 4 billion years ago, the carbon sequestration had to be very efficient. How did it all work? But that’s only part of the explanation for the the geologically rapid transformation of Earth’s atmosphere during the Hadean. Magnesium-rich minerals may have been plentiful, but something else needed to happen. Remember that the build-up of carbon in the atmosphere stemmed from the cooling of the magma ocean. As it cooled and solidified it released huge quantities of GHGs into the atmosphere.
heterogeneous structure,” the authors write in their paper. “We propose that rapid recycling is possible with a chemically heterogeneous mantle…” The model the authors developed also accounts for ocean formation. A heterogeneous mantle has more convection, which exposes more magnesium-rich rocks to the atmosphere. That’s what removes GHGs from the atmosphere, cooling to to more modern day temperatures. But the more rapid convection in the mantle also releases more volatiles into the atmosphere. The amount of volatiles released “… exceeds a threshold of 0.
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