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Comment by chistev

2 days ago

> Well, our planet has magnetosphere and it also had life for a long time already.

But life needed water as a requirement to arrive, right? So are you saying that there was a little bit of water for life to get started, before that same life caused the oxygenation event to create more water over millions of years?

Please explain, thank you.

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chistev

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userulluipeste  1 day ago

Well, yes -- some amount of water must have been in there from very beginning, plus what may have fallen in as icy bodies from outer space afterwards, this much is mentioned in the article itself. The question was not if there was water, but how much of it. Most of today's planetary body of water resides in deep depressions -- seas and oceans, which is very different to what must have been initially. Back then, the surface supposedly had very little relief, due to Earth's crust being much thinner at that time. That meant that, whatever water was there, it must have been shallow, spread to very large areas.¹ This condition was especially propitious for life, as it provided ample space for life to proliferate. The first organisms must have been at the bottom of this large, never drying shallow "ocean" or mesh of (at least often) connected seas. Deep enough to shield the emerging life from UV light, but shallow enough for light to reach the developing life, including the first unicellular algae. Even today, most of life lives on the shallow waters, where plants could find minerals and underwater sunlight, and thus the whole food chain above them could be sustained.

¹ Today's amount of water spread all over an Earth with no relief gives you a kilometers-depth ocean. Even with only some modest amount of relief (as it should have been at the beginning), if it didn't reached the water surface to produce shallow waters, then that's a non-starter for life. The life should have waited a lot of time for the Earth to cool down, for the crust get ticker and thus for a more prominent relief to appear in order for it to finally get any chance to emerge. Therefore, it was very important for life to encounter an environment with just modest amount of water.