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StrangeTangerine1525 t1_iwzyqri wrote

Reply to comment by famished_armrest in Mars was once covered by 300-meter deep oceans, study shows by magenta_placenta

In simple terms, Mars is a significantly smaller planet than Earth is, with around 10% the mass of Earth. This means that gas escapes much more readily from the planet, outgassing from volcanoes is lower because of a colder interior, asteroids do more damage to the atmosphere etc. Much of the water probably escaped during the first billion years of Mars's existence, when the Sun was far more active than it is today, and the planet was regularly bombarded by solar flares. Water high in the atmosphere would be broken apart by UV rays and its constituents would then be lost to space. Some water condensed into polar ice caps and subsurface reservoirs of ice. Even more water likely seeped into the crust and got chemically bound into rocks. It's a complex answer to a simple question. Scientists even today still don't know exactly were all the water left, but the three primary culprits are loss to space, loss to the deep crust of Mars, and then just freezing in the form of ice near the surface, which includes the water we can readily see on Mars today.

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famished_armrest t1_ix01777 wrote

Maybe a complex answer but you did a great job explaining it, thanks for breaking it down for me. I didn't know elements could be lost to space, that's interesting. That doesn't happen on earth right? Naturally I mean.. I thought I remembered reading in a book that the amount of matter on earth and our atmosphere never changes, basically the whole death brings life thing etc. I could be remembering wrong though.

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StrangeTangerine1525 t1_ix0awka wrote

It does, but because Earth is larger planet, and has active recycling processes such as plate tectonics that Mars does not currently have. So while we do lose different gases to space throughout time it is replenished. Though fast forward a billion years from now, when the Sun emits roughly 10% more energy, the Earth will be hot enough that water will be able to rise from the surface directly to the upper atmosphere, and the process that dried out both Mars and Venus will begin. But that's in a billion years so we have nothing to worry about, at least on that front.

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famished_armrest t1_ix0bn2x wrote

Interesting. I'm sure humanity will be long gone by that point anyways. There's a really great book I read a while back called 'A Brief History of Everything' that really puts stuff like this into perspective and explains it well like you do. I remember it saying that if you looked at the history of the world as one day, humanity has been here for less than a minute, that blew my mind. Along with the fact that 99% of all creatures that have lived on this earth are already extinct. Really puts into perspective how frail and insignificant our existence really is.

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