Space/Science — HabitableZone

Space/Science » in reply to Something I don't quite understand

re: olivine in earth is from recent eruptions
dtb — (archived)

On Earth, new olivine-bearing rocks are being erupted out on the the surface all the time. The olivine that you find exposed -- there's a whole beach loaded with it in Hawaii! --is all "recent" in the sense of thousands or tens of thousands of years old. Not millions or billions.

Since it seems pretty conclusive that there hasn't been a lot of volcanic activty on Mars recently, any olivine-bearing rocks have been exposed for a long time. Given the craters, the surface at Gusev is very old, for example. Likewise, the olivine-bearing layers exposed in Valles Marineris must be old, and should have been weathered if there was a long-ago wet period, or water coursing down and ponding in the canyons.

I'm less clear on how quickly olivine wears away when not exposed to the elements. If you have some intrusive basalt that is deep underground for millions of years on Earth, will there still be olivine present in it?

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