4 ms·
I agree with this comment fully but I just wanted add a little on the subduction. It’s a lot quicker than people think. The vast majority of rocks we can find
by jamiek88 2y ago
I agree with this comment fully but I just wanted add a little on the subduction.
It’s a lot quicker than people think.
The vast majority of rocks we can find that aren’t of extra terrestrial origin are only around 200 million years old.
>A few seams of very old rock have been discovered, such as the billions of years old Nuvvuagittuq greenstone belt in Hudson Bay, Canada, as well as similarly ancient outcrops in Australia, China, Greenland and South Africa. But even this very old rock has had a complex history. “Exposure to high temperatures during past collision can change the chemistry,” notes Boyet. “This disturbs the isotopic system we use for dating rock.”
https://cordis.europa.eu/article/id/442712-are-all-rocks-on-earth-the-same-age https://cordis.europa.eu/article/id/442712-are-all-rocks-on-...
- jjk166 2y agoMost continental crust is over 2.5 billion years old. Very old rocks aren't exposed at the surface very frequently, because they tend to get covered over in younger rock, but it's still there, and we can sample it with deep drilling. Oceanic crust tends to be less than 200 million years old, though even then there are some much older examples.