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0 pointsSpare_account4y ago0 comments

Rocks formed on earth have been dated as old as 4 billion years

https://en.m.wikipedia.org/wiki/Oldest_dated_rocks

It is unusual, though, you're right.

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3 comments · 1 top-level

Is it unusual because of weather systems or because of plate tectonics (rocks get pushed into the mantle and melted down and new ones emerge later)?

dredmorbius4y ago

Both, though plate tectonics are the ultimate limit. There's extraordinarily little primaeval crust extant on Earth. The Canadian Shield / Laurentine Plain is one of the largest, and is dated to 3.96 billion years, though the oldest is in Australia (Jack Hills region), with dates to 4.39 billion years via zircon crystals. (I believe that may geologically related to a region in southern Africa, with which it was originally joined, though cannot find a reference.)

The ocean floor is virtually completely newer material, little of it over a 200 million years old (about 5% of Earth's total age), due to subduction. Continental crust is lighter, floats on top of the heavier oceanic crust, and has at least a chance of survival.

https://www.thoughtco.com/how-old-is-the-ocean-floor-3960755

https://en.wikipedia.org/wiki/Canadian_Shield

https://en.wikipedia.org/wiki/Jack_Hills

https://www.geologyin.com/2015/11/44-billion-year-old-zircon...

https://www.geologyin.com/2016/03/the-oldest-mountain-on-ear...

dredmorbius4y ago

The oldest seafloor happens to be that of the Mediterranean, dating to about 280 million years ago. Again, that's trifling compared to the oldest land formations. The Medeterranian is all that remains of the Tethys Ocean.

https://www.thoughtco.com/how-old-is-the-ocean-floor-3960755

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