When we learn about history we learn that layers at the bottom are older and stuff up top is newer, so it’s like things just keep piling up. Where did we get the stuff then? Will we run out of stuff?
In: Geology
There’s a lot of stuff and it keeps getting recycled.
The continental plates are being pushed together in some places and one might get pushed underneath another one. The one that gets pushed underneath gets melted back into the mantle (basically lava). In other places the plates are being pushed apart or sliding against each other and new rocks are created where lava solidifies.
So rocks become lava and lava becomes rocks.
Rocks get pushed up high into mountains and water and wind erodes them away and they get carried with wind and water down to the sea where they create layers of sediment. Those layers either get lifted up over time or get further buried and melt back into lava.
And all of this keeps happening all of the time over and over and over again.
There is just a lot of it so sometimes the same bits of rock get metamorphosed and eroded sedimented and eroded and metamorphosed over and over and over again while other rocks might get more completely destroyed and melted back into the earth’s mantle.
The earth is very big even compared with the biggest mountains – so the bits that get built into mountains or eroded away into sediment don’t really mean a lot compared with the huge volume of crust there is on earth (it’s thinner under the ocean, but it covers the whole earth).
So while we have lost a LOT of geological history that can never be recovered because it’s all been melted (basically)… there is SO much crust and it doesn’t all get recycled at anything like an even rate so there are plenty of really really old layers of rocks as well as much “newer” rocks being built all the time from undersea volcanoes.
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