Layers of crust from millions of years ago are in layers below the outermost crust, which would make sense if the earth was constantly growing in mass and size. Like in millions of years we will fossilize and structures will be buried but unless things just sink into the ground or there is mass added how do older layers of crust get underground?
In: 7
The solid rock that forms the crust and the continents FLOATS on the more dense liquid rock that makes up the [inside of the Earth](https://www.sciencealert.com/images/2021-03/processed/EarthsInnermostInnerLauer_1024.jpg).
So two things happen:
* Volcanoes spew out molten rock which then solidifies and becomes islands or mountains, basically adding to the crust. Over millions of years the wind and the sea erode these mountains, and the resulting sand and dust are transported to the bottom of seas and lakes, and to valleys and plains.
* At the [edges of the continents](https://qph.fs.quoracdn.net/main-qimg-1f2a192aebc28f0419ae40fbc41b354a), there are [subduction zones](https://epl.carnegiescience.edu/sites/dtm/files/subduction%20volcanoes_whiteback.png) where the “extra” crust is pushed down into the molten magma layer and “re-melted” basically.
So basically volcanic ridges under the oceans push out the molten magma, which solidifies and pushes sideways on the crust plates, and this pressure causes the other side of the plates to sink under and re-melt. The crust doesn’t grow upward, it just moves sideways and gets re-melted and recycled, over millions and millions of years.
[Here’s how the continents moved](https://www.youtube.com/watch?v=QhldiOaFqpE) in the past. The ocean-covered “spaces” between the continents is crust that was formed from molten magma and “pushed under” when it hit the continental plates.
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