Im so sorry if i sound irredeemably dumb.
I remember learning about strata in high school sciences. The way I understand it is basically our crust and upper mantle are an autobiography of the history of earth. What’s happening now is at the top layer, and what happened way way way super long ago is at the base.
Soooo…. How exactly does this work? What happens to the fossils/etc when they get to the bottom? And how do we keep adding new layers? Obviously the earth isn’t perpetually growing.
Do they just get consumed by the core and regurgitated back into the planet somehow? If so, what happens to things like plastics, non degradeables, and radioactive material when they get there? Is there a limit on how far back we can carbon date? Sorry I tried to google😭😭
In: Planetary Science
Oceanic crust (mostly) gets carried into the mantle as it cools and get dense. As it sinks it heats up again and separates out into different materials.. So some volcanos are actually belching out recycled ocean crust. Continental crust does appear to have grown in volume over earth history, so in general you can think of it as land as starting with volcanos laying down successive layers of material.
The wildcard with stratigraphy is that a.) plate tectonics can result in folding the crust in ways that can put older crust on top of younger crust .b) Erosion can start by turning younger crust into sediment and then cover it over with sediments formed from older crust. c.) Glaciers can move rocks around. This means that, for example, if you look at certain measures of when rock was first formed (zircons) you can find older “detrital” zircons in sedimentary rock mixed with younger ones.
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