Eli5 Where does the dirt come from?

Question

When looking at a geological timescale, typically ‘the deeper you dig, the older stuff gets’, right?
So, where does this buildup of new sediment come from?
I understand we’re talking about very large timeframes here, but I still dont really get it.

In: 19

Answer 1

The new dirt on top of one location came from dirt eroding away from another. The history in the one place gets buried, and the history of the other place gets erased. Whether a location gets buried or eroded can change with time, so some location might not have any dirt from the period of 5000YA-7000YA for example, but when digging the dirt from 7001YA will still be below the dirt from 4999YA.