Are marine fossils in the mountain happens due to lower sea levels? https://9gag.com/gag/aBme0M2
This one says it is

I am not sure whether to ask this in geology or biology.
How does marine fossils show up in mountains?
Leonardo was wrong about this.  It is not due to sea level dropping (except in very isolated cases), it's due to the land rising.  Sedimentary rocks that form in sea beds are often uplifted by tectonic processes to form mountains and plateaus.  See e.g. https://en.wikipedia.org/wiki/Sedimentary_rock