Huh? The "last couple of hundred million years" involves all current above sea-level landmass being subducted back into the mantle - probably more than once. We

Huh? The "last couple of hundred million years" involves all current above sea-level landmass being subducted back into the mantle - probably more than once. We're talking about the Himalayas rising up and going back into the magma of the Earth's mantle and rising up again. I am really curious what kind of sign you envision will survive that onslaught.