system
Given the following post, respond as if you're commenting on Reddit:
human
Since mountains are changing elevation due to plate tectonics is it possible to know what the highest mountain to ever have existed was?

For example the Appalachians are older then the Rockies and I've been told that at some point in history they were taller. Is it possible that the tallest mountain on earth was at one time in that mountain chain and if so is it possible for us to know what they highest peak ever was?
gpt
I don't see how you could possibly figure out when and where the tallest individual peak in Earth's history was, but you CAN calculate a rough estimate for what the tallest *possible* peak is, based on the structural properties of rock, and the buoyancy of the continental plates.

Build a local mountain too high and it collapses under its own weight. Build a whole continent too high and it sinks into the mantle. The end result no matter how you figure it is that you can't have a mountain on Earth taller than, very roughly, 10 km.

Mt. Everest is 8.8 km. So the tallest mountain ever was probably only marginally taller than Everest, and in fact it's possible (though unlikely, considering all mountain ranges there have been) that Everest IS the tallest ever.