I believe that was my post. I decided to resuscribe for a while.
The reference is Barrow and Tipler (the mad hatter), The Anthropic
Cosmological Principle, pp 307-309.
The reason Mars has a higher mountain is that the gravitational field on
Mars is less than Earth's. The theoretical maximum height of a Martian
mountain is, according to Barrow and the "Hatter" 8.8 x 10^-3 of the
planetary radius. This yields a theoretical height of 59 km. Olympus
mons is 25 km high.
I knowmof no theoretical limit to a trenches depth which has been
calculated. But there must be one. Pressure would tend to try to force
the trench closed.
Foundation,Fall and Flood