> And above all, I wonder why Venus and Mars don't have tectonics, but we do. Quibble: They both have tectonics (large-scale crustal processes). And may have

> And above all, I wonder why Venus and Mars don't have tectonics, but we do. Quibble: They both have tectonics (large-scale crustal processes). And may have had plate tectonics in the past. Fwiw, here's a recent survey article on Venus[1] - "Why not now?" appears an open question. I didn't quickly find one for Mars. [1] https://link.springer.com/article/10.1007/s11214-018-0518-1 https://link.springer.com/article/10.1007/s11214-018-0518-1