Those of you who read my weblog may already have read this entry, but Elizabeth suggested that it might be a nice topic for discussion here at the Salon. So if you care to geek out about science/geology, comment away! (I’ve added some additional comments below it.)

The question of whether granite might exist on the Martian surface recently came up independently two days in a row, in completely unrelated conversations with people who can’t possibly be in collusion. This was inspiration enough for me to do some googling, and sure enough, it seems that granite has indeed been detected on Mars (several years ago, no less). Why would this be surprising? Because on Earth, at least, a lot of granite forms as a result of plate tectonics (leading to subduction, melting, and crystallization of magma under the surface, which yields granite), and Mars hasn’t shown any persuasive evidence of tectonic activity ever existing. While it seems plausible (to this humble annalist) that magma inside a volcanic chamber could fail to erupt and manage to cool and crystallize, leading to granite in subterranean chambers, it’s less clear how you’d subsequently get it up to the surface, especially without plate tectonics. But note that the granite identified in the above link occurs in a crater, not a volcanic caldera; the theory seems to be that the crater-forming impact exhumed down to where the granite was. Very interesting.

Now if only they could find the darn carbonates!

In other Mars-related news, the Spirit Rover recently found what they believe to be a meteorite on the surface of Mars. They’re calling it “Allan Hills”, which appears to be at least partly coincidence rather than irony (though most meteorites are made from nickel + iron!). Allan Hills, on Earth, is a location in Antarctica where several meteroites have been found, and the trend at the moment for naming features on Mars is to honor Antarctic research stations. But as you may know, Allan Hills is also the source of the hugely controversial ALH84001 meteorite, which most people agree comes from Mars and some people believe contains evidence of past (Martian) microbial life. It’d be pretty cool if the Martian Allan Hills meteorite became the subject of a controversy over Earth microbial transport… but due to various physics constraints, a meteroite on Mars is more likely to have come from the asteroid belt (further out from the Sun) than from the Earth.