Mars is a cold desert planet with a thin, dry carbon-dioxide atmosphere.

The geology of Mars, however, shows signs of an active past, with

hot-spot volcanism, and tantalizing signs of ancient water flows. While

a cold, dead desert planet today, Mars' past may have been warmer and

wetter, with liquid water during the first third of its history. This

lecture reviews the properties of Mars, and describes the evidence for

its active past. Recorded 2007 Nov 9 in 1000 McPherson Lab on the

Columbus campus of The Ohio State University.