Lava flows in a maria

Lava flows in a maria

. Lunar volcanism is seen frozen into place on the Sea of Serenity in this Apollo 17 image taken in December 1972. Crater Condorcet (top) and Crater Bessel (bottom) are superposed on the lava, but the lunar maria contain relatively few craters when compared with the lunar highlands. The maria formed a secondary crust on the Moon, when lava filled the giant impact basins over a period of several hundred million years ending around 3.15 billion years ago. The fluid spread rapidly, creating thin extensive sheets rather than piling up to form volcanoes. (Courtesy of NASA.)

Copyright 2010, Professor Kenneth R. Lang, Tufts University