What Happened When?

Studying what happened when tells geologists about the history of Mars. A crater that punched through the surface of Mars reveals multiple layers formed previously below the surface. Half of the crater was then destroyed by the opening of the channel. Small craters pepper the ejecta blanket of the larger crater but a few are visible in the channel, another clue to its younger age. The most recent signs of activity are the boulders that have tumbled down the sides of the channel. https://photojournal.jpl.nasa.gov/catalog/PIA25447