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A Brief History of Time

In order to determine the sequence in which events occur on a planetary surface, scientists study the relationships between surface features. In this image, there are two major relationships that help us understand how this landscape formed. The crater to the right (interior is shadowed) is sitting on top of the larger, filled crater that takes up most of the scene. Because it sits on top, it must be younger. Scientists call this the Law of Superposition. If we look at the large, filled crater itself, we see that it has been altered by the formation of a scarp. Because the scarp altered the basin, the scarp must also be younger. This is called the Law of Cross-cutting Relationships.

Date acquired: August 29, 2012

Image Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington