In Mare Frigoris, this creates huge wrinkle ridges. The longest ones are roughly 250 miles (400 kilometers) long, or more than the distance between New York City and Washington, D.C. They also rise about 1,000 feet (333 meters) off the surface.
We can estimate the age of these ridges using "crater counting," or simply adding up the number of craters in a particular region. We know roughly how often objects hit the moon to generate these craters, but tectonic activity can cover them up over time. That means that by comparing the estimated collision rate to the actual number of craters present, scientists can have a rough idea of how old a region is. We also can see signs of craters "aging" — collecting debris from other impacts, for example. The moon might be old, gray, and wrinkled, but it's not dead yet.
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