Researchers studying the data from the Magellan probe had a problem: there weren't enough impact craters.

To help solve this problem, a map of all impact craters on Venus was produced. The distribution was totally random1!

Now, since impact craters happen over time, one would expect there to be relatively more craters in older areas of the planet. This led Gerald Schaber and others to a startling conclusion: the rocks across the entire surface of the planet had to be the same age! This is in stark contrast with the geology of, say, the Earth: Some rocks were formed last week, others billions of years ago.

Given the actual number of craters and an estimated rate of their formation, this age was estimated at around 500 million years.

1 This randomness met statistical tests, but a human test was also performed: Subjects were given the actual Venus crater map and several random plots produced by computer. No-one was able to tell one from the other.