DETLEV VAN RAVENSWAAY / SCIENCE PHOTO LIBRARY DETLEV VAN RAVENSWAAY / SCIENCE PHOTO LIBRARY
Earth crater, 19th century artwork. Craters on Earth were used by 19th-century astronomers to explain the origin of lunar craters in terms of volcanism. It was not until 1893 that US geologist Grove Karl Gilbert (1843-1918) advanced his theory that lunar craters were caused by impact events, rather than volcanic eruptions.
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