Grove Karl Gilbert
The great American geologist who argued that the Moon's craters were made by impacts, yet concluded that Meteor Crater was not.
Key facts
- Born
- 1843
- Died
- 1918
- Nationality
- American
- Field
- Geologist
Grove Karl Gilbert was one of the founders of modern geology in the United States. He worked for the US Geological Survey for most of his life, became its chief geologist, and wrote classic studies of mountains, rivers, ancient lakes and earthquakes.
In 1891, after Albert Foote reported meteoritic iron around a crater in Arizona, Gilbert went to investigate. He reasoned that if a huge iron had made the crater, it should lie buried beneath the floor, so the crater should contain more mass than the material thrown out, and a buried iron should disturb a compass needle. His measurements found no extra mass and no magnetic effect. He concluded that the crater was made by a steam explosion and that the irons nearby were a coincidence.
We now know his reasoning failed because a meteorite striking at many kilometres per second is largely destroyed, vaporised and scattered in the explosion. There was never a giant buried mass to find.
Yet Gilbert came closer than anyone of his time on a larger question. In 1892 he studied the Moon through a telescope in Washington and argued, in a paper published the next year, that its craters were made by impacts rather than volcanoes. He even did experiments, firing balls into clay and mud. Almost nobody agreed with him, but he was right.
On the timeline
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The Canyon Diablo meteoriteBarringer Crater (Meteor Crater) crater