Robert Dietz
The geologist who showed that shatter cones are fingerprints of impacts, and who argued that Sudbury in Canada is a giant impact structure.
Key facts
- Born
- 1914
- Died
- 1995
- Nationality
- American
- Field
- Geologist and oceanographer
Robert Sinclair Dietz was an American marine geologist who worked for the US Navy and government research bodies. He was one of the first to propose, in 1961, that new ocean floor is made at mid-ocean ridges, the idea of seafloor spreading that became part of plate tectonics.
Dietz had a second great interest: impact craters. He noticed that rocks at some ancient structures contained shatter cones, cone-shaped fractures with fine branching grooves, which point towards the place where a shock wave came from. In the 1940s and 1950s he studied shatter cones at the Kentland structure in Indiana and argued that only the shock wave of an impact could make them.
This gave geologists a field test for old, eroded impact structures that no longer look like craters. Using it, Dietz argued in 1964 that the huge Sudbury structure in Ontario, famous for its nickel and copper mines, was made by an impact nearly 2 billion years ago. Shatter cones have since been used to confirm impacts at many sites, including Vredefort in South Africa.
Dietz also campaigned in his later years against pseudoscience, and he named many features, including the term astrobleme, meaning star wound, for an ancient eroded impact scar.
On the timeline
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Sudbury craterVredefort crater