A possible impact crater discovered in India may have been caused by the largest meteorite to strike Earth in the past 50,000 years.
The meteorite could have caused a fireball, a massive shock wave and wildfires that would have spread through an area inhabited by people from the Indus valley civilisation thousands of years ago.
“It would have been definitely equivalent to a nuclear bomb, but without the radioactive fallout,” says at Western University in Canada.
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The 1.8-kilometre-wide crater, called the Luna structure, has been known to locals in Gujarat state for some time. Researchers had examined it before in the belief that it was from an impact, but nothing came of these studies. Recently, at the University of Kerala in India and his colleagues returned to conduct more in-depth research.
Geochemical analysis revealed a high proportion of iridium in the soil, which suggests the impactor was probably an iron meteorite. The team also identified other materials characteristic of meteorites, including wüsite, irschsteinite, hercynite and ulvöspinel.
at Auburn University in Alabama, who wasn’t involved in the study, says that while the geochemical analysis appears to match, the team still hasn’t completely proved this is a crater. To do this, they would need to find super-heated rocks that melted due to the energy of the impact, he says.
“It’s not that I’m suspicious that this isn’t a crater, but it would be nice to have the standard line of evidence in shocked materials,” says King.
Such materials are difficult to find, though – and the area where they would be in the Luna structure is usually underwater. Sajinkumar and his colleagues were only able to dig a trench during the very short dry season, but he says they plan to search for shocked materials in future, calling this study “the tip of the iceberg”.
Osinski says despite the lack of shocked materials, he is convinced that the Luna structure is an impact crater due to the other evidence. “The authors have done a great job with the samples that they have,” he says.
Radiocarbon dating of organic material underneath the debris layer from the presumed impact showed the plant material to be about 6900 years old. But in ongoing work that isn’t yet published, Sajinkumar and his colleagues ran optically stimulated luminescence tests on the soil layer, which revealed the last time that the minerals saw sunlight.
These tests, which are on the presumed pieces of the meteorite itself rather than organic matter underneath the debris layer, have refined the date to roughly 4050 years ago, says Sajinkumar. That would put the timing of the impact around the period near the end of the mature phase of the Harappan civilisation in the Indus valley.
The impact would have created a shock wave that reached about 5 kilometres away, says Sajinkumar, and ejected material could have created wildfires that affected a much larger area. Osinski says the ash and particles kicked up by the meteorite would have dimmed the sun in parts of what is now India for days.
“In the near vicinity, it would be a fireball, then complete decimation for kilometres,” he says.
The crater is just over 100 kilometres from the Dholavira archaeological site, which was a Harappan city in this period. “If there were people living in that area, there would have been some serious casualties,” says King.
Sajinkumar says that this might have been the only impact of such magnitude that complex civilisations on Earth have ever witnessed.
Planetary and Space Science
