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The uncertainty of science: Scientists doing geothermal research in Australia have discovered evidence of what they think is the largest known impact zone from an meteorite on Earth.
The zone is thought to be about 250 miles across, and suggests the bolide split in two pieces each about 6 miles across before impact. The uncertainty is that the evidence for this impact is quite tentative:
The exact date of the impacts remains unclear. The surrounding rocks are 300 to 600 million years old, but evidence of the type left by other meteorite strikes is lacking. For example, a large meteorite strike 66 million years ago sent up a plume of ash which is found as a layer of sediment in rocks around the world. The plume is thought to have led to the extinction of a large proportion of the life on the planet, including many dinosaur species.
However, a similar layer has not been found in sediments around 300 million years old, Dr Glikson said. “It’s a mystery – we can’t find an extinction event that matches these collisions. I have a suspicion the impact could be older than 300 million years,” he said.
In other words, they find some evidence that an impact occurred, but not other evidence that is expected to be found with such an impact. Moreover, the rocks at the sedimentary layer where the impact is found are dated around 300 million years ago, a time when no major extinction took place. Either this impact didn’t really happen, or it didn’t happen when it appears it should have, or it shows that large impacts don’t necessarily cause mass extinctions.