Our planet has suffered countless impacts over its history. Take the 150km-wide (93-mile) Chicxulub crater buried beneath the Yucatán Peninsula in Mexico.
The colossal impact which caused that is thought to have contributed to the mass extinction of life on Earth 66 million years ago.
Or Meteor Crater in the desert of northern Arizona.
At just over 1km (0.6 miles) wide and only around 50,000 years old, it’s a particularly fresh scar.
In fact, in the last million years or so, there have been five far more sizeable impacts, with the Zhamanshin crater being the largest and most recent of them.
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How Zhamanshin formed... and changed
The Zhamanshin impact structure was formed around 870,000 years ago in Kazakhstan.
Unlike pristine craters – for example, on the Moon – its topography has been substantially altered, even in the relatively brief time since its formation.
One possible reason is flooding from the nearby Aral Sea. Whatever the cause, the true extent of the crater is far from clear by looking at the landscape.
Studies by a Russian geological expedition in 1989, and subsequent analyses of photographs of the region in the decades since, have estimated Zhamanshin’s outer rim to be around 13km (8 miles)
in diameter.
But now James Garvin, a planetary scientist at the NASA Goddard Space Flight Center, and his colleagues say this could be a gross underestimate.
A much bigger bang
Garvin and his team have used modern Digital Elevation Models (DEMs) to examine the terrain.
Created from radar, laser scans or stereo pictures, they precisely depict a landscape with a resolution
of just a few metres.
Working with five different DEMs of Zhamanshin, they discovered convincing evidence of an outer rim to the crater with a diameter of around 26.6km (16.5 miles) – over twice as large as the previous estimates.
This is significant because the blasting of a crater twice as big requires a great deal more impacting energy – perhaps as much as 10 times more – and so would have had much greater environmental consequences.
The exact scenario depends on details such as the density and velocity of the impactor, but Garvin’s team have calculated the likely effect.
The Zhamanshin impact melted or vaporised around 10 cubic kilometres (2.4 cubic miles) of the target rock, with over half of it being flung well beyond the crater.
A fine dusting of impact sediment around half a metre thick would have settled up to 1,500km (932 miles) from the impact site.
Overall, the impact would have released energy equivalent to an explosion of over 240,000 million tonnes of TNT – around 16 million times greater than the nuclear bomb dropped on Hiroshima, and over 1,000 times more than the Krakatoa volcanic eruption in 1883 that caused severe tsunamis and lowered global temperatures for years.
They believe the Zhamanshin impact would have had significant regional effects – including triggering widespread fires – as well as likely global consequences.
These include an ‘impact winter’ (from the lofted particles blocking sunlight), acid rain and depletion of the ozone layer.
And this raises a very interesting question: did such a significant, recent impact have detectable effects on Earth’s ecosystems at the time?
Lewis Dartnell was reading The Zhamanshin Impact Event: Potential Implications for Environmental Responses and Biological Linkages on Earth and Beyond by James B Garvin et al. Read it online at: arxiv.org/abs/2604.04884
