Scientists have found evidence of an asteroid impact crater beneath the north Atlantic ocean.
The 8.5km-wide crater is buried 300-400m below the seabed 400km off the coast of Guinea, west Africa.
The team believes the crater was caused by a 400m-wide asteroid colliding with Earth around 66 million years ago - around the same time that the Chicxulub asteroid hit Earth and wiped out the dinosaurs.
But they'll need to drill into the seabed and collect samples to prove their theory.
If confirmed, the crater will be one of less than 20 confirmed marine impact craters found on Earth.
The discovery is reported in Science Advances.
What does the crater look like?
Dr Uisdean Nicholson, a geologist at Heriot-Watt University in Edinburgh, found the crater by examining seismic reflection from the seabed of the Atlantic.
“I've interpreted lots of seismic data in my time but had never seen anything like this. Instead of the flat sedimentary sequences I was expecting on the plateau, I found an 8.5km depression under the seabed, with very unusual characteristics.
“It has particular features that point to an asteroid. It has a raised rim and a very prominent central uplift, which is consistent for large impact craters.
“It also has what looks like ejecta outside the crater, with very chaotic sedimentary deposits extending for tens of kilometres outside of the crater.
“The characteristics are just not consistent with other crater-forming processes like salt withdrawal or the collapse of a volcano.”
Nicholson has named it the Nadir crater, after a nearby seamount.
The asteroid crashed around same time as the dinosaur killer
The seismic data also indicates that the sediments impacted by the asteroid correspond with the Cretaceous-Paleogene boundary. However, there is some uncertainty because of the resolution of the seismic data.
This is the same age as the dinosaur-killing Chicxulub crater. The team believes the asteroid that created the newly-discovered Nadir crater could have formed by the break-up of a parent asteroid or by a flux of asteroids at that time period.
Dr Sean Gulick, an impact expert at the University of Texas at Austin, said: “The Nadir Crater is an incredibly exciting discovery of a second impact close in time to the Cretaceous–Paleogene extinction.
“While much smaller than the extinction causing Chicxulub impactor, its very existence requires us to investigate the possibility of an impact cluster in the latest Cretaceous.”
“Despite four billion years of impactors hitting Earth, only 200 have been discovered. It is thus exciting news whenever a new potential impact is discovered, especially in the hard-to-explore marine environment.”
What impact would the crater have had?
The scientists used computer simulations to determine what kind of collision took place and what the effects might have been.
Dr Veronica Bray, a planetary scientist at the University of Arizona, said: “Our simulations suggest this crater was caused by the collision of a 400m-wide asteroid in 500-800m of water.
“This would have generated a tsunami over one kilometre high, as well as an earthquake of magnitude 6.5 or so.
“The energy released would have been around 1000 times greater than that from the January 2022 eruption and tsunami in Tonga.
“These are preliminary simulations and need to be refined when we get more data, but they provide important new insights into the possible ocean depths in this area at the time of impact.
Nicholson has already applied for funding to drill into the seabed and confirm that it's an asteroid impact crater and test its precise age.
Read the report in full at Science Advances.