Mysterious crater discovered in the ocean could be a new clue to the fate of dinosaurs: ScienceAlert
The ocean floor is notoriously less explored than the surface of Mars. And when our team of scientists recently mapped the seafloor and the ancient sediments below, we discovered what looks like an asteroid impact crater.
Curiously, the crater, named “Nadir” after the nearby volcano Nadir Seamount, is the same age as the Chicxulub impact caused by a huge asteroid in the late Cretaceous period around 66 million years ago, which wiped out the dinosaurs and many other species.
The discovery, published in Scientists progressraises the question of whether the crater could be related to Chicxulub in some way.
If confirmed, it would also be of enormous general scientific interest as it would be one of the very few known marine asteroid impacts and thus yield unique new insights into what happens in such a collision. .
The crater was identified by “seismic reflection” as part of a larger project to reconstruct the tectonic separation of South America from Africa during the Cretaceous period.
Seismic reflection works similarly to ultrasonic data, sending pressure waves through the ocean and its bottom and detecting the energy that is reflected back.
These data allow geophysicists and geologists to reconstruct the architecture of rocks and sediments.
Going through this data at the end of 2020, we came across a very unusual feature.
Among the flat, stratified sediments of the Guinea Plateau in western Africa was what appeared to be a large crater, just under 10 kilometers (6.2 miles) wide and several hundred meters deep, buried under several hundred meters of sediment.
Many of its characteristics are consistent with an impact origin, including crater scale, aspect ratio, and crater rim height. The presence of chaotic deposits outside the crater floor also resembles “ejecta” – material expelled from the crater immediately after a collision.
We considered other possible processes that could have formed such a crater, such as the collapse of an underwater volcano or a pillar (or diapir) of salt under the seafloor. An explosive release of gas below the surface could also be a cause.
But none of these possibilities are consistent with the local geology or crater geometry.
Earthquakes, Airblast, Fireball and Tsunamis
After identifying and characterizing the crater, we built computer models of an impact event to see if we could replicate the crater and characterize the asteroid and its impact.
The simulation that best matches the shape of the crater is that of an asteroid 400 meters in diameter hitting an ocean 800 meters deep.
The consequences of an impact in the ocean at such water depths are dramatic.
This would result in a column of water 800 meters thick, as well as the instantaneous vaporization of the asteroid and a substantial volume of sediment – with a large fireball visible hundreds of kilometers away.
The shock waves from the impact would be equivalent to a magnitude 6.5 or 7 earthquake, which would likely trigger submarine landslides in the area. A train of tsunami waves would form.
The blast of air from the explosion is said to be larger than anything heard on Earth in recorded history. The energy released would be about a thousand times greater than that of the recent Tonga eruption.
It is also possible that pressure waves in the atmosphere further amplify tsunami waves away from the crater.
One of the most intriguing aspects of this crater is that it is the same age as the giant Chicxulub event, roughly a million years ago, on the boundary between the Cretaceous and Paleogene periods ago. 66 million years old.
Again, if this is really an impact crater, could there be a relationship between them?
We have three ideas as to their possible relationship.
The first is that they may have formed from the burst of a parent asteroid, with the larger fragment resulting from the Chicxulub event and a smaller fragment (the “little sister”) forming the Nadir crater.
If so, the adverse effects of the Chicxulub impact could have been added by the Nadir impact, exacerbating the severity of the mass extinction event.
The breakup event could have formed by an earlier near collision, when the asteroid or comet passed close enough to Earth to experience strong enough gravitational forces to pull it apart. The actual collision could then have occurred in a later orbit.
Although less likely for a rocky asteroid, this separation is exactly what happened to Comet Shoemaker-Levy 9 which collided with Jupiter in 1994, where multiple comet fragments collided with the planet for several days.
Another possibility is that Nadir was part of a longer-lived “impact cluster” formed by a collision in the asteroid belt earlier in the history of the solar system. This is called the “little cousin” hypothesis.
This collision may have sent a shower of asteroids into the inner solar system, which may have collided with Earth and other inner planets over a longer period, possibly a million years or more.
We have a precedent for such an event in the Ordovician period – over 400 million years ago – when there were many impact events in a short time.
Well, of course, it might just be a coincidence. We expect a collision of a Nadir-sized asteroid every 700,000 years or so.
At this time, however, we cannot say with certainty that the Nadir crater was formed by an asteroid impact until we physically retrieve samples from the crater floor and identify minerals that cannot be formed only by extreme shock pressures.
To that end, we recently submitted a proposal to drill the crater under the International Ocean Discovery Program.
As with the main impact crater hypothesis, we can only test the little sister and little cousin hypotheses by accurately dating the crater using these samples, as well as looking for other candidate craters of a similar age.
Perhaps more importantly, could such an event occur in the near future? It’s unlikely, but the size of the asteroid we’re modeling is very similar to the Bennu asteroid currently in near-Earth orbit.
This asteroid is considered one of the two most dangerous objects in the solar system, with a one in 1,750 chance of colliding with Earth within the next two centuries.
Uisdean Nicholson, Associate Professor of Geosciences, Heriot-Watt University; Sean Gulick, Research Professor of Geosciences, University of Texas at Austin, and Veronica Bray, Research Scientist, Lunar & Planetary Laboratory, University of Arizona.
This article is republished from The Conversation under a Creative Commons license. Read the original article.