(ORDO NEWS) — The bottom of the ocean has been studied less than even the surface of Mars. And when a team of scientists recently mapped the seafloor and the ancient deposits beneath it, they found what looked like an asteroid impact crater.
This crater, named “Nadir” after the nearby volcano Nadir, is the same age as the site of the impact of the huge asteroid Chicxulub, which occurred at the end of the Cretaceous period, about 66 million years ago. The one that wiped out the dinosaurs and many other species.
The discovery, published in the journal Science Advances, raises the question of whether this crater could somehow be related to Chicxulub.
If confirmed, it would also be of great scientific interest as it is one of the few known asteroid craters on the seafloor. This may give us a new understanding of what happens during such a collision.
The crater was identified using “seismic reflection” as part of a wider project to reconstruct the tectonic space from South America to Africa as far back as the Cretaceous.
Seismic reflection works in a similar way to ultrasonic data, sending pressure waves across the ocean and its floor, detecting the energy that is reflected back.
This data allows geophysicists and geologists to reconstruct the architecture of rocks and sediments.
Looking at this data at the end of 2020, scientists discovered an unusual feature. Beneath several hundred meters of deposits on the Guinea Plateau west of Africa was what looked like a large crater just under 10 kilometers wide and several hundred meters deep.
Many of its features are indicative of an impact origin, including the scale of the crater, the height-to-width ratio, and the height of the crater rims.
The presence of chaotic deposits outside the crater floor also looks like an “ejection” – material ejected from the crater immediately after the impact.
Earthquakes, Air Explosion, Fireball and Tsunami
After identifying and characterizing the crater, computer impact models were built to characterize the asteroid and reproduce its crater.
The model that best fits the shape of the crater suggests an asteroid with a diameter of 400 meters and a collision with an ocean 800 meters deep.
The consequences of an impact in the ocean at such depths are colossal. This will lead to the instantaneous ejection of a water column 800 meters thick, as well as the instantaneous evaporation of the asteroid and a significant amount of sediment.
The large fireball from the explosion will be visible hundreds of kilometers away.
The shock waves would be equivalent to a magnitude 6.5 or 7 earthquake, which would likely trigger underwater landslides in the region. A tsunami plume is formed.
An explosion in the air would be the loudest in the history of mankind. The released energy will be about a thousand times greater than during the eruption of Tonga.
It is also possible that pressure waves in the atmosphere will further amplify tsunami waves away from the crater.
Relative of Chicxulub?
One of the most intriguing aspects of this crater is its age. It dates to the same time span as the giant Chicxulub event 66 million years ago, give or take one million years. Again, if this is indeed an impact crater, could there be some connection between the two?
There are three ideas regarding their possible relationship. First, they could have formed from the breakup of a single large asteroid, with the larger fragment leading to the Chicxulub event, and the smaller fragment (“little sister”) forming the Nadir crater.
If so, then the devastating effects of the Chicxulub impact could have been compounded by the Nadir impact, exacerbating the severity of the mass extinction.
Another possibility is that Nadir was part of a longer-lived “impact cluster” formed by a collision in the asteroid belt in the early history of the solar system. This hypothesis is known as the “younger cousin” hypothesis.
This collision could have sent a shower of asteroids into the inner solar system, where they could have collided with Earth and other inner planets over a longer period of time, possibly a million years or more.
There was a precedent for such an event back in the Ordovician period – more than 400 million years ago – when many collisions occurred in a short period of time.
Finally, of course, it could just be a coincidence. A collision with a Nadir-sized asteroid is expected every 700,000 years or so.
At this point, however, we cannot definitively state that Nadir Crater was formed by an asteroid impact until samples are physically recovered from the crater floor and minerals are identified that can only be formed as a result of extreme impact pressures.
To this end, a proposal was recently put forward to drill the crater as part of the International Ocean Discovery Program.
As with the main impact crater hypothesis, we can test the “younger sister” and “younger cousin” hypotheses only by accurately dating the crater using these samples and by looking for other candidate craters of the same age.
More importantly, could such an event happen in the near future? Unlikely, the size of the asteroid that has been modeled is very similar to the asteroid Bennu currently in Earth orbit.
This asteroid is considered one of the two most dangerous objects in the solar system. The chance of it colliding with Earth in the next couple of centuries is one in 1750.
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