Mysterious crater may have been created by relatives of dinosaur-killing asteroid

Mysterious crater may have been created by relatives of dinosaur-killing asteroid

How craters form.Credit: Provided by the author

As we all know, the exploration of the seabed is not as good as the surface of Mars. When our team of scientists recently mapped the seabed and ancient sediments below, we found what looked like an asteroid impact crater.

Interestingly, the crater, named “Nadir” after the nearby volcano Nadir Seamount, is the same age as the Chicxulub impact from a huge asteroid at the end of the Cretaceous period, about 66 million years ago, when dinosaurs and dinosaurs went extinct. many other species.

The finding, published in the journal Science Advances, raises the question of whether the crater may be somehow related to Chicxulub. If confirmed, it would also have enormous general scientific interest, as it would be one of very few known oceanic asteroid impacts, and thus could provide unique new insights into what happens during such a collision.

The crater was identified using “seismic reflections” as part of a broader project to reconstruct the tectonic separation of South America from Africa during the Cretaceous period. Seismic reflections work in a similar way to ultrasonic data, sending pressure waves through the ocean and its seafloor and detecting the energy reflected back. These data allow geophysicists and geologists to reconstruct the structure of rocks and sediments.

As we scrolled through the data in late 2020, we discovered a very unusual feature. In the flat layered sediments of the Guinea Plateau in western Africa, there appears to be a huge crater, less than 10 kilometers wide and hundreds of meters deep, buried in hundreds of meters of sediment.

Many of its features are consistent with impact origins, including the size of the crater, its aspect ratio, and the height of the crater rim. The chaotic deposits on the crater floor also looked like “ejections” — material expelled from the crater immediately after a collision.

We did consider other possible processes that could have formed such a crater, such as the collapse of a submarine volcano or a salt column (or diapir) under the seabed. The explosive release of subsurface gases may also be a cause. But none of these possibilities fit the local geology or the geometry of the crater.

Earthquakes, air blasts, fireballs and tsunamis

After identifying and characterizing the crater, we built a computer model of the impact event to see if we could replicate the crater and characterize the asteroid and its impact.

The best simulation for the shape of the crater is an asteroid 400 meters in diameter hitting an ocean 800 meters deep. The consequences of an impact in such a deep ocean are dramatic. This would cause an 800-meter-thick column of water, as well as the immediate evaporation of the asteroid and a lot of sediment—a large fireball visible hundreds of kilometers away.

The impact produced shock waves equivalent to a magnitude 6.5 or 7 earthquake, which could trigger underwater landslides around the area. A series of tsunami waves will form.

The blast of air from the blast would be bigger than anything heard on Earth in recorded history. The energy released is about a thousand times that of Tonga’s recent eruption. Pressure waves in the atmosphere also have the potential to further amplify tsunami waves farther away from the crater.

Mysterious crater may have been created by relatives of dinosaur-killing asteroid

Nadir Meteor Crater.Credit: Provided by the author

Chicxulub relatives?

One of the most interesting aspects of this crater is that it is the same age as the giant Chicxulub event at the junction of the Cretaceous and Paleogene 66 million years ago, about a million years old. Also, if this is really an impact crater, is there some kind of relationship between them?

We have three ideas for their possible relationship. The first is that they may have formed from the breakup of the parent asteroid, with the larger fragment leading to the Chicxulub event, and the smaller fragment (“little sister”) forming the nadir crater. If so, the destructive effects of the Chicxulub impact may have been increased by the nadir impact, thereby exacerbating the severity of the mass extinction event.

The splitting event may have formed from an earlier approach collision, when an asteroid or comet came close enough to Earth to experience a gravitational force strong enough to pull it apart. The actual collision may have occurred in subsequent orbits.

While this is unlikely for a rocky asteroid, this pull-off is exactly what happened to Comet Shoemaker-Levy 9, which collided with Jupiter in 1994. Over the course of a few days, multiple comet fragments were linked to the asteroid. Planets collide.

Another possibility is that the nadir is part of a longer-lived “impact cluster” that was formed by a collision in the asteroid belt early in the history of the solar system. This is known as the “little cousin” hypothesis.

The collision may have sent a burst of asteroids into the inner solar system that could collide with Earth and other inner planets over an extended period of time, possibly a million years or more. We have precedents for such events as far back as the Ordovician period, more than 400 million years ago, when many impact events occurred in a short period of time.

In the end, of course, this could just be a coincidence. We do expect a nadir-sized asteroid collision every 700,000 years or so. For now, however, we cannot definitively show that Nadir crater was formed by an asteroid impact until we physically recover samples from the crater floor and identify minerals that can only be formed by extreme shock pressures. To that end, we recently submitted a proposal to drill the crater through the International Ocean Discovery Program.

As with the major impact crater hypothesis, we can only test the sister and younger cousin hypothesis by using these samples to accurately date the crater, and by looking for other candidate craters of similar age.

Perhaps more importantly, will such an event happen in the near future? This is unlikely, but the size of the asteroid we modeled is very similar to the Bennu asteroid currently in low Earth orbit. The 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 in the next few centuries.

More than one asteroid could spell doom for dinosaurs

More information:
Uisdean Nicholson et al., Nadir Crater, Offshore West Africa: A Candidate Cretaceous-Paleogene Impact Structure, scientific progress (2022). DOI: 10.1126/sciadv.abn3096

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