By: April Carson
An asteroid from space struck the Earth's surface 66 million years ago, creating a huge crater beneath the sea and causing widespread devastation. The impact was so great that it led to the mass extinction of the dinosaurs.
It's not an asteroid that doomed the dinosaurs to extinction, but a previously unknown crater 248 miles off the coast of West Africa that was formed at around the same time. The Nadir Crater, as it is known, could alter what we think we know about that cataclysmic event in natural history.
Uisdean Nicholson, an assistant professor at Heriot-Watt University in Edinburgh, discovered the crater while he was reviewing seismic survey data for another project on the tectonic split between South America and Africa. Uisdean found evidence of 400 meters of seabed sediment which concealed the crater.
"As I was looking at the data, I noticed this very unusual crater-like feature," he said. "It had all the characteristics of an impact crater."
The crater is 5 miles wide and is located in the southwestern Indian Ocean, off the coast of Mozambique.
Certainty about the crater being caused by an asteroid strike would require drilling into the crater and testing minerals from the floor, he said. But it has all other indications scientists would expect: the appropriate ratio of width to depth for a crater, along with matching heights for the rims and central uplift.
"The finding of a terrestrial impact crater is always significant since they are quite unusual in the geological record. There are less than 200 confirmed impact structures on Earth, with many more probable candidates that have not yet been confirmed," according to Mark Boslough, a research professor in Earth and Planetary Sciences at the University of New Mexico. He was not involved in this study but agreed that it was most likely caused by an asteroid.
Dr. David Boslough, a research geologist at the University of Manchester who was not involved in the project, said the most notable aspect of this finding is that it represented submarine impact craters, which are uncommon.
"It is also one of the largest confirmed impact craters on Earth, and the fact that it went unnoticed for so long is a testimony to the difficulty of finding them," he told BBC News.
The researchers believe that the asteroid hit with the force of 10 billion atomic bombs. The resulting shockwave would have been large enough to kill all life within a radius of hundreds of miles.
Nicholson believes the crater was formed by an asteroid more than 400 meters (1,300 feet) in diameter smashing into the planet's crust. The crater is 8 kilometers (5 miles) broad and Nicholson thinks it was most likely caused by a rock larger than 400 meters (1,300 feet).
It is spherical in shape and has a volume of roughly one-quarter that of the world's largest asteroid, Chicxulub. It's nevertheless a rather substantial space rock, especially compared to the city-sized asteroid that triggered the 100-mile-wide Chicxulub crater off the coast of Mexico, which caused the mass extinction of much of life on Earth.
"The (Nadir) impact would have had severe consequences locally and regionally, at least across the Atlantic Ocean," Nicholson said.
The "when" and "where" of the disaster would have been determined by global factors like tectonics. There would have been a colossal earthquake (magnitude 6.5 - 7), thus significant ground shaking locally. The air blast would have been heard around the world, and it would have caused enormous damage in the area as a whole.
The tsunami would've been exceptionally large around the crater–about 3,200 feet (1 kilometer) high. Once it reached South America, the wave dissipated to about five meters tall.
The air blast from Impact Winter should have been orders of magnitude more powerful than the Tunguska event's in-air explosion, which flattened a forest across an area of 1,000 square kilometers. "The air blast (that caused the crater off West Africa) would have been orders of magnitude greater."
The crater was created around 66 million years ago, according to data from microfossils in adjacent exploration wells. However, there is still uncertainty about its exact age -- a margin of error of around 1 million years exists.
Nicholson stated that the asteroid strike might possibly be associated with the Chicxulub impact, but then again, it could just be a mere coincidence -- an object of this size collides with Earth every 700,000 years on average.
Finding out the precise age, however, is critical to testing this -- again, only feasible with drilling. "Again, we're talking about a million years or so. Finding out the precise age would allow us to test if this was part of a longer-lived shower of asteroids that hit the Earth over a period of a million years or so."
If the comet had hit Earth, it would have been small in comparison to the Chicxulub impact, he said, but added that it still would have caused a domino effect of other disasters.
Nicholson emphasizes the importance of understanding the nature of the relationship with Chicxulub, as it provides significant insight to what was happening in our solar system at that time. Additionally, this research raises interesting new questions.
"What we really need to do now is go back and look at all the other craters around that time, see if any of them have the same characteristics, and try and piece together a larger picture," he said.
The study was published on Thursday in the journal Science Advances.
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About the Blogger:
April Carson is the daughter of Billy Carson. She received her bachelor's degree in Social Sciences from Jacksonville University, where she was also on the Women's Basketball team. She now has a successful clothing company that specializes in organic baby clothes and other items. Take a look at their most popular fall fashions on bossbabymav.com
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