Did the asteroid that wiped out the dinosaurs have a sibling? Crater in West Africa hints maybe.
A likely asteroid impact crater from the latter days of the dinosaurs has been discovered off the coast of West Africa, raising questions about whether the asteroid that wiped out the dinos may have had a smaller sibling that struck around the same time.
The crater, hidden under about 3,000 feet (900 meters) of water and 1,300 feet (400 m) of sediment, hasn't been directly studied yet; it's only been detected in reconstructions of the ocean bed made using seismic waves. To prove beyond a shadow of a doubt that the crater is indeed from an asteroid, scientists will need to drill into the structure and find minerals shocked by extreme heat and pressure. But the crater's shape does point to an extraterrestrial origin, said David Kring, principal scientist at the Lunar and Planetary Institute who was not involved in the current study but was one of the discoverers of the Chicxulub impact site, the crater left by the asteroid that killed the nonavian dinosaurs about 66 million years ago.
"I have to congratulate the team for finding what looks like a probable impact crater," Kring told Live Science. "That's very important, because we have so few impact craters preserved on the Earth. Every single one that we can find provides a new window, new insights into the geological processes that shape them and their effects on biological evolution of Earth."
The new crater was formed very close in time to the Chicxulub impact, raising the possibility that the two may be related. ...
When Uisdean Nicholson, a geologist at Heriot Watt University in the U.K., and his team started poring through seismic data from the West Coast of Africa, they weren't looking for signs of space rocks. ...
To the researchers' surprise, on the seafloor about 250 miles (400 kilometers) from the coast of Guinea and Guinea -Bissau, they found evidence of an odd divot in the rock layers.
"The crater is very striking, and unlike anything that I had ever seen before," Nicholson said.
What the researchers were seeing was a roughly circular or elliptical hole around 5.3 miles (8.5 km) from rim to rim and up to 131 feet (40 m) from floor to rim. The crater's edge revealed signs of faulting and rock deformation, and perhaps even material thrown out of the main crater that landed around it after the impact. One of the telltale features was a structure under the crater floor where the rock layers were raised above their surroundings. This "central uplift" happens after impacts where the shock pressure is high enough to force the grains in the rock to act like a fluid, Nicholson said; the rock essentially sloshes apart, splashes back together and is frozen in that configuration ever after. ...
The researchers dubbed the structure the Nadir crater after a nearby seamount and reported their findings today (Aug. 17) in the journal Science Advances (opens in new tab).
The crater would have been caused by an asteroid that was 1,213 feet (400 m) wide — roughly the height of the Empire State Building. It would have been a bad day to be a fish. The asteroid hit the ocean bed with the power of 5,000 megatons of TNT, the researchers calculated, and it would have produced a fireball 6.2 miles (10 km) wide. This would have instantly vaporized massive amounts of water and rock. The impact would have created a magnitude-7 earthquake that could have kicked off a series of submarine landslides, all of which would have created some serious waves. The splash at the impact site would have towered at least 1.2 miles (2 km), Nicholson said, and the waves that reached the West African coastline may have been 62 miles (100 km) high. The South American coast, 621 miles (1,000 km) away at the time, would have seen 16-foot-high (5 m) tsunamis. ...