Scientists Say Second Killer Asteroid May Have Struck Earth

（单词翻译）

Scientists are investigating the possibility that a second asteroid¹ hit Earth about the same time as the one believed to have killed off nearly all dinosaur² life.

The investigation³ is linked to a smaller crater⁴ recently discovered in the ocean. Researchers say the crater may have been created by a large asteroid.

Scientists have long believed that a large asteroid hit Earth about 66 million years ago near Mexico's Yucatán Peninsula. They estimate the force of the crash to be equal to the strength of about 10 billion nuclear bombs.

The strike, or impact, is believed to have caused widespread wildfires, earthquakes and huge ocean waves, or tsunamis⁶. Scientists also believe the event caused a release of chemicals into the atmosphere that led to severe cooling.

The climate-changing event is blamed for causing the disappearance⁷ of more than 70 percent of plant and animal life. All dinosaurs⁸ that were not bird-like died out.

That strike created a huge crater about 180 kilometers wide and 900 meters deep.

Researchers say the newly discovered crater, found in the North Atlantic Ocean, is much smaller. It is about 8.5 kilometers wide. It is buried up to 400 meters below the seabed off the coast of Guinea, in West Africa.

Scientists found the crater by using seismic⁹ instruments. Such tools are designed to measure earthquakes and pick up other vibration¹⁰ signals on Earth.

The crater was discovered by Uisdean Nicholson, a geologist¹¹ at Heriot-Watt University in Edinburgh, Scotland. At the time, Nicholson was working on an ocean-mapping project involving seabed spreading. This kind of spreading is what caused the African and American continents to separate over time, leading to formation of the Atlantic Ocean.

"I've interpreted lots of seismic data in my time, but had never seen anything like this," Nicholson said in a statement. He added that he was surprised to see that the data described a huge crater "with very unusual characteristics."

Nicholson said the crater has several elements that suggest it could have been created by an asteroid. But he noted¹² that researchers will need to investigate more before that theory can be confirmed. A team plans to visit the crater to drill into the seabed and collect mineral samples.

The team's findings were recently reported in a study in the publication Science Advances.

Veronica Bray¹³ is another member of the research team. She is a planetary scientist at the University of Arizona. Bray used computer simulations to predict the effects that such an impact would have had.

The simulations suggested the crater was created by a 400-meter asteroid crashing into 500 to 800 meters of water. She said this would have likely caused a 900-meter-high tsunami⁵, as well as an earthquake with a strength of 6.5.

Bray noted the effects of the newly discovered crater would have been much less than the one that hit present day Mexico. But it still would have added "significantly" to local destruction. She said the new discovery makes her wonder whether there are other impact craters¹⁴ that scientists have not yet found.

Nicholson said his team has considered the possibility that both impact craters could be linked. The researchers said they believe the newly discovered crater could have formed by the breakup of a parent asteroid.

Sean Gulick is a crater impact expert at the University of Texas at Austin. He called the find an "exciting" discovery that could lead to further investigations¹⁵ of other possible impacts around the same time period.

"Despite four billion years of impactors hitting Earth, only 200 have been discovered," Gulick said in a statement. "It is thus exciting news whenever a new potential impact is discovered, especially in the hard-to-explore (ocean) environment," he added.

Words in This Story

asteroid – n. a rocky object that goes around the sun like a planet

vibration – n. a shaking movement

interpret – v. to explain of explore the meaning of something

characteristic – n. a typical or noticeable quality that makes one person or thing different from others

sample – n. a small amount of something that gives you information about the thing it was taken from

simulation – n. a creation of something that behaves or looks like something real but is not

significant – adj. important or notable