It was one of the most destructive days in the history of our planet, and now we know how it played out. Scientists have pieced together the first day of the dinosaurs’ extinction, by drilling into the crater(火山口)that formed from the asteroid(小行星)that caused their downfall.
The asteroid, which led to the extinction of all dinosaurs that can’t fly, crashed into the Gulf of Mexico’s Yucatan Peninsula some 66 million years ago. In 2016, a scientific drilling project by the International Ocean Discovery Program got rocks from the impact site, which has been underwater for a long time. Now, scientists have analysed these rocks to travel back in time to that particular day itself.
“It’s an expanded record of events that we were able to recover from within ground zero,” said Dr Sean Gulick, a geophysicist at the University of Texas at Austin and leader of this study. “It tells us about impact processes from an eyewitness location.”
In just 24 hours following the impact, a layer of material 130m thick was deposited. This include charcoal, which provides evidence for the intense wildfires that are thought to have been caused by the crash.
Meanwhile, the impact also led to a huge tsunami, an extremely large wave in the sea caused by an earthquake, as evidenced by layers of rocks and sand in the core samples, which appear to have been deposited by flooding waters.
One thing conspicuously missing from the samples, though, is the element of sulphur(硫磺). Although the surrounding area is full of sulphur-rich rocks, the crater is unusually sulphur-free. This supports the idea that the asteroid impact instantly vaporised sulphurous rocks, releasing the sulphur into the atmosphere, where it remained and reflected away the Sun’s light, cooling the Earth’s climate.
Although the impact had destructive effects on a regional level, it’s this large-scale global cooling that’s thought to be behind the dinosaurs’ eventual extinction, as well as that of countless other plant and animal species.
“The real killer has got to be atmospheric,” said Gulick. “The only way you get a global mass extinction like this is an atmospheric effect.”
【小题1】Dr Sean Gulick is quoted in paragraph 3 in order to ______.| A．stress the impact of the crash |
| B．illustrate the significance of their study |
| C．explain what they did in their study |
| D．state the reason for dinosaurs’ death |
| A．obviously | B．restlessly | C．occasionally | D．potentially |
| A．The tsunami. |
| B．The wildfires. |
| C．The vapourised sulphur. |
| D．The deposit of rocks. |
| A．Touching on the dinosaur’s time |
| B．Drilling into the day the dinosaurs died |
| C．Why we need to study the atmospheric effect |
| D．What we should know about the history of our planet |
