英语听力：探索发现 科学新发现：我们的大气层-8（在线收听） |
Our planet was spared this fate. The magnetic field generated by the Earth’s core blocked the solar wind, preventing it from blasting away the fragile air. But the Earth’s atmosphere was still very different from the one we breathe today. It contained high level of carbon dioxide, a chemical with a key ability to absorb and hold on to heat. Carbon dioxide still makes up 95 percent of Venus’ atmosphere. It superheated our twin planet to the point where its water boiled away into space. And yet this didn’t happen on Earth. David crisp believes that was down to a chance event.
If Earth kept all of its initial atmosphere, it probably would have turned out a lot more like Venus. But that didn’t happen. We were victims of a very lucky accident.
Earth’s big break came four and a half billion years ago. Back then, the solar system wasn’t limited to the 8 planets it has today. Instead, a swarm of proto-planets or planetesimals orbited the sun like bees around a honey pot. One Mars-sized body was heading straight for Earth. In a colossal cosmic collision, it slammed into our planet, creating our moon and according to Crisp, removing the atmosphere that still blights Venus. This ancient event was defining moment for our atmosphere. With the original deadly gas mix blasted away, our planet’s air could slowly evolve into what it is today. |
| 原文地址：http://www.tingroom.com/lesson/yytltsfx/2014/284448.html |