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[Topic] The professor explains that there are two theories to explain the sudden disappearance of dinosaurs 65 million years
[Topic] The professor explains that there are two theories to explain the sudden disappearance of dinosaurs 65 million years
admin
2012-01-14
52
问题
W: Now, class, I’m sure you’ve read and heard a lot about the extinction of the
dinosaurs, which occurred about 65 million years ago. People are fascinated
by this topic, probably because we have yet to determine its cause. Why did
these giant reptiles, who had ruled the planet for millions of years, suddenly
disappear? Well, the theories are endless, but I’d like to talk about two that
are the most plausible. The first is known as the Impact Theory, and I’d say it’s
the most widely supported. According to this concept, there was a very large
asteroid-like object that collided with Earth. The results were catastrophic:
enormous explosions, earthquakes, tsunamis, raging forest fires...But
most importantly, an impact of that magnitude would have thrown up large
amounts of dust into the sky, so much that it would’ve prevented sunlight
from reaching the surface. According to the theory, plants would have died
first from the lack of light, and then this decline worked its way up the food
chain, until the extinction of the dinosaurs was complete. As I said, it’s a very
well-supported theory, but there’s another one, and it’s called the Volcano-
Greenhouse Theory. This idea holds that there was a significant increase
in volcanic eruptions 65 million years ago. These eruptions released large
amounts of carbon dioxide into the atmosphere, creating a greenhouse effect
and causing temperatures on Earth to rise. Now, this wasn’t enough to kill
the dinosaurs immediately. What happened, according to the theory, was that
the heated environment made it impossible for dinosaur embryos to survive.
Female dinosaurs were unable to produce offspring, and, well, you can see
how that would lead to the extinction of species.
选项
答案
[Topic] The professor explains that there are two theories to explain the sudden disappearance of dinosaurs 65 million years ago. [Example 1] One is called the impact theory. It’s a widely supported theory, and it suggests that dinosaurs died out after an asteroid impact. When a gigantic asteroid collided with Earth, the sky was darkened with dust, and sunlight couldn’t get through the dust cloud. As a result, plants died, the entire food chain suffered, and dinosaurs eventually died out. [Example 2] The other is called the volcano-greenhouse theory. It explains that there was a big increase in volcanic eruptions. The eruptions threw a lot of carbon dioxide into the atmosphere, and this produced a greenhouse effect. The Earth’s temperature warmed, and it became so hot that dinosaurs were no longer able to reproduce, which of course led to their extinction.
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