原文已被隐藏，你可用 快捷键 - 或点击 显示原文 按钮来查看原文
第1段
1 .<-NARRATOR:-> Now Listen to part of a lecture in an environmental studies class.
该句暂无译文！
第2段
1 .<-FEMALE PROFESSOR:-> What happens, biologically speaking,
该句暂无译文！
2 .when a major climate change occurs?
该句暂无译文！
3 .Well, scientists generally agree that the extinction of various animal or plant species
该句暂无译文！
4 .is one very likely effect.
该句暂无译文！
5 .This has happened in the past.
该句暂无译文！
6 .An example is the disappearance 35,000 years ago
该句暂无译文！
7 .of a giant Australian bird called the thunder bird.
该句暂无译文！
8 .Now these birds were so big that they couldn't fly.
该句暂无译文！
9 .[finding the thread again] But as I was saying, uh...right...many scientists are convinced
该句暂无译文！
10 .that it was a change in climate that caused this species to become extinct.
该句暂无译文！
第3段
1 .Here's the evidence,
该句暂无译文！
2 .here's why scientists think it was climate change:
该句暂无译文！
3 .[pause] researchers have discovered an enormous number of 35,000 year-old thunder bird bones,
该句暂无译文！
4 .all together in one spot¡ª
该句暂无译文！
5 .the bones were found near an ancient, dried up lake.
该句暂无译文！
6 .Now it's really rare to find so many bones from the same species in one place,
该句暂无译文！
7 .but there it is: you have all
该句暂无译文！
8 .these 35,000-year-old thunder bird bones, all together near this dried up lake.
该句暂无译文！
9 .So what's the explanation?
该句暂无译文！
第4段
1 .Well, many scientists believe
该句暂无译文！
2 .that a change in the Australian climate
该句暂无译文！
3 .may be behind this ...
该句暂无译文！
4 .Their hypothesis is...
该句暂无译文！
5 .they think that during a very long dry period,
该句暂无译文！
6 .when there was no rainfall,
该句暂无译文！
7 .the birds may have flocked together at this lake.
该句暂无译文！
第5段
1 .You see, during a drought, animals tend to gravitate
该句暂无译文！
2 .toward the last few remaining water sources.
该句暂无译文！
3 .But then, if it still doesn't rain, if the drought lasts too long,
该句暂无译文！
4 .the water source
该句暂无译文！
5 .may dry up, too,
该句暂无译文！
6 .and if that happens, the animals that have gathered there, well, they die.
该句暂无译文！
第6段
1 .Scientists think this
该句暂无译文！
2 .ancient lake where they found the bones was one of the last remaining sources of fresh water
该句暂无译文！
3 .during the drought, so
该句暂无译文！
4 .that's where all these birds gathered.
该句暂无译文！
5 .They survived there for a time,
该句暂无译文！
6 .but eventually the lake dried up,
该句暂无译文！
7 .and well, that was it.
该句暂无译文！
8 .By the time the drought ended, the species was extinct.
该句暂无译文！