Unit3 SectionⅡ-【精讲精练】2023-2024学年高中英语选择性必修第一册北师大版（教师用书）

Section Ⅱ　Lesson 1 原文呈现 THE SIXTH EXTINCTION Extinctions, where entire species are wiped out①， are not unusual②in our Earth's history.In fact，over 90 percent of all species that ever lived are now extinct.In the last 500 million years，there have been five times when life on Earth has almost ended.These include the third mass extinction, known as the “Great Dying”，which killed 90% to 96% of all species.[画线部分中“known as the‘Great Dying’”为过去分词短语作后置定语，与which 引导的非限制性定语从句共同修饰the third mass extinction。]And the fifth event, which occurred 66 million years ago，caused the death of the dinosaurs.The reasons for extinctions are varied③.According to scientists, they include volcanic eruptions④， asteroids⑤ hitting the Earth from space，[v.­ing复合结构作include的宾语，下文中的“forests being destroyed”也是同样的结构。]changes in sea levels，the decrease⑥ of the oxygen content of the sea and global warming.Many scientists say we are now entering the Earth's sixth mass extinction.This time, human activity will be to blame⑦. Although it is not unusual for species to die out naturally, the rate⑧ at which this is now happening[“介词＋关系代词”引导的定语从句，修饰the rate。介词at的选用是考虑到与rate搭配。] is cause for concern⑨.A 2015 study by scientists who were based at⑩ Brown University and Duke University in the US, looked at⑪ how quickly species die out due to natural causes, that is, the “background extinction rate”．They found that human activity is causing species to die out 1,000 times faster than normal.There is a long list of reasons why so many species are dying out：[why引导的定语从句，修饰reasons，why在从句中作状语。]air and water pollution, forests being destroyed，factory farming⑫ and overfishing⑬.It is clear that human activity has negatively affected⑭ all other species on Earth, including animals and plants. If a sixth mass extinction occurs，[If引导的条件状语从句]scientists who have studied the issue[who引导的定语从句，修饰scientists] believe that up to three quarters of all species on Earth could die out.Of course, as we humans depend on so many species for our