第29套：The Extinction of the Dinosaurs
Paragraph1:Geologists define the boundary between diment layers of the
Cretaceous period(144-65million years ago)and the Paleocene period (65-55million years ago)in part by the types and amounts of rocks and fossils they contain or lack.Before the limit of65million years ago，marine strata are rich in calcium carbonate due to accumulations of fossils of microscopic algae deposited on the a floor.Above the 65-million-year limit，a-floor diments contain much less calcium carbonate,and fossils of veral families of mollusks are no longer found. In continental diments,dinosaur fossils,though frequent before65 million years ago,are totally abnt.By contrast,new families of mammals appear,including large mammals for the first time.
1..According to paragraph1，which of the following is true of Paleocene diments
○They lack fossils from some families of mammals found in Cretaceous diments.
节目策划书○They contain fossils of dinosaurs.
○They contain fossils of some animals that did not exist during the Cretaceous.
○They contain fossils of more kinds of mollusks than are found in Cretaceous diments.
Paragraph2:Scientists wondered for many years about what could have caud the dinosaurs'rapid disappearance at the end of the Cretaceous period,coming up with a great variety of theories and scenarios.For some,it could have been due to unfavorable genetic changes triggered by a dramatic increa by a factor of10，100，
1，000in cosmic-ray particles reaching the Earth after a supernova explosion somewhere in the neighborhood of the solar system.For the high-energy particles to affect life，they would have to get through the protective barrier of the Earth's magnetosphere,the region of the upper atmosphere controlled by Earth's magnetic field.That could have happened if the cloud of particles from the supernova explosion reached the Earth during a period when the magnetosphere was weakened, something that may happen when the Earth's magnetic field changes direction.And we know that the magnetic north and south poles of the Earth switch on the average twice every million years.However,this is not the only possible explanation for dinosaur destruction.
2..The word unfavorable in the passage is clost in meaning to
○Unusual
○Disadvantageous
银龙鱼不吃食
○Sudden
○major
3..The word triggered in the passage is clost in meaning to
带张的成语○Initiated
○intensified
○followed
○aided磅礴
4.Why does the author include the information that the magnetic north and south poles of the Earth switch on the average twice every million years
○To provide evidence showing that Earth's protective barrier is difficult to get through
○To show that it is reasonable to think that particles from a supernova explosion could have reached Earth
○To explain why some scientists believe a supernova explosion may have occurred near our solar system
○To help explain why some scientists have rejected the theory prented in Paragraph2
11月有什么节日5.According to the theory discusd in paragraph2，a weakening of Earth's magnetosphere may have
○caud a supernova to explode near our solar system
○allowed gene-altering particles to reach Earth's surface
○forced Earth's magnetic field to change direction
○allowed clouds of protective particles to escape from Earth's upper atmosphere
Paragraph3：Other theories have raid the possibility of strong climate changes in
the tropics(but they then must be explained).Certainly，if climate changes，the changed distributions of temperature and rainfall modify the conditions that favor one ecosystem over another.
The extinction of a particular family，genus，or species may result from a complicated chain of indirect caus and effects.Over thirty years ago,scientist Carl Sagan quoted one suggestion that the demi of the dinosaurs resulted from the disappearance of a species of fern plant that was important for dinosaur digestion.Other theories involved a worldwide cold wave following the spread of a layer of cold but not very salty water in the world's oceans, which floated on the
surface becau，with its low salinity，the water was less den. 6..AII of the following are mentioned in paragraph3as possible caus for the extinction of the dinosaurs EXCEPT
○a change in the diet of dinosaurs
○a change in the climate of the tropics
珍珠鸟课文○a decrea in global temperatures
○a decrea in deep ocean salinity
7..ln paragraph3，why does the author include the quotation by Carl Sagan
○To explain the connection between dinosaur extinction and the
extinction of other animal species
○To support the claim about species extinction being due to indirect caus and effects
○To show that scientists have revid their ideas greatly in the last thirty years无所不至的意思
衣原体治疗
○To identify the differences between the various theories for the extinction of
dinosaurs
Paragraph4：Proponents of another theory that remains under consideration today postulate that the extinction of the dinosaurs corresponds to a period of inten volcanic activity.It's not a question of just one or even of a thousand eruptions comparable to the explosion of Krakatoa in1883，one of the largest volcanic events in modern times,but rather of a prolonged period of activity.On the Deccan plateau in India，basalt(volcanic)rocks cover more than500，000square kilometers (nearly200，000square miles)，and correspond to massive lava outflows occurring precily at the end of the Cretaceous.This sort of outflow could correspond to volcanic activity similar to the activity that drives a-floor spreading,with lava emerging from elongated fractures in the crust rather than from craters.
8..According to paragraph4，what was one unusual aspect of the volcanic activity at the end of the Cretaceous
