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英语阅读生命的起源
The Genesis of Life
keywords: Life's transition, lifestyle, terrestrial organisms, Vascular plants, the mega fossils, multicellular, paleontologists
Life originated in the early as less than a billion years after the Earth was formed. Yet another three billion years were to pass before the first plants and animals appeared on the continents. Life's transition from the a to the land was perhaps as much of an evolutionary challenge as was the genesis of life.
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What forms of life were able to make such a drastic change in lifestyle? The traditional view of the first terrestrial organisms is bad on mega fossils-relatively large specimens of esntially whole plants and animals. Vascular plants, related to modern ed plants and ferns, left the first comprehensive megafossil record. Becau of this, it has been commonly assumed that the quence of terrestrialization reflected the evolution of modern
terrestrial ecosystems. In this view, primitive vascular plants first colonized the margins of continental waters, followed by animals that fed on the plants, and lastly by animals that preyed on the plant-eaters. Moreover, the mega fossils suggest that terrestrial life appeared and diversified explosively near the boundary between the Silurian and the Devonian periods, a little more than 400 million years ago. Recently, however, paleontologists have been taking a clor look at the diments below this Silurian-Devonian geological boundary.
It turns out that some fossils can be extracted from the diments by putting the rocks in an acid bath. The technique has uncovered new evidence from diments that were deposited near the shores of the ancient oceans-plant microfossils and microscopic pieces of small animals. In many instances the specimens are less than one-tenth of a millimeter in diameter. Although they were entombed in the rocks for hundreds of millions of years, many of the fossils consist of the organic remains of the organism.
The newly discovered fossils have not only revealed the existence of previously unkno
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wn organisms, but have also pushed back the dates for the invasion of land by multicellular organisms. Our views about the nature of the early plant and animal communities are now being revid. And with tho revisions come new speculations about the first terrestrial life-forms.
29. The word "drastic" in line 5 is clost in meaning to
(A) widespread给自己鼓掌
(B) radical
(C) progressive
(D) risky
30. According to the theory that the author calls "the traditional view," what was the first form of life to appear on land?
(A) Bacteria
(B) Meat-eating animals
(C) Plant-eating animals
(D) Vascular plants
31. According to the passage, what happened about 400 million years ago?
(A) Many terrestrial life-forms died out.
(B) New life-forms on land developed at a rapid rate.
(C) The megafossils were destroyed by floods.
(D) Life began to develop in the ancient as.
32. The word "extracted" in line 18 is clost in meaning to
(A) located
(B) prerved
(C) removed
(D) studied
官眼33. What can be inferred from the passage about the fossils mentioned in lines 17-20?
(A) They have not been helpful in understanding the evolution of terrestrial life.
(B) They were found in approximately the same numbers as vascular plant fossils.
(C) They are older than the megafossils.
(D) They consist of modern life forms.
34. The word "instances" in line 21 is clost in meaning to
(A) methods
(B) process
(C) cas
(D) reasons
35. The word "they" in line 22 refers to
(A) rocks
(B) shores
(C) oceans
(D) specimens
36. The word "entombed" in line 22 is clost in meaning to
(A) crushed
(B) trapped
(C) produced
(D) excavated
37. Which of the following resulted from the discovery of microscopic fossils?
(A) The time estimate for the first appearance of terrestrial life-forms was revid.
(B) Old techniques for analyzing fossils were found to have new us.
(C) The origins of primitive a life were explained.
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(D) Assumptions about the locations of ancient as were changed.
38. With which of the following conclusions would the author probably agree?
(A) The evolution of terrestrial life was as complicated as the origin of life itlf.幼儿指南
(B) The discovery of microfossils supports the traditional view of how terrestrial life evolved.
商品推广(C) New species have appeared at the same rate over the cour of the last 400 million years.
(D) The technology ud by paleontologists is too primitive to make accurate determinations about ages of fossils.
