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 seas 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 sea to the land was perhaps as much of an evolutionary challenge as was the genesis of life.
What forms of life were able to make such a drastic change in lifestyle? The traditional view of the first terrestrial organisms is based on mega fossils-relatively large specimens of essentially whole plants and animals. Vascular plants, related to modern seed plants and ferns, left the first comprehensive megafossil record. Because of this, it has been commonly assumed that the sequence 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 closer look at the sediments below this Silurian-Devonian geological boundary.
It turns out that some fossils can be extracted from these sediments by putting the rocks in an acid bath. The technique has uncovered new evidence from sediments 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.pushed
These newly discovered fossils have not only revealed the existence of previously unkno
wn organisms, but have also pushed back these dates for the invasion of land by multicellular organisms. Our views about the nature of the early plant and animal communities are now being revised. And with those revisions come new speculations about the first terrestrial life-forms.
29. The word "drastic" in line 5 is closest in meaning to
(A) widespread
(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 seas.
32. The word "extracted" in line 18 is closest in meaning to
(A) located
(B) preserved
(C) removed
(D) studied
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 closest in meaning to
(A) methods
(B) processes
(C) cases
(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 closest 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 revised.
(B) Old techniques for analyzing fossils were found to have new uses.
(C) The origins of primitive sea life were explained.
(D) Assumptions about the locations of ancient seas were changed.

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