Life is believed to have 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. The transition of life from sea to land was perhaps as significant an evolutionary challenge as the origin of life itself.
(A) 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 megafossils—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 widely assumed that the sequence of terrestrialization mirrored 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 megafossils 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.
(B) 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 rock for hundreds of millions of years, many fossils still contain organic remains.
These newly discovered fossils have not only revealed the existence of previously unknown 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 revised. And with those revisions come new speculations about the first terrestrial life-forms.
1. The word "drastic" in paragraph (A) is closest in meaning to?
2. According to the theory that the author calls "the traditional view" what was the first form of life to appear on land?
3. According to the passage, what happened about 400 million years ago?
4. The word "extracted" in paragraph (B) is closest in meaning to?
5. What can be inferred from the passage about the microscopic fossils discovered below the Silurian-Devonian boundary?
6. The word "instances" in paragraph (B) is closest in meaning to?
7. The word "they" in paragraph (B) refers to?
8. The word "entombed" in paragraph (B) is closest in meaning to?
9. Which of the following resulted from the discovery of microscopic fossils?
10. With which of the following conclusions would the author probably agree?