Read the following passage and mark the letter A, B, C or D to indicate the correct answer to each of the questions from 36 to 42.Life originated in the early seas less than a billion years after the Earth was formed. Yet another three billions 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 ...

Read the following passage and mark the letter A, B, C or D to indicate the correct answer to each of the questions from 36 to 42.

Life originated in the early seas less than a billion years after the Earth was formed. Yet another three billions 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 megafossils - relatively large specimens of essential 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 10 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 the 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.

Recently, however, paleontologists have been taking a closer look at sediments below this Silurian- Devonian geological boundary. It turns out that some fossils can be extracted from these sediments by putting the rock 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.

These discovered fossils have not only revealed the existence ofpreviously unknown organisms, but have also pushed back these dates for the invasion of land by multicellular organisms. Our view about the nature of the early plants and animal communities are now being revised. And with those revisions come new speculations about the first terrestrial life-forms

The word "they" refers to ______.