Passage 2 Life
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 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 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
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 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.
These newly discovered fossils have not only revealed the existence of previously unknown
organisms, but have also pushed back these dates for the invasion of land by multi-cellular
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.
【題組】46. 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