A．there is a consensus about the causes of the end-Perm……
TEXT D
Disaster struck 250
million years ago, when the worst devastation in the earth’s history occurred.
Called the end-Permian mass extinction, it marks a fundamental change in the
development of life.
The history of life on the earth is replete
with catastrophes of varying magnitudes. The one that has captured the most
attention is the extinction of the dinosaurs and other organisms 65 million
years ago between the Cretaceous and Tertiary periods--which claimed up to half
of all species. As severe as that devastation was, it pales in comparison to the
greatest disaster of them all: the mass extinction some 250 million years ago,
at the end of the Permian period. Affectionately called "the mother of
mass extinctions" among paleontologists (with apologies to Saddam Hussein), it
yielded a death toll that is truly staggering. About 90 percent of all species
in the oceans disappeared during the last several million years of the Permian.
On land, more than two thirds of reptile and amphibian families vanished.
Insects, too, did not escape the carnage: 30 percent of insect orders ceased to
exist, marking the only mass extinction insects have ever undergone.
But from catastrophes, opportunities arise. For several hundred million
years before the end-Permian event, the shallow seas had been dominated by
life-forms that were primarily immobile. Most marine animals lay on the seafloor
or were attached to it by stalks, filtering the water for food or waiting for
prey. In the aftermath of the extinction, many once minor groups-active,
predatory relatives of modern-day fish, squids, snails and crabs —were able to
expand. Some completely new lineages appeared. This ecological reorganization
was so dramatic that it forms a fundamental boundary in the history of life.
Not only does it demarcate the Permian and Triassic periods, it also
establishes the close of the Paleozoic era and the start of the Mesozoic era.
The modern tidal pool reflects what lived and what died 250 million years
ago.
Over the past few years, exciting new insights into the
causes and consequences of the end-Permian mass extinction have poured in from
virtually every branch of the earth sciences Some of these findings include
detailed studies of rapid changes in ocean chemistry, more thorough
documentation of extinction patterns and new analyses showing that large
volcanic eruptions occurred at the Permo-Triassic boundary.
How
much do mass extinctions contribute to the evolution of a group, as compared
with long-term adaptive trends For example, sea urchins are ubiquitous in
modern oceans but were relatively uncommon during the Permian. Only a single
genus, Miocidaris, is known for certain to have survived the extinction. Did
Mioeidaris survive by pure chance, or was it better adapted Would sea urchins
today look any different had it not been for the end-Permian
extinction
To resolve such questions, we need to learn more
about the causes of the catastrophe and how those species that survived differed
from those that disappeared. The key sources for this information are rock
layers and fossils. Unfortunately, samples from the late Permian and early
Triassic are notoriously difficult to come by. The fossil record across the
boundary is plagued by poor preservation, a lack of rock to sample and other
problems, including access. An extensive drop in sea level during the late
Permian limited the number of marine rocks deposited on land, and many areas
where the best rocks were preserved (most notably, in southern China) have been
relatively hard for some geologists to reach.
As such, it has
proved difficult to ascertain just how quickly life was snuffed out or if the
deaths were subject to any regional variations. Some creatures, especially those
sensitive to changes in the environment, died off rapidly, as shown by Erik
Flugel and his colleagues at the University of Erlangen, who arrived at this
conclusion after examining reefs in southern China and Greece. Other evidence
indicates more gradual loss of life.
Intensive studies of newly
found and critical boundary layers in Italy, Austria and southern China have
helped our understanding. They indicate that the duration of the extinction is
shorter than previously thought, implying that abruptly calamitous environmental
conditions must have set in.
We can conclude from the passage that ______.
A．there is a consensus about the causes of the end-Permian mass extinction
B．man would not have existed without the end-Permian mass extinction
C．insects are more adaptable in coping with natural devastations
D．natural catastrophes must have hindered the evolution of life
