单选题
The human species came into being at the time of the
greatest biological diversity in the history of the Earth. Today, as human
populations expand and alter the natural environment, they are reducing
biological diversity to its lowest level. The ultimate consequences of this
biological reduction are beyond calculation, but they are certain to be harmful.
That, in essence, is the biodiversity crisis. The history of
global diversity can be summarized as follows: after the initial flowering of
multi-cellular animals, there was a swift rise in the number of species in early
Paleozoic times (between 600 and 430 million years ago), then plate-alike
stagnation for the remaining 200 million years of the Paleozoic era, and finally
a slow but steady climb through the Mesozoic and Cenozoic eras to diversity's
all-time high. This history suggests that biological diversity was hard won and
a long time in coming. Furthermore, this pattern of increase was set back by
five massive extinction episodes. The most recent of these, during the
Cretaceous period, is by far the most famous, because it ended the age of the
dinosaurs, giving hegemony to the mammals, thus ultimately making possible the
dominance of the human species over the Earth. But the Cretaceous crisis was
minor compared with the Permian extinctions 240 million years ago, during which
between 77 and 96 percent of marine animal species perished. It took five
million years, well into Mesozoic times, for species diversity to begin a
significant recovery. Within the past 10,000 years biological
diversity has entered a wholly new era. Human activity has had a devastating
effect on species diversity, and the rate of human-induced extinctions is
accelerating. Half of the bird species of Polynesia have been eliminated through
hunting and the destruction of native forests. The list of such biogeographic
disasters is extensive. Because every species is unique and
irreplaceable, the loss of biodiversity is the most profound process of
environmental change. Its consequences are also the least predictable because
the value of the Earth's species remains largely unstudied and unappreciated;
unlike material and cultural wealth, which we understand because they are the
substance of our everyday lives, biological wealth is usually taken for granted.
This is a serious strategic error, one that will be increasingly regretted as
time passes.
单选题
What is TRUE about the Cretaceous crisis according to the author?
A.It was the most famous devastating extinction episode in history.
B.It is the most devastating extinction episode up until now.
C.It was less devastating to species diversity than is the current
biodiversity crisis.
D.The dinosaurs comprised the great majority of species that perished during
the crisis.