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In-Depth Information
well known, because it has been so difficult to find and decipher the Creta-
ceous time markers on a global scale.
Five sea level oscillations are present in the sedimentary rocks of Late
Cretaceous age in the Vancouver Island region. Are these regional or global
changes? Only by studying rocks of similar age in many other regions could
this be ascertained.
Sea level change and life
Sea level change is certainly an important environmental factor that af-
fected ancient environments, but it may play an even more important role in
governing the nature of life on earth. For more than a century, sea level
change has been considered one of the leading causes of mass extinctions,
which turn out to be the largest-scale evolutionary phenomena that affect
our planet's biota.
Mass extinctions are global catastrophes that have caused large num-
bers of species to become extinct in the geological past. A mass extinction
event can last between a thousand and several million years. There have
been about 15 such events during the last 500 million years of earth history
(the time of skeletonized life on this planet). Five of these are classified as
"major" in that they caused more than half of all species then living to go ex-
tinct. The most destmctive mass extinction ended the Paleozoic Era. The
second most destructive ended the Mesozoic Era, of which the Cretaceous is
the last unit. This "K/T" mass extinction ended the Age of Dinosaurs and
brought the Cretaceous Period to an end as well.
The possible association between sea level change and mass extinction
was recognized early by geologists. More than a century ago, it was noted
that each of the major mass extinctions seemed to have occurred soon after
a sudden and precipitous drop in global sea level. Yet by what mechanism
might a simple drop in sea level have caused planetary death on a global
scale? There is no doubt that several of the major mass extinctions occurred
