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Fig. 6.2
The curve of a predominant paradigm
a predominant paradigm and its citation profile. A paradigm normally shows as a
cluster of documents instead of a single, isolated spike. Documents that survived a
paradigm shift might well become obliterated.
6.3
The Mass Extinction Debates
Five mass extinctions occurred in the past 570 million years on earth. Geologists
divided this vast time span into eras and periods on the geological scale (See
Tab le
6.2
). The Permian-Triassic extinction 248 million years ago was the greatest
of all the mass extinctions. However, the Cretaceous-Tertiary extinction, which
wiped out the dinosaurs from the earth 65 million years ago within a short period of
time along with many other species, has been the most mysterious and hotly debated
topic over the last two decades.
6.3.1
The KT Boundary Event
Dinosaurs' extinction occurred at the end of the Mesozoic. Many other organisms
became extinct or were greatly reduced in abundance and diversity. Among these
were the flying reptiles, sea reptiles, and ichthyosaurs, the last disappearing slightly
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