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SUMMARY
On iridium, eruptions
and asteroids
by
Kristinn J. Albertsson
Department of Geosciences
University of Iceland
IS-101 REYKJAVÍK
lceland
This paper gives a resumé of the dec-
ade’s most popular hypothesis in the earth
sciences and attempts to present the two
major schools of thought. Towards the
end of the Mesozoic Era drastic environ-
mental changes occurred throughout the
world. Whole regions were submerged
while others surfaced from the sea. To-
gether with these environmental changes
about 70% of all living species are thought
to have died out (Surlyk 1980). The most
spectacular change was that dinosaurs, the
largest land animals ever to live on this
earth, disappeared together with their
close relatives, both winged and ntarine
reptiles. The mesozoic cephalopods, am-
monites and belemnites which had been
characteristic for the world seas through-
out the Mesozoic died out, together with
whole families of gastropods, echinoids,
large bivalves and much of planktonic life.
Curiously enough there were, however,
ntany groups of animals that were little af-
fected, crocodiles, snakes, and mammals
and a large selection of invertebrates. An-
giosperms had been introduced during the
Cretaceous and flowering plants devel-
oped rapidly at the beginning of the Terti-
ary. Insects enjoyed a rapid evolution and
the evolution of placental mammals was
nothing short of explosive.
Just over ten years ago a group of
American scientists (Alvarez et al. 1980)
put forward a hypothesis that might ac-
count for the mass extinction at the
boundary between the Cretaceous and
Tertiary periods. They had set out to date
13