Q1.
The rare element, iridium, was presented both on earth and in meteorites.
Q2.
The meteor impact theory had been suspected before the discovery of the impact site and other
supporting evidence.
Q3.
Footprints are of little value in providing information, in comparison to fossil bones, because individual
species cannot be identified with footprints.
Q4.
According to scientists, the transition to a dinosaur-dominated era took place very quickly by geological
time scales.
Q5.
The creatures that disappeared in the extinction were the dominantly the 15-foot-long rauisuchians and
large crocodiles.
Q6.
Tyrannosaurus rex was larger in body size than other carnivorous dinosaurs.
Q7.
Large dinosaurs died out but small ones evolved and competed with birds and mammals.
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QUESTION-TYPE BASED TESTS
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TEST 4 - The Dinosaurs Footprints and Extinction
A.
EVERYBODY
knows that the dinosaurs were killed by an asteroid. Something big hit the earth 65
million years ago and, when the dust had fallen, so had the great reptiles. There is thus a nice, if ironic,
symmetry in the idea that a similar impact brought about the dinosaurs' rise. That is the thesis proposed by
Paul Olsen, of Columbia University, and his colleagues in this week's Science.
B.
Dinosaurs first appear in the fossil record 230m years ago, dining the Triassic period. But they
were mostly small, and they shared the earth with lots of other sorts of reptile. It was in the subsequent
Jurassic, which began 202million years ago, that they overran the planet and turned into the monsters
depicted in the book and movie “Jurassic Park”. (Actually, though, the dinosaurs that appeared on screen
were from the still more recent Cretaceous period.) Dr Olsen and his colleagues are not the first to suggest
that the dinosaurs inherited the earth as the result of an asteroid strike. But they are the first to show that the
takeover did, indeed, happen in a geological eyeblink.
C.
Dinosaur skeletons are rare. Dinosaur footprints are, however, surprisingly abundant. And the
sizes of the prints are as good an indication of the sizes of the beasts as are the skeletons themselves. Dr
Olsen and his colleagues therefore concentrated on prints, not bones.
D.
The prints in question were made in eastern North America, a part of the world then full of rift
valleys similar to those in East Africa today. Like the modem African rift valleys, the Triassic /Jurassic
American ones contained lakes, and these lakes grew and shrank at regular intervals because of climatic
changes caused by periodic shifts in the earth's orbit. (A similar phenomenon is responsible for modem ice
ages.) That regularity, combined with reversals in the earth's magnetic field, which are detectable in the tiny
fields of certain magnetic minerals, means that rocks from this place and period can be dated to within a few
thousand years. As a bonus, squish lake-edge sediments are just the things for recording the tracks of
passing animals. By dividing the labour between themselves, the ten authors of the paper were able to study
such tracks at 80 sites.
E.
The researchers looked at 18 so-called ichnotaxa. These are recognizable types of footprint that
cannot be matched precisely with the species of animal that left them. But they can be matched with a
general sort of animal, and thus act as an indicator of the fate of that group, even when there are no bones to
tell the story. Five of the ichnotaxa disappear before the end of the Triassic, and four march confidently
across the boundary into the Jurassic. Six, however, vanish at the boundary, or only just splutter across it;
and three appear from nowhere, almost as soon as the Jurassic begins.
F.
That boundary itself is suggestive. The first geological indication of the impact that killed the
dinosaurs was an unusually high level of iridium in rocks at the end of the Cretaceous, when the beasts
disappear from the fossil record. Iridium is normally rare at the earth's surface, but it is more abundant in
meteorites. When people began to believe the impact theory, they started looking for other Cretaceous-end
anomalies. One that turned up was a surprising abundance of fern spores in rocks just above the boundary
layer—a phenomenon known as a “fern spike”
G.
That matched the theory nicely. Many modem ferns are opportunists. They cannot compete
against plants with leaves, but if a piece of land is cleared by, say, a volcanic emption, they are often the first
things to set up shop there. An asteroid strike would have scoured much of the earth of its vegetable cover,
and provided a paradise for ferns. A fem spike in the rocks is thus a good indication that southing terrible
has happened.
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