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the dinosaurs of their chief food supply. Small omnivorous mammals could have
gotten by with scavenging.
The impact theory was suggested seven years ago by physicist Luis
Alvarez of Lawrence Berkeley Laboratory, who found high concentrations of
the element iridium in clay throughout the world, deposited Just when the
dinosaurs vanished. Iridium is rare on earth but is richly concentrated in comets
and meteors. That suggested an impact occurred, and that its force was enough
to eject a dust cloud that settled over the globe.
Hew researchers at the U.S. Geological Survey in Denver have bolstered
Alvarez's theory. Bruce Bohor and coworkers examined the crystal structure of
quartz particles from the similar clay deposits at seven sites. In every instance,
the quartz showed signs of being struck by an enormous shock wave. The only
other places such shocked quartz is found are known meteor- impact craters and
underground nuclear-test sites.
Volcanic eruptions also give off high concentrations of iridium, and had
been suggested as an alternative explanation for Alvarez's discoveries. But
volcanoes pack too little punch to shock quartz grains. A meteor 6 miles across,
on the other hand, striking the earth at 45,000 miles per hour, would release as
much energy as several billion atomic bombs. The resulting prehistoric nuclear
winter could have sent the dinosaur to oblivion.
Notes:
literally буквально
omnimorous всеядный
eruption извержение
Text 14
GATORS AND CROCS
Croeodilians have few enemies. True and false.
Baby alligators and crocodiles have many enemies. They are eaten by
raccoons, otters, wading birds, big fish, snakes and turtles; also by many other
kinds of larger animals, including bigger alligators and crocodiles.
If they live long enough to grow up, they have no enemies except people.
But with such an enemy they really don't need any others. People have destroyed
many of the animals' homes, filling them in with soil or garbage and building
houses there. Great numbers of baby alligators have been captured .and sold as
pets. Millions of larger ones have been killed for their thick, leathery skins,
which have been made into shoes, handbags, luggage and belts.
The number of alligators and crocodiles alive today is very small compared
to the number just 100 years ago. Crocodilians "talk" to each other. True.
52
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