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ZoomDinosaurs.com
Dinosaur and Paleontology Dictionary
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

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THE K-T EXTINCTION

About 65 million years ago, at the end of the Cretaceous, a large fraction of plant and animal families suddenly went extinct. In this Cretaceous-Tertiary or K-T mass extinction (K is for Kreide, meaning chalk in German, which describes the chalky sediment layer from that time; T is for Tertiary, the next geologic period), all land animals over about 55 pounds went extinct, as did many smaller organisms.

There are a lot of theories about why the K-T (Cretaceous-Tertiary) extinction occurred, but a widely accepted theory (proposed in 1980 by physicist Luis Alvarez and his son Walter Alvarez, a geologist), is that an asteroid 4-9 miles (6-15 km) in diameter hit the Earth about 65 million years ago, creating the Chicxulub crater at the tip of Mexico's Yucatán Peninsula. The impact would have penetrated the Earth's crust, scattering dust and debris into the atmosphere, and causing huge fires, tsunamis, severe storms with high windsand highly acidic rain , seismic activity, and perhaps even volcanic activity . The impact could have caused chemical changes in the Earth's atmosphere, increasing concentrations of sulfuric acid, nitric acid, and fluoride compounds. The heat from the impact's blast wave would have incinerated all the life forms in its path.

The Shiva crater is a another huge impact crater located under the Arabian Sea off the coast of India near Bombay. This crater also dates from the K-T boundary, 65 million years ago, when the Chicxulub crater at the tip of the Yucatán Peninsula also formed. Although theShiva crater has shifted because of sea floor spreading, when pieced together it would be about 370 miles (600 km) by 280 miles (450 km) across and 7.5 miles (12 km) deep (and may be just part of a larger crater). It is estimated to have been made by a bolide (an asteroid or meteoroid) 25 miles (40 km) in diameter. This crater was named by the paleontologist Sankar Chatterjee for Shiva, the Hindu god of destruction and renewal.

The dust and debris thrust into the atmosphere would have blocked most of the sunlight for months, and lowered the temperature globally.

The K-T mass extinction obliterated the dinosaurs , pterosaurs, plesiosaurs, mosasaurs, ammonites, some families of birds and marsupial mammals, over half the plankton groups, many families of teleost (bony) fishes, bivalves, snails, sponges, sea urchins and others.

This catastrophe eventually led to the Age of Mammals.

During the K-T extinction, it has been estimated that 80-90% of marine species, about 50% of the marine genera, and about 15% of the marine families went extinct. For land animals, about 85% of the species, about 25% of the families, and about 56% of the genera died out. Larger animals (over about 55 pounds=25 kg) were all wiped out.


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