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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 ALVAREZ ASTEROID IMPACT THEORY

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. The impact would have penetrated the Earth's crust, scattering dust and debris into the atmosphere, and causing huge fires, increasing already active volcanic eruptions , triggering tsunamis, and severe storms with high winds and causing highly acidic rain . 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 (burned up) all the life forms in its path.

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

Those organisms that could not adapt to the temperature and light changes would die out. Since plants' energy is derived from the sun, they would likely be the first to be affected by changes in climate. Many families of phytoplankton and plants would die out, and the Earth's oxygen levels may well have dramatically decreased, both on land and in the oceans, suffocating those organisms which were unable to cope with the lower oxygen levels.

Major changes in the food chain would result from all of these these environmental upheavals. The herbivores (plant eaters) who ate those plants would starve soon after the plants died. Then, at the top of the food chain, the carnivores (meat eaters), having lost their prey, would have to eat each other, and eventually die out. Their large carcasses must have provided smaller animals with food for quite a while.



LOCATION OF THE IMPACT CRATER(S)

There are many impact craters on Earth. A 120-mile-wide (180 km), 1-mile-deep (1600 m) impact crater, Chicxulub, is found at the tip of the Yucatán Peninsula, Mexico, in the Gulf of Mexico. This crater dates back to 65 million years ago, and is probably the site of the K-T meteorite impact. Evidence of K-T period tsunamis all around the Gulf of Mexico has been found.

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 it 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.



CHEMICAL EVIDENCE FOR THE THEORY

In the clay layer from the Cretaceous-Tertiary (K-T) boundary, scientists have found chemical evidence that supports the Alvarez impact theory. The K-T layer consists of the sedimentary deposits that accrued from the end of the Cretaceous period to the beginning of the Tertiary period. It is divided into two layers, the Magic Layer (3 mm thick) and the Ejecta Layer (2 cm thick).



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