What is the impact theory of dinosaur extinction?

The impact theory is one of the newest ideas in the catastrophic camp of dinosaur extinction. This theory states that a large object (or objects), such as an asteroid or comet, collided with Earth, resulting in a large impact crater, giant waves in the oceans that smashed onto land at heights of two to three miles (3.2 to 4.8 kilometers), and radical, rapid changes in Earths weather, temperature, amount of sunshine, and climate.

What are asteroids and comets?

An asteroid is a large rocky body found in outer space. They range from boulder size all the way up to about 600 miles (965 kilometers) wide; they generally are classified as either carbonaceous, stony, or metal. The majority of asteroids are found along the plane, or ecliptic, of the solar system. The larger ones are sometimes called minor planets because of their propensity to orbit along the same plane as the major planets. Most of the asteroids revolve around the Sun in a tight band between the orbits of Mars and Jupiter, called the asteroid belt. Italian astronomer Giuseppe Piazzi (1746-1826) discovered the first asteroid, Ceres, in 1801.

Comets are a collection of dust, gases, and ice that orbit the Sun. Once described as dirty snowballs, many comets are now thought to be more like mud- balls, most carrying more dust than ice. In general, comets are composed of carbon dioxide, frozen water, methane, ammonia, and materials such as silicates and organic compounds.

Where are asteroids and comets found in our solar system?

The majority of the asteroids stay within the asteroid belt, a band of chunks of rock between the orbits of Mars and Jupiter. Short-period comets, or those with orbits from a few to 200 years, are thought to have originated in the Kuiper Belt, a fat disk of comet-like objects beyond the orbit of Neptune and Pluto. Long-term comets, or those that travel into the solar system every few thousand years (or may never return at all), are thought to originate in the Oort Cloud, a theoretical cloud of comets proposed by Dutch astronomer Jan Oort (1909-1992). The cloud surrounds the solar system about 100,000 astronomical units from the Sun (one astronomical unit is equal to about 93 million miles [149,637,000 kilometers], the average distance between Earth and the Sun).

What are near-Earth objects?

Over hundreds of thousands of years, because of the gravitational pull of the planets or other space objects, an asteroid or comet may stray from the belt. Such space objects mostly asteroids that come close to Earth or cross Earths orbit are called near-Earth asteroids (the ones that cross Earths path are also called Earthcrossing asteroids). It is known that in the past some near-Earth asteroids struck Earth, creating impact craters on the planets surface. Meteor Crater in Arizona is a good example of an impact crater formed by an asteroid. There also seems to be an association between some of the larger Earth impact craters and the extinction of a large number of species during the planets long history.

Scientists currently believe there are about 2,000 near-Earth objects, (mostly asteroids or burned-out comets) larger than a half mile (one kilometer) in diameter that revolve around the Sun in short-period orbits. These objects can occasionally intersect the orbit of Earth; but most of the time, we pass right by each other or we are far from each other when the object crosses Earths orbit. The only problem is that scientists believe that only about 7 to 10 percent of this estimated population has been discovered. Although hampered by funding cuts, scientists continue to search the sky for these potential hazards. Therefore, we do not know the actual orbits of most of these near-Earth objects.

One of the theories about dinosaur extinction that has gained favor is that a large asteroid struck Earth, dramatically changing the environment. Today, astronomers are tracking near-Earth objects in order to prevent a similar fate from befalling us (iStock).

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