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Impact Craters
When a massive asteroid strikes Earth, it leaves a giant crater which may yield meteorites, pieces of the original asteroid, transformed by the massive pressure and excessive temperature conditions caused by impact. One of the largest craters on Earth, the Morokweng Crater of Africa, formed 145 million years ago and measures 70 kilometers across. Wolfgang Maier, a researcher from the University of Quebec, examined the melt sheet -- liquefied rock caused by an asteroid striking the ground with terrifying force. The scientist found a 25-cm-diameter meteorite within the melt sheet, defying the theory that asteroids vaporize upon impact.
Mega-tsunamis
About 4,800 years ago, an asteroid struck the Indian Ocean, causing a mega-tsunami, or monster wave, measuring 600 feet in height, flooding the region of Madagascar. The wave left V-shaped deposits called chevrons containing substances only found at the bottom of oceans. Within the chevrons, scientists discovered embedded fossils of marine creatures. Dallas Abbott, a scientist with the Lamont-Doherty Earth Observatory in New York, located the site of the impact -- 18 miles across -- deep beneath the ocean. Other groups of scientists, including Ted Bryant of the University of Wollongong in Australia, have provided additional evidence supporting the regular occurrences of mega-tsunamis in response to asteroid impacts in the oceans.
Temperature Changes
Massive asteroid impacts have had profound effects on global temperatures for long periods of time. When the asteroid that supposedly caused the extinction of the dinosaurs hit Earth around 65 million years ago, the temperature decreased on a global scale -- called an "impact winter" -- because of the dust kicked up into the atmosphere, blocking the sun's rays. Plants died because they lacked the sunlight to make their own food. With the demise of plant life, animal life soon followed, causing worldwide extinctions. Carbon dioxide levels then rose dramatically, creating a "greenhouse effect" that kept heat from escaping into space. Temperatures worldwide soared 10 degrees Celsius above average, killing off additional species.
Mass Extinctions
One of the most recent asteroid impact events occurred approximately 65 million years ago at the K-T, or Cretaceous-Tertiary, boundary -- marking the end of the Cretaceous and the beginning of the Tertiary period of Earth's history. The Chicxulub Crater near the Yucatan Peninsula of present-day Mexico may represent the impact crater caused by such an asteroid.
Scientists tested samples of rock, finding evidence of a massive impact event from the iridium found at the site. The element iridium, while rare on Earth, occurs naturally in space objects such as asteroids. Mass extinctions, which happened five times in Earth's history, occurred when great numbers of species disappeared from the planet in a relatively short amount of time. During the K-T extinction, more than 50 percent of all life died, including most marine organisms and all dinosaur species.
Origin of Life
Based on examination of asteroids orbiting in the asteroid belt, scientists theorized that the origin of all life on Earth may have occurred in outer space. Andrew Rivkin, an astronomer with the Johns Hopkins University Applied Physics Laboratory in Maryland, found both water and organic compounds on the surface of the asteroid, 24 Artemis. Scientists hypothesized that the turbulent atmosphere of ancient Earth would have melted away any water and destroyed the bonds of any organic molecules existing on the planet; therefore, other sources would have had to replenish the depleted supplies of water and molecules. A logical source of water and organic compounds would have been the asteroids.