Top 5 Asteroids That Have Impacted on Earth

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Remnants of the original material that formed the solar system, asteroids by the millions zip around the sun at extremely high speed. Compared to full-fledged planets, these fragments are extremely small, and only a handful can be seen with the naked eye. Asteroids frequently cross the Earth's orbital path, however, and on rare occasions strike the planet, an event that can bring devastation to a wide area as well as a significant change in global climate.

5 The Chesapeake Bay Crater

The most recent discovery of a large-impact crater took place in the early 1980s in Chesapeake Bay, Maryland, just 125 miles from Washington DC. This "marine impact" occurred in a tidal region of the North American coast about 35 million years ago, creating a huge fracture in the underlying bedrock, a crater about 53 miles wide, and a tsunami that may have reached the Blue Ridge Mountains, 150 miles to the west.

4 Diamonds from the Sky

The Popigai crater in northern Siberia may have been the world's most valuable asteroid impact. This event, dated to about 36 million years ago, created a flash of light and heat intense enough to create a hemispheric zone of diamond-bearing rock from a layer of graphite, approximately 12 kilometers from the point of impact. Because the heat and pressure were of short duration, however, geologists believe this deposit is not of gemstone quality; Popigai has not been mined yet because industrial diamonds have become cheaper to manufacture in a laboratory.

3 The Chicxulub Impact

The famed Chicxulub crater that formed 65 million years ago along the Yucatan Peninsula was the product of an asteroid about 10 kilometers wide striking the earth at an estimated speed of 50,000 miles an hour. The impact threw up a cloud of dust that choked the planet's atmosphere for several years. Paleontologists have dated a mass extinction of the dinosaurs to about the same time, leading many scientists to theorize that a global change in climate caused by the Chicxulub impact contributed to the "K-T Event," the demise of 70 percent of all species on Earth.

2 Ontario's Sudbury Basin

The Sudbury Basin in Ontario runs a close second to the Vredefort Dome in size and age. Scientists date this structure—30 kilometers wide and 15 kilometers deep—to an asteroid impact that occurred 1.8 billion years ago. The object's size and speed allowed it to penetrate the Earth's crust, bringing molten rock to the surface. This material flooded cracks and fissures in the bedrock, and left behind a wealth of valuable minerals. The Sudbury Basin is a major source of nickel and copper and is now home to the world's largest concentration of mines.

1 The Vredefort Event

Although an estimated 2 billion years has passed since the Vredefort impact, geologists have very clear evidence of the event, in the form of a crater and uplift structure in South Africa with a radius of 118 miles. Investigators estimate the asteroid to have been 10 kilometers in diameter; creating the largest impact meteorite structure yet found on Earth. (In space parlance, a meteorite is any extra-terrestrial object, including an asteroid, that falls to earth.)