From Wikipedia: An impact event is the collision of a large meteorite, asteroid, comet, or other celestial object with the Earth or another planet. Throughout recorded history, hundreds of minor impact events (and exploding bolides) have been reported, with some occurrences causing deaths, injuries, property damage or other significant localised consequences.
An impact event in an ocean or sea may create a tsunami (a giant wave), which can cause destruction both at sea and on land along the coast.The latest major impact event occurred in Kaali, Estonia about 700 BC, creating the Kaali crater.Impact events have been a plot and background element in science fiction since knowledge of real impacts became established in the scientific mainstream.
Recent prehistoric impact events:
n addition to the extremely large impacts that happen every few tens of millions of years, there are many smaller impacts that occur more frequently but which leave correspondingly smaller traces behind. Due to the strong forces of erosion at work on Earth, only relatively recent examples of these smaller impacts are known. A few of the more famous or interesting examples are:
- Barringer Crater in the USA, the first crater to be proven the result of an impact, ~50,000 years old.
- the Rio Cuarto craters in Argentina, produced by an asteroid striking Earth at a very low angle, ~10,000 years old.
- the Lonar crater lake in India, which now has a flourishing semi-tropical jungle around it, ~52,000 years old (though a study published in 2010 gives a much greater age).
- the Henbury craters in Australia (~5,000 years old), and Kaali craters in Estonia (~2700 years old), apparently produced by objects which broke up before impact.
Modern impact events:
The 1994 impact of Comet Shoemaker-Levy 9 with Jupiter served as a “wake-up call”, and astronomers responded by starting programs such as Lincoln Near-Earth Asteroid Research (LINEAR), Near-Earth Asteroid Tracking (NEAT), Lowell Observatory Near-Earth Object Search (LONEOS) and several others which have drastically increased the rate of asteroid discovery.
In 1998, two comets were observed plunging into the Sun in close succession. The first of these was on June 1 and the second the next day. A video of this, followed by a dramatic ejection of solar gas (supposedly unrelated to the impacts), can be found at the NASA website. Both of these comets evaporated before coming into contact with the surface of the Sun. According to a theory by NASA Jet Propulsion Laboratory scientist Zdeněk Sekanina, the latest impactor to actually make contact with the Sun was the “supercomet” Howard-Koomen-Michels on August 30, 1979. (See also sungrazer.)
On October 7, 2008, a meteoroid labeled 2008 TC3 was tracked for 20 hours as it approached Earth and as it fell through the atmosphere and impacted in Sudan. This was the first time an object was detected before it reached the atmosphere and hundreds of pieces of the meteorite were recovered from the Nubian Desert.
On July 19, 2009, a new black spot about the size of Earth was discovered in Jupiter’s southern hemisphere by an amateur astronomer. Thermal infrared analysis showed it was warm and spectroscopic methods detected ammonia. JPL scientists confirmed that another impact event on Jupiter had occurred, probably a small undiscovered comet or other icy body.
Between January and May 2010, Hubble’s Wide Field Camera 3 took images of an unusual X shape originated in the aftermath of the collision between asteroid P/2010 A2 with a smaller asteroid.
Mass extinctions and impacts:
In the past 540 million years there have been five generally accepted, major mass extinctions that on average extinguished half of all species. One of the largest mass extinction to have affected life on Earth was in the Permian-Triassic, which ended the Permian period 250 million years ago and killed off 90% of all species; life on Earth took 30 million years to recover.
The cause of the Permian-Triassic extinction is still matter of debate with the age and origin of proposed impact craters, i.e. the Bedout High structure, hypothesized to be associated with it are still controversial.
The last such mass extinction led to the demise of the dinosaurs and coincided with a large meteorite impact; this is the Cretaceous–Tertiary extinction event (also known as the K–T extinction event); This occurred 65 million years ago. There is no definitive evidence of impacts leading to the four other major mass extinctions.
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