Английская Википедия:Eltanin impact
Шаблон:Short description Шаблон:Infobox terrestrial impact site
The Eltanin impact is thought to be an asteroid impact in the eastern part of the South Pacific Ocean that occurred around the Pliocene-Pleistocene boundary approximately 2.51 ± 0.07 million years ago.[1] The impact occurred at the north edge of the Bellingshausen Sea Шаблон:Convert southwest of Chile, where the sea floor is approximately Шаблон:Convert deep.[2] The asteroid was estimated to be about Шаблон:Cvt in diameter. No crater associated with the impact has been discovered.[3] The impact likely evaporated Шаблон:Cvt of water, generating large tsunami waves hundreds of metres high.[4]
Description
The possible impact site was first discovered in 1981 as an iridium anomaly in sediment cores collected by the research vessel Eltanin, after which the site and impactor are named.[5] Later studies were done by the vessel Polarstern.[6] Sediment at the bottom of the Шаблон:Convert deep ocean in the area had an iridium enrichment, a strong sign of extraterrestrial contamination. Possible debris from the asteroid is spread over an area of Шаблон:Convert. Sediments from the Eocene and Paleocene were jumbled and deposited again chaotically. Also mixed in were melted and fragmented meteorite matter. The area near the Freeden Seamounts over Шаблон:Convert has a meteorite material surface density of Шаблон:Cvt. Of this, 87% is melted and 13% only fragmented. This area is the region of the Earth's surface with the highest known density of meteorite material coverage.[2]
The disturbed sediment had three layers. The lowermost layer SU IV is a chaotic mixture of crumbled sediments in the form of a breccia. Above this is layer SU III consisting of layered sand, consistent with having been deposited from turbulently flowing water. Above this is SU II layer with meteorite fragments and graded silt and clay that plausibly settled out of still but dirty water.[7]
Asteroid
The supposed impacting body, the Eltanin asteroid, is estimated to have been between Шаблон:Convert in diameter and traveling with a speed of Шаблон:Convert. The possible size of the asteroid was calculated by the amount of iridium found in the disturbed sediments. Assuming that there were 187 parts per billion of iridium in the asteroid, the known distribution of the metal leads to estimates that the body was over Шаблон:Convert in size.[8] Based on a diameter of one km, it is estimated it would have left a crater about Шаблон:Cvt across.[3]
The composition of suspected asteroid remnants has been classified as low metal mesosiderites.[7] The bolide explosion would also have produced microspherules under half a millimeter in diameter.[9] Some of these are glass, and others have spinel and pyroxene. Elements enriched include calcium, aluminium and titanium.[2]
Tsunami
On the shorelines of the Pacific Ocean there are erosional features that are indicative of a very large tsunami. These include an erosional surface and chaotic deposits of mixed terrestrial and ocean-derived sediment. Boulders as big as buses are mixed with marine fossils and mud. The most well-characterised tsunami deposits are near the coast of Chile. Off the coast of Antarctica there are mudslides into the deep ocean from this age.[10]
The size of a possible tsunami has been calculated. An asteroid that was Шаблон:Convert in diameter falling onto the Шаблон:Convert deep ocean would have blasted the water off the ocean floor for at least Шаблон:Convert, and made a wave over Шаблон:Convert high on the southern end of Chile and the Antarctic Peninsula. After ten hours, waves around Шаблон:Convert would reach Tasmania, Fiji and Central America, and the New Zealand east coast would have been washed with Шаблон:Convert high waves. If the impact object was Шаблон:Convert in diameter, the wave heights would have been one-fifth as great.[3]
Ice age trigger
At the time of the impact in the Late Pliocene, the Earth was cooling. The impact and disruption to the weather could have triggered the start of ice cap formation in the Northern Hemisphere.[11] The impact would have put a large amount of water and salt into the atmosphere, disrupted ice shelves, depleted the ozone layer, caused surface acidification, and increased the Earth's albedo.[12]
See also
- Karakul crater – a large impact crater which may be just a few million years older than Eltanin
- List of possible impact structures on Earth
- Шаблон:Annotated link
References
External links
Шаблон:Impact cratering on Earth Шаблон:Portal bar
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- Hypothetical impact events
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- Pleistocene South America
- Pleistocene impact craters
- Megatsunamis
- Geology of the Pacific Ocean
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