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The Eltanin impact is thought to be an impact event in the eastern part of the South Pacific Ocean that occurred around the Pliocene-Pleistocene boundary approximately 2.51 ± 0.07 million years ago. The impact occurred at the north edge of the Bellingshausen Sea southwest of Chile, where the sea floor is approximately deep. The asteroid was estimated to be about in diameter. No crater associated with the impact has been discovered. The impact likely evaporated of water, generating large tsunami waves hundreds of metres high.
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.
The composition of suspected asteroid remnants has been classified as low metal . The bolide explosion would also have produced under half a millimeter in diameter. Some of these are glass, and others have spinel and pyroxene. Elements enriched include calcium, aluminium and titanium.
The size of a possible tsunami has been calculated. An asteroid that was in diameter falling onto the deep ocean would have blasted the water off the ocean floor for at least , and made a wave over high on the southern end of Chile and the Antarctic Peninsula. After ten hours, waves around would reach Tasmania, Fiji and Central America, and the New Zealand east coast would have been washed with high waves. If the impact object was in diameter, the wave heights would have been one-fifth as great.
Asteroid
The supposed impacting body, the Eltanin asteroid, is estimated to have been between in diameter and traveling with a speed of . 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 in size. Based on a diameter of one km, it is estimated it would have left a crater about across.
Tsunami
On the shorelines of the Pacific Ocean there are erosional features that are indicative of a very large tsunami. These include an erosion 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.
Ice age trigger
At the time of the impact in the 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. 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.
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