Crater of Chicxulub

The crater of Chicxulub is according to several scientists a crater caused by the fall of a Météorite of almost 10 kilometers diameter which would have fallen down on the Ground approximately 65 million years ago, i.e. at the end of the Crétacé. An assumption (recently contradicted) known as that its fall would mark the end of the secondary era and would have thus caused one of the massive extinctions which struck the Earth. This assumption seems to be recently called in question. It would seem that 300.000 years would separate the extinction from the dinosaurs of the fall of this gigantic meteorite. This crater would be thus localized with Chicxulub in the north of the Péninsule of Yucatán, Mexico.

The theory

In the years 1980, it was noticed that in certain geological layers, one noted a fine white layer of a few centimetres thickness between the layers of the Cretaceous and the Tertiary sector. One speaks about it under the name of limit Cretaceous-Tertiary sector, limit CT or limit KT. This geological limit, quite visible in certain points of the sphere, has an abnormal iridium rate. This one is rare on ground, but is more abundant in certain meteorites. It was then theorized the fall of a meteorite at this period.

At the same time, the scientists started to think of the concept of “nuclear Hiver”: one world winter several years which a projecting exchange of hundreds of nuclear weapons of the million tons of dust in the atmosphere would cause, and cooling it by a kind of artificial night. By extension, one put forth the assumption of a “winter of impact”, with the similar effects, caused by the fall of a meteorite.

But the crater of this hypothetical meteorite remained to be discovered. A few years later, one discovered the crater of Chicxulub, in Mexico.

The American physicist Luis Walter Alvarez, his son geologist Walter Alvarez, the nuclear chemist Frank Asaro and the paleontologist Helen Michaelont put forth the assumption according to which the fall of this meteorite at the end of the Crétacé, it there has −65 with −63 million years, was the leading cause of a climatic upheaval at the origin of the extinction of the dinosaurs and of a great number of animal species, as well terrestrial as marine.

Effect of the meteorite: theory

When the asteroid disintegrated at the time of the shock, of the pieces of earth's crust were projected into the atmosphere.

Forming a gigantic remains plume, an immense column of ash and quartz crystals, which were to ten km under ground a few moments before, rose more and more quickly in the atmosphere. This plume swelled until reaching a diameter from 100 to 200 km, arrived in the upper atmosphere, then wrapped whole planet. The particles which it conveyed started to fall down on Earth with the energy which they had acquired during their ejection. Crossing the atmosphere at the speeds ranging between 7.000 and 40.000 kilometers per hour, they illuminated the sky, such of the billion shooting stars then quickly carried vast zones of the atmosphere to hundreds of degrees.

They then gradually accumulated on the ground, forming the layer of ashes observed today. The combustion of materials of the plume ignited the vegetation on an enormous surface of the sphere. Moreover there was a shock wave which would have made all it tower of planet in a few hours. All that took part to plunge the whole Planet in the darkness during several years to the manner of a nuclear Hiver.

In the absence of solar light in sufficient quantity, the Photosynthèse stopped. The Végétaux very quickly decayed, followed closely by the herbivores which involved the carnivores in their decline.

At the same time, a great volcanic activity seems to be awaked, perhaps because of crackings of the terrestrial coat under the impact. One estimates that great quantities of oxide of Soufre escaped, transformed by the rains into Acid sulphuric which killed itself most of the marine animal-life.

Why the atmosphere didn't stop this meteorite, contrary to what usually occurs? Because one estimates (according to the crater of impact) his diameter at 10 km, therefore larger than the thickness of the atmosphere itself (the air is very rarefied to 10.000 m). We have an idea his speed if it arrived of beyond the solar system: necessarily more than 11 km/s. In other words, it would have crossed the atmosphere in less than one second : not even of what to slow down it.

Facts

There exists certain a number of facts in support of this theory.

massive Extinction

All reign S confused, nearly six to eight Espèce S on ten disappeared, whose large sauriens the such Dinosaure S. the insects resisted on the other hand well.

The near total of the marine Plankton, key link of the animal and food chain, also disappeared.

Several specialists estimate that this extinction in mass lasted “at most” a few hundred years. Which are the animals which could survive? Perhaps partly those of small size which lived under ground nourishing vegetable remains, like the invertebrates, as those which nourished these invertebrates. It seems that no animal of a mass higher than 20-25 kg did not survive.

Iridium

The meteorite signed its fixed price by an abnormally high concentration of Iridium in the geological Strate S dating from the limit Crétacé - tertiary (i.e. pile at the border between era secondary and tertiary, which it would thus have caused). This metal of the family of the Platine, rather rare on the surface of our planet because heavy, is more abundant in the meteorites, less however that the Nickel and the Fer. One found iridium in abnormal quantity in ten marine and terrestrial sites of the end of the Cretaceous, distributed on all the surface of the sphere.

Shocked Quartz

One finds in extreme cases K-T of the crystals of “shocked” quartz (i.e. having undergone enormous pressures following a violent impact). Contrary to Iridium, they are especially present in North America, around the Gulf of Mexico, which confirms the assumption of a shock in Mexico.

Diamonds and Zircon

Mixed with this quartz, microscopic diamonds and zircon crystals were also discovered. These minerals require strong pressures to appear, and are thus interpreted like a trace of a gigantic shock. They are products of the point of impact itself.

Tektites

Faded tektites (molten silicates of vitreous aspect, produced by an high temperature) are found in the marine sediments of the time, just in lower part of “shocked” quartz, they thus settled right front. Their position is explained by the low speed of ejection of these materials, which come from the zones located near the point of impact, but not immediately below.

The Spinel S Nickel ifères

Spinel S Nickel ifères (mineral the appearance can be related to the Oxydation in the atmosphere of a meteorite rich in nickel), other elements constitute which supports this theory.

The tidal wave

One finds around the Gulf of Mexico, between the layer of tektite (first to be itself deposited) and lay down it Iridium (which settled shortly after), a sandstone bench, signs of an enormous tidal wave produced by the impact.

Synthesis

The fall of a meteorite giantess at the end of the Cretaceous is allowed today by all. The bond between this meteorite and the Extinction of the Cretaceous are discussed on the other hand more. There exists indeed of other theories on the extinction, where the meteorite does not play an exclusive part inevitably. See the article: Extinction of the Cretaceous.

This extinction is not most massive of those which the Earth in the past knew. There was more important of it, there are 245 to 250 million years, at the end of the Permien, therefore of the primary era. Perhaps it was also caused by another meteorite, which one thinks of having found the crater, named Bedout , whose diameter is of 173 km. See the article: massive Extinctions.

See too

External bonds

EXTINCTION OF THE DINOSAURS: The Chicxulub meteorite is not any more one hypothesis working… 300.000 years too early!
Life sciences and the Earth Page devoted to the meteorite of Chicxulub.
World-Sciences Last theories on the extinction of the dinosaurs.
The Great Chicxulub Debate Where detractors and partisans clash.
the death of the dinosaurs Page devoted to research and the discovery of the astroblème of Chicxulub and its consequences.

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