Everything about the Chicxulub Crater totally explained
The
Chicxulub Crater is an ancient
impact crater buried underneath the
Yucatán Peninsula in
Mexico. Its center is located near the town of
Chicxulub, after which the crater is named—as well as the rough translation of the Mayan name, "the tail of the devil." and others debate whether there was a single impact or whether the Chicxulub impactor was one of several that may have struck the Earth at around the same time. Recent evidence suggests that the impactor was a piece of a much larger asteroid that broke up in a collision in distant space more than 160 million years ago. Penfield's job was to use geophysical data to scout possible locations for oil drilling. Within the data, Penfield found a huge underground arc with 'extraordinary symmetry' in a ring 70 kilometers (40 mi) across. He then obtained a
gravity map of the Yucatán made in the 1960s. A decade earlier, the same map suggested an impact feature to contractor Robert Baltosser, but he was forbidden to publicize his conclusion by Pemex corporate policy of the time. Penfield found another arc on the peninsula itself whose ends pointed northward. Comparing the two maps, he found the separate arcs formed a circle, 180 kilometers (111 mi) wide, centered near the Yucatán village
Chicxulub; he felt certain the shape had been created by a cataclysmic event in geologic history.
Pemex disallowed release of specific data but let Penfield and company official Antonio Camargo present their results at the 1981
Society of Exploration Geophysicists conference. That year's conference was underattended and their report attracted scant attention. (Ironically, many experts in
impact craters and the
K-T boundary were attending a separate conference on Earth impacts.) Although Penfield had plenty of geophysical data sets, he'd no rock cores or other physical evidence of an impact. Their evidence included greenish-brown clay with surplus
iridium containing
shocked quartz grains and small weathered
glass beads that looked to be
tektites. Thick, jumbled deposits of coarse rock fragments were also present, thought to have been scoured from one place and deposited elsewhere by a kilometers-high
tsunami likely resulting from an Earth impact. So when Haitian professor Florentine Morás discovered what he thought to be evidence of an ancient volcano on
Haiti, Hildebrand suggested it could be a telltale feature of a nearby impact. Tests on samples retrieved from the K–T boundary revealed more tektite glass, formed only in the heat of asteroid impacts and high-yield
nuclear detonations. Hildebrand contacted Penfield in Apr 1990 and the pair soon secured two drill samples from the Pemex wells, stored in
New Orleans. Hildebrand's team tested the samples, which clearly showed
shock-metamorphic materials.
A team of California researchers including
Kevin Pope, Adriana Ocampo, and Charles Duller, surveying regional satellite images in 1996, found a
sinkhole ring centered on Chicxulub that matched the one Penfield saw earlier; the sinkholes were thought to be caused by
subsidence of the impact crater wall. More recent evidence suggests the actual crater is 300 kilometers (190 mi) wide, and the 180 kilometer ring an inner wall of it.
Impact specifics
The impactor's estimated size was about 10 km (6 mi) in diameter and may have released an estimated 4
zettajoules of energy, equivalent to 100
teratons of
TNT (10
14 tons), on impact. By contrast, the most powerful man-made explosive device ever detonated, the
Tsar Bomba or Emperor Bomb, had a
yield of only 50
megatons, making the Chicxulub impact 2 million times more powerful. Even the largest known explosive volcanic eruption, which released approximately 10 zettajoules and created the
La Garita Caldera, was substantially less powerful than the Chicxulub impact.
Effects
The impact caused some of the largest
megatsunamis in Earth's history. A cloud of dust, ash and steam would have spread from the crater, as the impactor burrowed underground in less than a second. Excavated material along with pieces of the impactor, ejected out of the atmosphere by the blast, would have been heated to incandescence upon re-entry, broiling the Earth's surface and igniting global wildfires; meanwhile,
shock waves spawned global
earthquakes and
volcanic eruptions. The emission of dust and particles could have covered the entire surface of the Earth for several years, possibly a decade, creating a harsh environment for living things to survive in. The shock production of
carbon dioxide caused by the destruction of carbonate rocks would have led to a dramatic
greenhouse effect, and sunlight would have been filtered out by dust particles in the atmosphere.
Photosynthesis by plants would also have been interrupted, affecting the entire
food chain.
Geology and morphology
In their 1991 paper, Hildebrand, Penfield, and company described the geology and composition of the impact feature. The rocks above the impact feature are layers of marl and
limestone reaching to almost 1,000 meters (3,300 ft) in depth. These rocks date back as far as the
Paleocene. Below these layers lie more than 500 m (1,600 ft) of
andesite glass and
breccia. These andesitic
igneous rocks were found only within the supposed impact feature; similarly, quantities of
feldspar and
augite, normally only found in impact-melt rocks, are present, as is
shocked quartz. Along the edge of the crater are clusters of
cenotes or sinkholes, which suggest that there was a water basin inside the feature during the
Tertiary period, after the impact. The paper also noted that the crater seemed to be a good candidate source for the tektites reported at
Haiti.
Origin
On
September 5,
2007 a report published in
Nature proposed an origin for the asteroid that created Chicxulub Crater.
Chicxulub and mass extinction
The Chicxulub Crater lends support to the theory postulated by the late
physicist Luis Alvarez and his son,
geologist Walter Alvarez, that the extinction of numerous animal and plant groups, including
dinosaurs, may have resulted from a
bolide impact. The Alvarezes, at the time both faculty members at the
University of California, Berkeley, postulated that the extinction event roughly contemporaneous with the postulated date of formation for the Chicxulub crater, could have been caused by just such a large impact. This theory is now widely, though not universally, accepted by the
scientific community. Some critics, including
paleontologist Robert Bakker, argue that such an impact would have killed
frogs as well as dinosaurs, yet the frogs survived the extinction event.
Gerta Keller of
Princeton University argues that recent core samples from Chicxulub prove the impact occurred about 300,000 years
before the mass extinction, and thus couldn't have been the causal factor.
The main evidence of such an impact, besides the crater itself, is contained in a thin layer of clay present in the K–T boundary across the world. In the late 1970s, the Alvarezes and colleagues reported that it contained an abnormally high concentration of
iridium. In this layer, iridium levels reached 6 parts per billion by weight or more compared to 0.4 for the Earth's crust as a whole; in comparison, meteorites can contain around 470 parts per billion of this element. It was hypothesised that the iridium was spread into the atmosphere when the impactor was vaporized and settled across the Earth's surface amongst other material thrown up by the impact, producing the layer of iridium-enriched clay.
Multiple impact theory
In recent years, several other craters of around the same age as Chicxulub have been discovered, all between latitudes 20°N and 70°N. Examples include the
Silverpit crater in the
North Sea and the
Boltysh crater in
Ukraine. Both are much smaller than Chicxulub, but likely to have been caused by objects many tens of metres across striking the Earth. This has led to the hypothesis that the Chicxulub impact may have been only one of several impacts that happened nearly at the same time.
The collision of
Comet Shoemaker-Levy 9 with Jupiter in 1994 demonstrated that gravitational interactions can fragment a comet, giving rise to many impacts over a period of a few days if the comet should collide with a planet. Comets frequently undergo gravitational interactions with the
gas giants, and similar disruptions and collisions are very likely to have occurred in the past. This scenario may have occurred on Earth 65 million years ago.
In late 2006, Ken MacLeod, a
geology professor from the
University of Missouri–Columbia, completed an analysis of
sediment below the ocean's surface, bolstering the single-impact theory. MacLeod conducted his analysis approximately 4,500 kilometers (2,800 mi) from the Chicxulub Crater to control for possible changes in soil composition at the impact site, while still close enough to be affected by the impact. The analysis revealed there was only one layer of impact debris in the sediment, which indicated there was only one impact. Multiple-impact proponents such as
Gerta Keller regard the results as "rather hyper-inflated" and don't agree with the conclusion of MacLeod's analysis.
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