From Wikipedia, the free encyclopedia
The Chicxulub crater ( ; Mayan: ) is an
buried underneath the
in . Its center is located near the town of , after which the crater is named. It was formed by a large
about 10 to 15 kilometres (6.2 to 9.3 miles) in diameter, the , striking the Earth. The date of the impact coincides precisely with the
(K–Pg boundary), slightly less than 66 million years ago, and a widely accepted theory is that worldwide
from the event was the cause of the , a
in which 75% of plant and animal species on Earth suddenly became extinct, including all non- . The crater is 150 kilometres (93 miles) in diameter and 20 km (12 mi) in depth, well into the
of the region of about 10–30 km (6.2–18.6 mi) depth. It makes the feature the second of the , and the only one whose peak ring is intact and directly accessible for scientific research.
The crater was discovered by Antonio Camargo and Glen Penfield,
who had been looking for
in the Yucatán during the late 1970s. Penfield was initially unable to obtain evidence that the geological feature was a crater and gave up his search. Later, through contact with Alan Hildebrand in 1990, Penfield obtained samples that suggested it was an impact feature. Evidence for the impact origin of the crater includes , a , and
in surrounding areas.
In 2016, a scientific drilling project drilled deep into the
of the impact crater, hundreds of meters below the current sea floor, to obtain
samples from the impact itself. The discoveries were widely seen as confirming current theories related to both the crater impact and its effects.
map of the Chicxulub impact structure. The coastline is shown as a white line. A striking series of
features reveals the location of the crater. White dots represent water-filled
(solution-collapse features common in the limestone rocks of the region) called cenotes after the Maya word dzonot. A dramatic ring of cenotes is associated with the largest peripheral gravity-gradient feature. The origin of the cenote ring remains uncertain, although the link to the underlying buried crater seems clear.
In 1978, geophysicists Glen Penfield and Antonio Camargo were working for the Mexican state-owned oil company , or Pemex, as part of an airborne magnetic survey of the
north of the Yucatán peninsula. Penfield's job was to use geophysical data to scout possible locations for oil drilling. In the data, Penfield found a huge underwater arc with "extraordinary symmetry" in a ring 70 km (40 mi) across. He then obtained a
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, the ends of which pointed northward. Comparing the two maps, he found the separate arcs formed a circle, 180 km (110 mi) wide, centered near the Yucatá 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
conference. That year's conference was underattended and their report attracted scant attention. Coincidentally, many experts in
were attending a separate conference on Earth impacts. Although Penfield had plenty of geophysical data sets, he had no rock cores or other physical evidence of an impact.
He knew Pemex had drilled exploratory wells in the region. In 1951, one bored into what was described as a thick layer of
about 1.3 kilometres (4,300 ft) down. This layer could have resulted from the intense heat and pressure of an Earth impact, but at the time of the borings it was dismissed as a —a feature uncharacteristic of the region's geology. Penfield tried to secure site samples, but was told such samples had been lost or destroyed. When attempts at returning to the drill sites and looking for rocks proved fruitless, Penfield abandoned his search, published his findings and returned to his Pemex work.
Penfield with the sample of
found at Well #2, Chicxulub
At the same time, in 1980, geologist
and his father, Nobel Prize-winning scientist , put forth
that a large extraterrestrial body had struck Earth. In 1981, unaware of Penfield's discovery,
graduate student Alan R. Hildebrand and faculty adviser William V. Boynton published a draft Earth-impact theory and sought a candidate crater. Their evidence included greenish-brown clay with surplus
containing
grains and small weathered
beads that looked to be . Thick, jumbled deposits of coarse rock fragments were also present, thought to have been scoured from one place and deposited elsewhere by a
resulting from an Earth impact. Such deposits occur in many locations but seem concentrated in the
basin at the K–Pg boundary. So when Haitian professor Florentine Morás discovered what he thought to be evidence of an ancient volcano on , Hildebrand suggested it could be a telltale feature of a nearby impact. Tests on samples retrieved from the K–Pg boundary revealed more tektite glass, formed only in the heat of asteroid impacts and high-yield .
reporter Carlos Byars told Hildebrand of Penfield's earlier discovery of a possible impact crater. Hildebrand contacted Penfield in April 1990 and the pair soon secured two drill samples from the Pemex wells, stored in . Hildebrand's team tested the samples, which clearly showed
materials.
A team of California researchers including , , and Charles Duller, surveying regional satellite images in 1996, found a
() ring centered on Chicxulub that matched the one P the cenotes were thought to be caused by
of -weakened
around the impact crater wall. More recent evidence suggests the actual crater is 300 km (190 mi) wide, and the 180 km ring is in fact an inner wall of it.
An animation showing the impact, and subsequent crater formation (University of Arizona, Space Imagery Center).
Researchers at the
dated tektites samples from the impact as 66,038,000 ± 11,000 years old.
had an estimated diameter of 15 kilometres (9.3 mi), and delivered an estimated energy of 10 billion
A-bombs (about
{\displaystyle 1\times 10^{23}}
, or 100,000 EJ). By contrast, the most powerful man-made explosive device ever detonated, the , had an energy of only 210
{\displaystyle 2.10\times 10^{17}}
joules, the yield of 50
of TNT). The object dug a hole 100 kilometres (62 mi) wide and 30 kilometres (19 mi) deep, leaving a crater mainly under the sea and covered by 600 metres (2,000 ft) of
in the 21st century.
The impact would have caused a
over 100 metres (330 ft) tall that would have reached all the way to what are now Texas and Florida. The height of the tsunami was limited by the relatively shallow sea in th in deep ocean it would have been 4.6 kilometres (2.9 mi) tall. A cloud of super-heated 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
upon re-entry, broiling the
and possibl meanwhile, colossal
would have triggered global
and . Fossil evidence for an instantaneous die-off of diverse animals was found in a soil layer only 10 centimetres (3.9 in) thick in
some 5,000 kilometres (3,100 mi) away from the impact site, indicating that death and burial under debris occurred suddenly and quickly over wide distances on land.
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. The shock production of
caused by the destruction of
rocks would have led to a sudden . Over a decade or longer, sunlight would have been blocked from reaching the surface of the Earth by the dust particles in the atmosphere, cooling the surface dramatically.
by plants would also have been interrupted, affecting the entire . A model of the event developed by Lomax et al. (2001) suggests that
(NPP) rates may have increased to higher than pre-impact levels over the long term because of the high carbon dioxide concentrations.
In February 2008, a team of researchers led by Sean Gulick at the 's
used seismic images of the crater to determine that the impactor landed in deeper water than was previously assumed. They argued that this would have resulted in increased sulfate aerosols in the atmosphere. According to the press release, that "could have made the impact deadlier in two ways: by altering climate (sulfate aerosols in the upper atmosphere can have a cooling effect) and by generating
(water vapor can help to flush the lower atmosphere of sulfate aerosols, causing acid rain)." This was borne out by the results of a drilling project in 2016 which found that sulfate containing rocks found in the area were not found in the peak ring (the rocks found were from deep within the earth's crust instead), the interpretation being that they had been vaporized by the impact and dispersed into the atmosphere.
A long-term local effect of the impact was the creation of the Yucatán sedimentary basin which "ultimately produced favorable conditions for human settlement in a region where surface water is scarce."
The piece of clay, held by Walter Alvarez, that sparked research into the impact theory. The greenish-brown band in the center is extremely rich in .
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
reaching to a depth of almost 1,000 m (3,300 ft). These rocks date back as far as the . Below these layers lie more than 500 m (1,600 ft) of
glass and . These andesitic
were only found within the supposed impact feature, as is . The K–Pg boundary inside the feature is depressed to 600 to 1,100 m (2,000 to 3,600 ft) compared with the normal depth of about 500 m (1,600 ft) measured 5 km (3 mi) away from the impact feature. Along the edge of the crater are clusters of
or sinkholes, which suggest that there was a water basin inside the feature during the
period, after the impact. The
of such a basin would have dissolved the
and created the caves and cenotes beneath the surface. The paper also noted that the crater seemed to be a good candidate source for the
reported at .
In September 2007, a report published in
proposed an origin for the asteroid that created the Chicxulub crater. The authors, , David Vokrouhlick?, and , argued that a collision in the asteroid belt 160 million years ago resulted in the
of asteroids, the largest surviving member of which is . They proposed that the "Chicxulub asteroid" was also a member of this group. The connection between Chicxulub and Baptistina is supported by the large amount of carbonaceous material present in microscopic fragments of the impactor, suggesting the impactor was a member of a rare class of asteroids called , like Baptistina. According to Bottke, the Chicxulub impactor was a fragment of a much larger parent body about 170 km (106 mi) across, with the other impacting body being around 60 km (37 mi) in diameter. In 2011, new data from the
revised the date of the collision which created the
to about 80 million years ago. This makes an asteroid from this family highly improbable to be the asteroid that created the Chicxulub crater, as typically the process of resonance and collision of an asteroid takes many tens of millions of years. In 2010, another hypothesis was offered which implicated the newly discovered asteroid , a member of the
of asteroids, as a possible remnant cohort of the K/Pg impactor.
The Chicxulub Crater lends support to the theory postulated by the late
and his son,
, that the extinction of numerous animal and plant groups, including non-avian , may have resulted from a
impact (the ). Luis and Walter Alvarez, at the time both faculty members at the , postulated that this enormous extinction event, which was roughly contemporaneous with the postulated date of formation for the Chicxulub crater, could have been caused by just such a large impact. The age of the rocks marked by the impact shows that this impact structure dates from roughly 66 million years ago, the end of the
, and the start of the
period. It coincides with the K–Pg boundary, the geological boundary between the Cretaceous and Paleogene. The impact associated with the crater is thus implicated in the , including the worldwide extinction of non-avian . This conclusion has been the source of controversy. In March 2010, forty-one experts from many countries reviewed the available evidence: 20 years' worth of data spanning a variety of fields. They concluded that the impact at Chicxulub triggered the
at the K–Pg boundary. In 2013 a study compared
from the Chicxulub impact with the same isotopes in ash from the boundary where t the study concluded that the impact glasses were dated at 66.038 ± 0.049 Ma, and the deposits immediately above the discontinuity in the geological and fossil record was dated to 66.019 ± 0.021 Ma, the two dates being within 19,000 years of each other, or almost exactly the same within experimental error. The theory is now widely accepted by the . Some critics, including
, argue that such an impact would have killed
as well as dinosaurs, yet the frogs survived the extinction event.
argues that recent core samples from Chicxulub prove the impact occurred about 300,000 years before the mass extinction, and thus could not have been the causal factor. However, this conclusion is unsupported by radioactive dating and sedimentology.
The main evidence of such an impact, besides the crater itself, is contained in a thin layer of clay present in the
across the world. In the late 1970s, the Alvarezes and colleagues reported that it contained an abnormally high concentration of . Iridium levels in this layer reached 6 parts per billion by weight or more compared to 0.4 for the Earth' in comparison, meteorites can contain around 470 parts per billion of this element. It was hypothesized 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. Similarly, an
in core samples from the
suggested the
of about 2.5 million years ago.
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 disputed
in . Both are much smaller than Chicxulub, but are likely to have been caused by objects many tens of meters 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. Another possible crater thought to have been formed at the same time is the larger , though the structure's status as an impact crater is contested.
The collision of
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 undergo gravitational interactions with the , and similar disruptions and collisions are very likely to have occurred in the past. This scenario may have occurred on Earth at the end of the Cretaceous, though Shiva and the Chicxulub craters might have been formed 300,000 years apart.
In late 2006, Ken MacLeod, a
professor from the , completed an analysis of
below the ocean's surface, bolstering the single-impact theory. MacLeod conducted his analysis approximately 4,500 kilometres (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
regard the results as "rather hyper-inflated" and do not agree with the conclusion of MacLeod's analysis, arguing that there might only be gaps of hours to days between impacts in a multiple-impact scenario (cf. Shoemaker-Levy 9) which would not leave a detectable gap in deposits.
Chicxulub is the only known Earth crater with a remaining impact , but it is under 600 m (2,000 ft) of sediment. During April and May 2016, a joint - Mission Specific Platform Expedition no. 364 obtained the first offshore
from the peak ring, the central zone of the crater. During Expedition 364, DES drillers on the L/B Myrtle collected core samples to enable
Science Party members to study how the peak ring formed and calculate the total impact energy.
Their target depth was 1,500 m (4,900 ft) below the bottom of the ocean, but they reached an acceptable 1,335 m. Sample preparation and analysis are being performed at Bremen, Germany.
It was announced in November 2016 that pink , usually found deep in the Earth's crust, had been found in drilling samples. It suggests the impact was so great it shocked and melted rocks found deep in the crust, causing them to shoot up before falling back down to produce the peak rings. The granite samples were also found to be lighter and weaker than normal granite, a result of the shock and extreme conditions of the impact. The findings confirmed that the rock comprising the peak ring had originated deep in the earth, and was ejected to the surface. It had been subjected to immense pressures and forces and had been melted by heat and shocked by pressure from its usual state into its present
the fact that the peak ring was made of granite was also significant, since granite is not a rock found in sea-floor deposits, originating much deeper in the earth, and had been ejected to the surface by the immense pressures of impact. , a -containing rock that is usually present in the shallow seabed of the region, had been almost entirely removed and likely vaporized to enter the atmosphere, an event immediately followed by a
sufficient to lay down the largest-known layered bed of sand, around 100 m deep and separated by grain size, directly above the peak ring. These types of sand deposits are caused by extreme water movement, where the larger and heavier sand grains settle first, followed by lighter and smaller grains.
Taken together, analyses indicate that the impactor was large enough to create a 120-mile peak ring, to melt, shock and eject granite from many miles within the earth, to create colossal water movements, and to eject an immense quantity of vaporized rock and sulfates into the atmosphere, where they would have persisted over years to decades. This global dispersal of dust and sulfates would have led to a sudden and catastrophic effect on the climate worldwide, large temperature drops, and devastated the . The researchers stated that the impact generated an environmental calamity that extinguished life, but it also induced a vast subsurface
that became an oasis for the recovery of .
A program on British television described that the drilling revealed, from top down: thick C a graded sediment deposit from one , over 100 the impact melted basement
from the Earth's
and . The peak ring itself did not contain the
that the rocks in the area around contain, leading the program makers to conclude that all the calcium sulphate in the crater area had been vaporized into the atmosphere and had become a dense
veil stopping the sunlight. As additional clues of the resulting megatsunami represented in a New Jersey quarry, a dense marine
was found on the Cretaceous–Paleogene boundary containing a mixture of dead sea animals with little or no damage from scavengers or predators. Also related to this tsunami was a dense dinosaur bone bed on the Cretaceous–Paleogene boundary found in .
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