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According to the Planetary and Space Science Centre (PASSC) at the University of New Brunswick in Canada, there are 190 confirmed impact structures on Earth. Each is recorded in a database called the Earth Impact Database (EID). [1]
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According to the Planetary and Space Science Centre (PASSC) at the University of New Brunswick in Canada, there are 190 confirmed impact structures on Earth. Each is recorded in a database called the Earth Impact Database (EID). [1]
The following tables list geological features on Earth that are known impact events as well as possible, but for which there is currently no confirming scientific evidence in the peer-reviewed literature, impact events. In order for a structure to be confirmed as an impact crater, it must meet a stringent set of well-established criteria. Some proposed impact structures are likely to eventually be confirmed, whereas others are likely to be shown to have been misidentified (see below). Recent extensive surveys have been done for Australian (2005), [2] African (2014), [3] and South American (2015) [4] craters, as well as those in the Arab world (2016). [5] A book review by A. Crósta and U. Reimold disputes some of the evidence presented for several of the South American structures. [6]
Russia's Lake Cheko is thought by one research group to be the result of the famous Tunguska event, although sediments in the lake have been dated back more than 5,000 years. There is highly speculative conjecture about the supposed Sirente impact (c. 320 ± 90 AD) having caused the Roman emperor Constantine's vision at Milvian Bridge. [330] [ better source needed ]
The Burckle crater and Umm al Binni structure are proposed to be behind the floods that affected Sumerian civilization. [331] [332] The Kachchh impact may have been witnessed by the Harappan civilization and mentioned as a fireball in Sanskrit texts. [333]
Shortly after the Hiawatha Crater was discovered, researchers suggested that the impact could have occurred as late as ~12,800 years ago, leading some to associate it with the controversial Younger Dryas impact hypothesis (YDIH). [334] James Kennett, a leading advocate of the YDIH said, "I'd unequivocally predict that this crater is the same age as the Younger Dryas." [335]
These claims were criticised by other scholars. According to impact physicist Mark Boslough writing for Skeptical Inquirer the first reports of the impact released by science journalist Paul Voosen focused on this being a young crater which according to Boslough "set the tone for virtually all the media reporting to follow". Boslough argued, based on evidence and statistical probability, that once the crater has been drilled and researched "it will turn out to be much older." He complained that this important discovery "was tainted by connections to a widely discredited hypothesis and speculations that did not make it through peer review". [335] [336] The YDIH has since been refuted comprehensively by a team of earth scientists and impact experts. [337]
A 2022 study using Argon–Argon dating of shocked zircon crystals in impact melt rocks found outwash less than 10 km downstream of the glacier pushed the estimate back to around 57.99 ± 0.54 million years ago, during the late Paleocene. [338] [127] Confirmation would require drilling almost one km (3,300 ft) through the ice sheet above the crater to obtain a sample of dateable, solidified impact melt from the crater.
The age of the Bloody Creek crater [339] is uncertain.
As the trend in the Earth Impact Database for about 26 confirmed craters younger than a million years old shows that almost all are less than two km (1.2 mi) in diameter (except the three km (1.9 mi) Agoudal and four km (2.5 mi) Rio Cuarto), the suggestion that two large craters, Mahuika (20 km (12 mi)) and Burckle (30 km (19 mi)), formed only within the last few millennia has been met with skepticism. [340] [341] [342] However, the source of the young (less than a million years old) and enormous Australasian strewnfield (c. 790 ka) is suggested to be a crater about 100 km (62 mi) across somewhere in Indochina, [343] [344] with Hartung and Koeberl (1994) proposing the elongated 100 km × 35 km (62 mi × 22 mi) Tonlé Sap lake in Cambodia (visible in the map at the side) as a suspect structure. [345]
The Decorah crater has been conjectured as being part of the Ordovician meteor event. [346] [ better source needed ]
Several twin impacts have been proposed, such as the Rubielos de la Cérida and Azuara (30–40 Ma), [347] Cerro Jarau and Piratininga (c. 117 Ma), [73] and Warburton East and West (300–360 Ma). [348] However, adjacent craters may not necessarily have formed at the same time, as demonstrated by the case of the confirmed Clearwater East and West lakes.
Some confirmed impacts like Sudbury or Chicxulub are also sources of magnetic anomalies [349] and/or gravity anomalies. The magnetic anomalies Bangui and Jackpine Creek, [145] the gravity anomalies Wilkes Land crater and Falkland Islands, [350] and others have been considered as being of impact origin. Bangui apparently has been discredited, [25] [351] but appears again in a 2014 table of unconfirmed structures in Africa by Reimold and Koeberl. [3]
Several anomalies in Williston Basin were identified by Swatzky in the 1970s as astroblemes including Viewfield, Red Wing Creek, Eagle Butte, Dumas, and Hartney, of which only the last two are unconfirmed. [92]
The Eltanin impact has been confirmed (via an iridium anomaly and meteoritic material from ocean cores) but, as it fell into the Pacific Ocean, apparently no crater was formed. The age of Silverpit and the confirmed Boltysh crater (65.17 ± 0.64 Ma), as well as their latitude, has led to the speculative hypothesis that there may have been several impacts during the KT boundary. [352] [353] Of the five oceans in descending order by area, namely the Pacific, Atlantic, Indian, Antarctic, and Arctic, only the smallest (the Arctic) does not yet have a proposed unconfirmed impact crater.
Craters larger than 100 kilometres (62 mi) in the Phanerozoic (after 541 Ma) are notable for their size as well as for the possible coeval events associated with them especially the major extinction events.
For example, the Ishim impact structure [141] is conjectured to be bounded by the late Ordovician-early Silurian (c. 445 ± 5 Ma), [142] the two Warburton basins have been linked to the Late Devonian extinction (c. 360 Ma), [310] both Bedout and the Wilkes Land crater have been associated with the severe Permian–Triassic extinction event (c. 252 Ma), [354] [355] Manicouagan (c. 215 Ma) was once thought to be connected to the Triassic–Jurassic extinction event (c. 201 Ma) [356] but more recent dating has made it unlikely, while the consensus is the Chicxulub impact caused the one for Cretaceous–Paleogene (c. 66 Ma).
However, other extinction theories employ coeval periods of massive volcanism such as the Siberian Traps (Permian-Triassic) and Deccan Traps (Cretaceous-Paleogene).
There is geological evidence for impact events having taken place on Earth on certain specific occasions, which should have formed craters, but for which no impact craters have been found. In some cases this is because of erosion and Earth's crust having been recycled through plate tectonics, in others likely because exploration of the Earth's surface is incomplete, or because no actual crater was formed because the impacting object exploded as a cosmic air burst. Typically the ages are already known and the diameters can be estimated.
| Parent crater of | Expected crater diameter | Age | Notes |
|---|---|---|---|
| Pica glass | Unknown | 12 ka | [357] |
| Libyan desert glass | Unknown | 29 Ma | [358] [359] [360] [361] |
| Dakhleh glass | 0.4 km | 150 ka | [362] [363] |
| Argentinian impact glasses | Unknown | 6, 114, and 445 ka; 5.3 and 9.2 Ma | [364] [365] [366] |
| Australasian tektites | 32–114 km | 780 ka | [344] |
| Central American tektites | 14 km | 820 ka | [367] [368] [369] |
| Skye ejecta deposits | Unknown | 60 Ma | [370] |
| Stac Fada Member | 40 km | 1.2 Ga | [371] [372] [373] |
| Barberton Greenstone Belt spherules | 500 km | 3.2 Ga | [374] [375] |
| Marble Bar impact spherules | "hundreds of kilometers" | 3.4 Ga | [376] |
| Kaveri Crater | 120 km | 800 to 550 million years ago | [377] |
Some geological processes can result in circular or near-circular features that may be mistaken for impact craters. Some examples are calderas, maars, sinkholes, glacial cirques, igneous intrusions, ring dikes, salt domes, geologic domes, ventifacts, tuff rings, forest rings , and others. Conversely, an impact crater may originally be thought as one of these geological features, like Meteor Crater (as a maar) or Upheaval Dome (as a salt dome).
The presence of shock metamorphism and shatter cones are important criteria in favor of an impact interpretation, though massive landslides (such as the Köfels landslide of 7800 BC which was once thought to be impact-related) may produce shock-like fused rocks called "frictionite". [378]
An impact event is a collision between astronomical objects causing measurable effects. Impact events have been found to regularly occur in planetary systems, though the most frequent involve asteroids, comets or meteoroids and have minimal effect. When large objects impact terrestrial planets such as the Earth, there can be significant physical and biospheric consequences, as the impacting body is usually traveling at several kilometres a second, though atmospheres mitigate many surface impacts through atmospheric entry. Impact craters and structures are dominant landforms on many of the Solar System's solid objects and present the strongest empirical evidence for their frequency and scale.
A Martian meteorite is a rock that formed on Mars, was ejected from the planet by an impact event, and traversed interplanetary space before landing on Earth as a meteorite. As of September 2020, 277 meteorites had been classified as Martian, less than half a percent of the 72,000 meteorites that have been classified. The largest complete, uncut Martian meteorite, Taoudenni 002, was recovered in Mali in early 2021. It weighs 14.5 kilograms and is on display at the Maine Mineral and Gem Museum.
Tektites are gravel-sized bodies composed of black, green, brown or grey natural glass formed from terrestrial debris ejected during meteorite impacts. The term was coined by Austrian geologist Franz Eduard Suess (1867–1941), son of Eduard Suess. They generally range in size from millimetres to centimetres. Millimetre-scale tektites are known as microtektites.
Aorounga is an eroded meteorite impact crater in Chad, Africa. The exposed remnant of the crater is 12.6 km (7.8 mi) in diameter and its age is estimated to be less than 345 million years.
Gweni-Fada is a meteorite crater in the Ennedi Plateau, Chad.
The Popigai impact structure is the eroded remnant of an impact crater in northern Siberia, Russia. It is tied with the Manicouagan structure as the fourth largest verified impact structure on Earth. A large bolide impact created the 100-kilometre (62 mi) diameter crater approximately 35 million years ago during the late Eocene epoch. It might be linked to the Eocene–Oligocene extinction event.
Rochechouart impact structure or Rochechouart astrobleme is an impact structure in France. Erosion has over the millions of years mostly destroyed its impact crater, the initial surface expression of the asteroid impact leaving highly deformed bedrock and fragments of the crater's floor as evidence of it.
Roter Kamm is a meteorite crater, located in the Sperrgebiet, within the Namibian section of the Namib Desert, approximately 80 kilometres (50 mi) north of Oranjemund and 12 kilometres (7.5 mi) southwest of Aurus Mountain in the ǁKaras Region. The crater is 2.5 kilometres (1.6 mi) in diameter and is 130 metres (430 ft) deep. The age is estimated at 4.81 ± 0.5 Ma, placing it in the Pliocene. The crater is exposed at the surface, but its original floor is covered by sand deposits at least 100 metres (330 ft) thick.
The Vredefort impact structure is the largest verified impact structure on Earth. The crater, which has since been eroded away, has been estimated at 170–300 kilometres (110–190 mi) across when it was formed. The remaining structure, comprising the deformed underlying bedrock, is located in present-day Free State province of South Africa. It is named after the town of Vredefort, which is near its centre. The structure's central uplift is known as the Vredefort Dome. The impact structure was formed during the Paleoproterozoic Era, 2.023 billion years ago. It is the second-oldest known impact structure on Earth, after Yarrabubba.
Woodleigh is a large meteorite impact structure (astrobleme) in Western Australia, centred on Woodleigh Station east of Shark Bay, Gascoyne region. A team of four scientists at the Geological Survey of Western Australia and the Australian National University, led by Arthur J. Mory, announced the discovery in the 15 April 2000 issue of Earth and Planetary Science Letters.
HED meteorites are a clan (subgroup) of achondrite meteorites. HED stands for "howardite–eucrite–diogenite". These achondrites came from a differentiated parent body and experienced extensive igneous processing not much different from the magmatic rocks found on Earth and for this reason they closely resemble terrestrial igneous rocks.
Libyan desert glass or Great Sand Sea glass is an impactite, made mostly of lechatelierite, found in areas in the eastern Sahara, in the deserts of eastern Libya and western Egypt. Fragments of desert glass can be found over areas of tens of square kilometers.
Serra da Cangalha is an impact crater in the State of Tocantins, near the border of Maranhão State, in north/northeastern Brazil. The crater is between 12 and 13 kilometres in diameter, making it the second-largest known crater in Brazil. Its age is estimated to be about 220 million years. The name means Pack-Saddle Mountains in Portuguese.
The Santa Fe impact structure is an eroded remnant of a bolide impact crater in the Sangre de Cristo Mountains northeast of Santa Fe, New Mexico. The discovery was made in 2005 by a geologist who noticed shatter cones in the rocks in a decades-old road cut on New Mexico State Road 475 between Santa Fe and Hyde Memorial State Park. Shatter cones are a definitive indicator that the rocks had been exposed to a shock of pressures only possible in a meteor impact or a nuclear explosion.
Ramgarh crater, also known as Ramgarh structure, Ramgarh Dome and Ramgarh astrobleme, is a meteor impact crater of 3.5 kilometres (2.2 mi) diameter in Kota plateau of Vindhya Range located adjacent to Ramgarh village in Mangrol tehsil of Baran district in Rajasthan state of India. When formally accepted as the third crater in India, its diameter size would be between the two already confirmed craters in India - Dhala in Madhya Pradesh with 14 km diameter and Lonar in Buldhana district of Maharashtra with 1.8 km diameter.
Dhala crater is an impact structure formed by an asteroid impact. It is situated near Bhonti village in Pichhore block of Shivpuri district of Madhya Pradesh state in India. It is the largest impact structure in India, and between the Mediterranean and Southeast Asia. The diameter of the structure is estimated at 3 kilometres (1.9 mi), while other sources estimate its diameter to be 11 km diameter. It is the second such structure found in India, after Lonar lake.
The Late Heavy Bombardment (LHB), or lunar cataclysm, is a hypothesized astronomical event thought to have occurred approximately 4.1 to 3.8 billion years (Ga) ago, at a time corresponding to the Neohadean and Eoarchean eras on Earth. According to the hypothesis, during this interval, a disproportionately large number of asteroids and comets collided into the terrestrial planets and their natural satellites in the inner Solar System, including Mercury, Venus, Earth and Mars. These came from both post-accretion and planetary instability-driven populations of impactors. Although it gained widespread credence, definitive evidence remained elusive. However, recent re-appraisal of the cosmo-chemical constraints suggest there was no late spike in the bombardment rate.
As of June 2018, 12 confirmed impact structures have been found in Finland. They are listed below, sorted by original diameter.
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