Large bodies, larger than 100 m, easily pierce the atmosphere and reach the surface of our planet. At a speed of several tens of kilometers per second, the energy released during a collision significantly exceeds the energy of an explosion of an equal mass of TNT charge and is more comparable with nuclear weapons. In such collisions (scientists call them impact events), an impact crater, or astroblem, is formed.

Battle scars

Currently, more than one and a half hundred large astroblems have been found on Earth. However, almost until the middle of the 20th century, such an obvious reason for the appearance of craters as meteorite impacts was considered a very dubious hypothesis. Consciously search for large craters of meteorite origin began in the 1970s, they continue to be found even now - one or three annually. Moreover, such craters still form today, although the probability of their occurrence depends on the size (inversely proportional to the square of the crater diameter). Asteroids about a kilometer in diameter, which form 15-kilometer craters upon impact, fall quite often (by geological standards) - about once every quarter of a million years. But really serious impact events capable of forming a crater with a diameter of 200–300 km occur much less frequently, about once every 150 million years.

The largest is the Vredefort crater (South Africa). d = 300 km, age 2023 ± 4 Ma. The world's largest impact crater Vredefort is located in South Africa, 120 km from Johannesburg. Its diameter reaches 300 km, and therefore it is possible to observe the crater only on satellite images(as opposed to small craters that can be "covered" with a glance). Vredefort arose as a result of the collision of the Earth with a meteorite with a diameter of about 10 kilometers, and this happened 2023 ± 4 million years ago - thus, this is the second oldest known crater. Interestingly, the title of "largest" claims whole line unconfirmed "competitors". In particular, this is the Wilkes Land crater - a 500-kilometer geological formation in Antarctica, as well as the 600-km Shiva crater off the coast of India. In recent years, scientists have been inclined to believe that these are impact craters, although there is no direct evidence (for example, geological). Another contender is the Gulf of Mexico. There is a speculative version that this is a giant crater with a diameter of 2500 km.

Popular Geochemistry

How to distinguish an impact crater from other features of the relief? "Most main feature meteorite origin is that the crater is superimposed on geological relief randomly, - explains "PM" the head of the laboratory of meteoritics of the Institute of Geochemistry and analytical chemistry them. IN AND. Vernadsky (GEOKHI) RAS Mikhail Nazarov. “The volcanic origin of the crater must correspond to certain geological structures, and if there are none, but the crater is present, this is already a serious reason to consider the option of impact origin.”

The most inhabited is the crater Rees (Germany). d = 24 km, age 14.5 Ma. Nördlingen Rice is the name given to the region in Western Bavaria, formed by a meteorite fall more than 14 million years ago. Surprisingly, the crater is perfectly preserved and is observed from space - while it is clearly visible that a little away from its center in the impact recess stands ... a city. This is Nördlingen, a historic town surrounded by a fortress wall in the shape of an ideal circle - this is precisely due to the shape of the impact crater. Nördlingen is interesting to study on satellite photographs. By the way, Kaluga, also located in an impact crater formed 380 million years ago, can argue with Nördlingen in terms of “habitability”. Its center is located under the bridge across the Oka in the city center.

Another confirmation of the meteorite origin may be the presence in the crater of the actual meteorite fragments (impactor). This feature works for small craters (hundreds of meters in diameter - kilometers) formed by impacts of iron-nickel meteorites (small stone meteorites usually disintegrate when passing through the atmosphere). Impactors that form large (tens of kilometers or more) craters, as a rule, completely evaporate upon impact, so finding their fragments is problematic. But traces nevertheless remain: say, chemical analysis can detect an increased content of platinum group metals in the rocks at the bottom of the crater. The rocks themselves also change under the influence of high temperatures and the passage of the shock wave of the explosion: the minerals melt, enter into chemical reactions, rebuild crystal lattice- in general, a phenomenon occurs that is called impact metamorphism. The presence of resulting rocks- impactites - also serves as evidence of the impact origin of the crater. Typical impactites are diaplectic glasses formed at high pressures from quartz and feldspar. There are also exotic things - for example, diamonds were recently discovered in the Popigai crater, which were formed from graphite contained in rocks at high pressure created by shock wave.

The most obvious is the Barringer Crater (USA). d = 1.2 km, age - 50,000 years. Barringer Crater near the city of Winslow (Arizona) is apparently the most spectacular crater, since it was formed in a desert area and was practically not distorted by relief, vegetation, water, geological processes. The diameter of the crater is small (1.2 km), and the formation itself is relatively young, only 50 thousand years old, so its preservation is excellent. The crater is named after Daniel Barringer, a geologist who first suggested that it was an impact crater in 1902, and spent the next 27 years of his life drilling and searching for the meteorite itself. He did not find anything, went bankrupt and died in poverty, but the land with the crater remained with his family, which still profits from numerous tourists today.

The oldest one is the Suavyarvi crater (Russia). d = 16 km, age - 2.4 billion years. The oldest crater in the world, Suavyarvi, is located in Karelia, not far from Medvezhyegorsk. The diameter of the crater is 16 km, but its detection even on satellite maps extremely difficult due to geological deformations. It's no joke - the meteorite that created Suavjärvi hit the Earth 2.4 billion years ago! However, some do not agree with the Suavjärvi version. There is an opinion that the impact rocks found there were formed as a result of a series of small collisions much later. In addition, the Australian crater Yarrabubba, which could have formed 2.65 billion years ago, claims to be "ancient". And maybe later.

The most beautiful is the Kaali crater (Estonia). d = 110 m, age 4000 years. Beauty is a relative concept, but one of the most attractive and romantic craters for tourists is the Estonian Kaali on the island of Saaremaa. Like most impact craters of medium and small size, Kaali is a lake, and due to its relative youth (only 4000 years), it has retained an ideally correct rounded shape. The lake is surrounded by a 16-meter, again correct form earth rampart, nearby there are several smaller craters, “knocked out” by satellite fragments of the main meteorite (its mass ranged from 20 to 80 tons).

landscape design

When a large meteorite collides with the Earth, traces inevitably remain in the rocks surrounding the explosion site. impact loads- Concussion cones, traces of melting, cracks. An explosion usually forms breccias (rock fragments) - authigenic (simply crushed) or allogeneic (crushed, displaced and mixed) - which also serve as one of the signs of impact origin. True, the sign is not very accurate, since breccias can have various origins. For example, the breccias of the Kara structure long time considered deposits of glaciers, although later this idea had to be abandoned - for glacial they had too sharp corners.

Another outward sign meteorite crater are layers of underlying rocks squeezed out by the explosion (basement shaft) or ejected crushed rocks (bulk shaft). And in last case the order of occurrence of rocks does not correspond to the "natural". When falling large meteorites in the center of the crater, due to hydrodynamic processes, a hill or even an annular rise is formed - about the same as on the water, if someone throws a stone there.

The sands of Time

Not all meteorite craters are on the surface of the Earth. Erosion does its destructive work, and the craters are covered with sand and soil. “Sometimes they are found in the process of drilling, as happened with the buried Kaluga crater, a 15-km structure approximately 380 million years old,” says Mikhail Nazarov. “And sometimes interesting conclusions can be drawn even from their absence. If nothing happens to the surface, then the number of impact structures there should approximately correspond to the estimates medium density craters. And if we see deviations from the average value, this indicates that the area was subjected to some kind of geological process. And this is true not only for the Earth, but also for other bodies of the solar system. For example, the lunar seas bear significantly fewer traces of craters than the rest of the moon. This may indicate a rejuvenation of the surface - say, with the help of volcanism.

Mercury, Pluto, the Moon, Titan, other satellites and asteroids of the solar system - they are all full of craters, traces of large and not very collisions with meteorites and comets. Our Earth is well protected, in which most space invaders burn out before the surface - but large and fast ones break through, leaving indelible traces. Today we will look at the largest craters on Earth and restore those meteorites that managed to dig them.

Five Minute Theory

Before we find out where the most big crater on Earth, we need to understand the mechanism of their occurrence. After all, hundreds of years have passed since the fall of the big ones, and many craters are only now being discovered by the round outlines of the landscape from satellites or by analyzing the composition of minerals at the site of the fall. Look for craters also help folk tales- for example, the history of the Wolf Creek crater in Australia remained in the memory of the natives, although thousands of years had passed since the fall.

The main point - craters hundreds of times more meteorites who left them. It's all about the fall cosmic body at tremendous speed, it releases colossal energy - the most massive, dense and fastest meteorites that fell to Earth are hundreds of times more powerful than the most powerful nuclear bomb. The shock wave creates a pressure of millions of atmospheres, and the temperature at the epicenter of the contact is higher than - 15,000 ° C! From such heat, the rocks instantly evaporate and turn into plasma, which explodes and carries the remnants of the meteorite and destroyed rocks hundreds of kilometers away.

In the hot forge of the crater, molten rocks behave like liquids - a small hill forms in the center of the impact (like the one that rises on the water during the fall of the drop), and even if the meteorite hit under acute angle, the outline of the crater will be invariably round. And pressure gives rise to special rocks - impactites (from the English “impact” - imprint, blow). They are very dense, containing meteoric iron, iridium, and gold, and often take on crystalline and glassy forms. African impact diamonds, which can cut ordinary diamonds, are also the product of a giant meteorite impact.

In these footsteps, scientists are looking for craters. And when some are visible even to a non-specialist, others become sensations - people have been living in crater bowls for centuries and have no idea about it!

Acraman crater

The sixth largest crater in the world is hidden in southern Australia - formed 590 million years ago, it stretches 45 kilometers to the sides. At the time of the fall, the mess was a shallow, warm sea inhabited by primitive mollusks and arthropods - a meteorite impact scattered their remains with sedimentary rocks for hundreds of kilometers around. Over the years, the outlines of the crater have been smoothed out, but it is clearly visible on satellite images.

Now Arkaman does not look as menacing as his smaller brothers, but a significant part of it is occupied by the seasonal lake of the same name, which dries up in the heat. But 590 million years ago, a meteorite impact shook the entire planet. The diameter of the space traveler was 4 km, and it consisted of chondrite, a meteorite relative of terrestrial granite. Having hit the ground at a speed of 25 km / s, the Arkaman meteorite exploded with a force of 5200 gigatons, which is comparable only to the entire nuclear arsenal of the world. Thunder with a volume of 110 dB, causing pain in the ears and damaging hearing, came even 300 kilometers from the place of impact, and a squall of wind with a force of 357 m / s could even blow away skyscrapers!

The Manicouagan Crater in Quebec, Canada is one of the clearest and most beautiful giant craters on the planet. The distance from its centers to the outer edges is 50 kilometers, and inside the crater bowl, the annular lake Manicouagan has spilled, surrounding the central island. The asteroid that created the crater was 5 kilometers in circumference and crashed into prehistoric Canada 215 million years ago during the Triassic period. Since the impact yield of the Manicouagan meteorite was 7 teraton, it has long been considered as the cause mass extinction animals of that period.

And the Manicouagan crater has brothers all over the Earth - astronomers believe that a whole meteor Rain. Possible “one-year-olds” are Obolonsky crater in Ukraine, Red Wing in North Dakota and St. Martin’s crater in Matobe, Canada. They follow each other in a chain around the planet - perhaps they were born by the same huge one, split into pieces, or by a whole flock of them. However, it is not yet possible to determine this with certainty.

Popigai crater is the largest trace of a meteorite impact in the territory modern Russia located in northern Siberia. Its diameter is about 100 kilometers, and people even live in it - the village of Popigay, with a population of about 340 people, is located 30 kilometers from the center of the crater. Left such a large imprint 8-kilometer chondrite meteorite that fell on the territory of Eurasia 37 million years ago.

The impact of the asteroid gave the crater a special value - deposits of graphite under the surface turned into impact diamonds within a radius of 13.6 kilometers from the impact site. They are very small - up to 1 cm in diameter - and therefore not suitable for jewelry. But their unusual strength is very useful in industry and science, since “meteorite” diamonds are stronger than even the strongest synthetic ones. And in Popigay, as well as in the Manicouagan crater, there are also relatives, traces of a meteorite bombardment. It is believed that these meteorites led to global cooling, thanks to which large and complex mammals began to dominate - the ancestors of modern dogs, lions, elephants and horses.

Chicxulub crater

The trace of the impact is impressive - the diameter of the crater is 180 kilometers, it extends to land and sea, and maximum depth reaches 20 kilometers! The power of the meteorite explosion was 100 thousand megatons; "Tsar Bomba", the most powerful thermonuclear charge in the world, is able to give only a tenth of a percent of the total energy of the Chicxulub meteorite. From such a blow, fountains of lava rose on the far side of the Earth, 200 thousand cubic kilometers of rock were thrown into the air, and forests ignited from a hot wind.

Earthquakes, tsunamis, volcanic eruptions - the consequences of the impact that created the Chicxulub crater, changed the Earth's climate for a long time. By the way, the meteorite that did all this belongs to the Baptistina family of asteroids. This group often crosses the orbit of our planet - among other traces of the family, the Tycho crater is noted. These are all, of course, only theories: it is possible to accurately blame asteroids for the death of dinosaurs only when spacecraft bring samples of their soil.

An interesting fact is that the crater nature of the round Chicxulub basin was not discovered in scientific research. Symmetric rings on the continent and the ocean floor, as well as impact seals, were noticed by oil prospectors.

Sudbury Crater

Canada is definitely lucky in terms of craters - Sudbury, the second largest crater in the world with a girth of 250 kilometers, is located in the Canadian province of Ontario. The fall took place in the Paleoproteozoic era, 1.849 billion years ago - since then the outlines of the crater have smoothed out, and it began to resemble a huge valley 62 kilometers long, 30 kilometers wide and 15 kilometers deep. A worthy asteroid dug such a funnel - according to modern estimates, its radius was 7.5 kilometers.

The impact of the Sudbury meteorite hit right up to the mantle, and large pieces of rocks were found within a radius of 800 kilometers - in total, the fragments scattered over an area of ​​1,600,000 km2. But this big Bang enriched Canada. Hundreds of millions of years ago, the crater funnel was filled with magma rich in such heavy elements like gold, nickel, copper, palladium and platinum - and now the Sudbury basin belongs to the largest mining areas in the world. A rich mineral composition soil stimulates plant growth; only the cold climate hinders reaching agricultural heights.

The largest crater on Earth is the Vredefort crater in Republic of South Africa. Its diameter reaches 300 kilometers, and the size of the meteorite that created the crater is estimated at 20 kilometers. This is not only the largest, but also the second oldest crater - a meteorite explosion occurred 2.023 billion years ago. Only the Suavjärvi crater in Russia is older, 2.3 billion years old.

The Vredefort crater is so large that several dwarf European countries. It has several concentric rings, which are left only by exceptionally violent collisions, and are rarely preserved on Earth due to motion. tectonic plates and erosion. The favorable location helped Vredefort to survive - the central depression from the impact is especially clearly visible. As in other meteorite craters, valuable minerals can be found there, in particular gold. So far, however, the crater is dominated by farmers - the center of the community is the town of Vredefort, nestled in the center of the crater.

Theoretically, there are larger craters - under the ice of Antarctica, a 540-kilometer funnel is hidden from an asteroid impact; The Caribbean Sea and many other bodies of water could also have been created by meteorites. However, this will become known for sure only in the future, with the development of new technologies for scanning the depths of the soil and diving under water - for the most part, it was the miners and oil workers who discovered the craters of antiquity. So we will keep an eye on both miners and scientists.

Meteorites and asteroids are the heavy artillery of space. They plowed up, opened its crust to the very depths of the mantle, covered the surface with scatterings of craters. Our Earth, unlike an airless satellite, is protected from space rocks. In it, most of the "aliens" burn out before they touch the surface. But there are meteorites that break through the barrier and are capable of destroying entire cities and countries. Arizona Crater, also known as Barringer Crater and Devil's Canyon, reminds us of this - a trace from the closest meteorite fall to us.

How did the crater appear?

50 thousand years ago, the Arizona desert in the United States was not such a hot and dry place. Then it was a flowering field, crossed by forests and oak forests - the landscape was somewhat reminiscent of the forest-steppes of Ukraine and Russia. Mammoths and giant sloths roamed them, not much inferior in size to mammoths. The valley was cut by numerous rivers, and the rains were plentiful; nothing prevented the lush growth of vegetation. But one day the primitive idyll was interrupted.

The peaceful slumber was torn apart by a bright flash, and then a growing thunder - in the sky appeared fire ball which crashed down to Earth with lightning speed. A meteorite with a girth of 50 meters and a mass of 300 thousand tons cannot be called large - there are hundreds of times larger. Nevertheless, the explosion from the fall of the Arizona meteorite was colossal. The power was 150 megatons of TNT equivalent, which is three times more powerful than the most powerful detonated nuclear charge in history, the Tsar Bomba. This is not strange, because the fallen space rock belonged to the "heavy class" of meteorites containing a lot of nickel and iron.

The force of the impact of the meteorite devastated the surroundings. The 7-magnitude earthquake reached over 300 kilometers, and the sound of the explosion was as strong as the noise of an active construction site. A fireball with a radius of 700 meters rose above the horizon - its radiation set fire to grass and trees nearby. Rain from rubble and debris covered the area with a radius of 100 kilometers. And the meteorite itself half evaporated from the force of its own impact - and its fragments scattered around the crater and its environs.

Arizona Crater is visited by thousands of tourists, but they are not allowed to go down. On our site, with the help of Google StreetView, you can walk along the bottom of the crater like a real scientist!

Arizona meteorite crater today

However, time passed, and the Earth healed the wound on itself. Water and air smoothed out the outlines of the crater and transformed its appearance - it even managed to visit a lake into which nearby rivers flowed. The bottom was covered with sedimentary soil and seasonal vegetation, growing after rare desert rains, and the edges were smoothed. But the peculiarities of the desert climate of Arizona allowed the crater to be preserved better than many of its counterparts. Today we highlight:

• A funnel with a diameter of 1.2 kilometers and a depth of 170 meters. A small skyscraper will fit in it with a horse! In addition, the rim of the crater rises to a height of 46 meters.
• Unusual shape of the crater. Usually, impact marks are round or elliptical - and the Arizona crater, which was photographed from the air in the early 20th century, resembles a rounded square, like a chocolate bar. Scientists explain such anomalous outlines by shifts in the earth's crust caused by the impact force.

• The largest well-preserved crater on the planet. Yes, on Earth there are funnels from meteorites and more. The record holder, the Vredefort crater, stretches for 125 kilometers in all directions - several dwarf European countries would fit in its area. However, it is only possible to understand that Vredefort is a crater from a satellite. Water, wind and movement blurred the clarity of its shape. And the Arizona crater is not only intact, but also looks almost fresh, as if a meteorite fell recently.

Although the Indians have been collecting meteorite metal fragments for spears and arrows since ancient times, scientists have long thought that the Arizona crater was left from a volcano, and not from a cosmic body. However, the engineer Daniel Berringer, after whom the crater was named, thought otherwise. He believed that only a meteorite could dig such a huge bowl-shaped hole, and he hoped to find it under the crater and enrich himself. He bought the entire territory of the crater and searched for the remains for decades space iron. According to legend, he died of a heart attack when physicists calculated that there was nothing to look for underground.

However, now the crater brings his family a considerable income. Scientists are looking for minerals on the sacred bottom of the crater that can give them doctorates, tourists admire the majestic remains of a cosmic explosion from viewing platforms. In the United States, the Arizona crater is called the "Grave of Hats" - raging over the edges of the funnel strong wind, which blows the caps and hats of dozens of tourists into the inviolable bottom of the crater. And it was in the crater that the astronauts of the Apollo program worked out a mission to the moon. After all, this the only place on Earth, the landscape of which repeats the relief of our satellite.

Background

One of the first scientists to associate the crater with a meteorite fall was Daniel Barringer (1860-1929). He studied the impact crater in Arizona, which now bears his name. However, at the time, these ideas were not widely accepted (nor was the fact that the Earth is subject to regular meteor bombardment).

In the 1920s, the American geologist Walter Bacher, who studied a number of craters in the United States, suggested that they were caused by some kind of explosive events in the framework of his theory of "Earth pulsation".

Space research has shown that impact craters are the most common geological structure in the solar system. This confirmed the fact that the Earth is also subjected to regular meteorite bombardment.

File:Astrobleme.Morphology.1.jpg

Rice. 1. The structure of the astroblem.

Geological structure

The structural features of craters are determined by a number of factors, among which the main ones are the impact energy (depending, in turn, on the mass and speed of the cosmic body, the density of the atmosphere), the angle of contact with the surface and the hardness of the substances that form the meteorite and the surface.

During a tangential impact, furrow-like craters of small depth arise with weak destruction of the underlying rocks; such craters are quickly destroyed due to erosion. An example is the Rio Quarta crater field in Argentina, which is about 10,000 years old: the most large crater The field is 4.5 km long and 1.1 km wide with a depth of 7-8 m.

Rice. 2. Astrobleme Mjolnir (Norway, diameter 40 km), seismic data

When the direction of collision is close to vertical, rounded craters appear, the morphology of which depends on their diameter (see Fig. 1). Small craters (3-4 km in diameter have a simple cup-shaped shape, their funnel is surrounded by a rampart formed by uplifted layers of underlying rocks (Fig.1, 6) (basement rampart), covered by debris ejected from the crater (filled rampart, allogeneic breccia (Fig.1 : 1)).Under the bottom of the crater lie authigenic breccias (Fig.1: 3) - rocks crushed and partially metamorphosed (Fig.1: 4) during a collision, under the breccia there are fractured rocks (Fig. 1: 5,6) The depth-to-diameter ratio of such craters is close to 1/3, which distinguishes them from crater-like structures of volcanic origin, in which the depth-to-diameter ratio is ~0.4.

Rice. 3. Yalali astroblem (Australia, diameter 12 km), magnetic survey data

At large diameters, a central hill appears above the point of impact (in the place of maximum compression of the rocks), at even larger diameters of the crater (more than 14-15 km), ring uplifts are formed. These structures are associated with wave effects (like a drop falling on the surface of water). As the diameter increases, the craters rapidly flatten: the depth/diameter ratio drops to 0.05–0.02.

The size of the crater may depend on the softness of the surface rocks (the softer, the smaller the crater, as a rule).

On bodies that do not have dense atmosphere, long "rays" (formed as a result of the ejection of matter at the moment of impact) can persist around the craters.

According to international classification impactites (International Union of Geological Sciences, 1994), impactites localized in the crater and its environs are divided into three groups (according to composition, structure and degree of impact metamorphism):

• impacted rocks - target rocks that have been slightly transformed by a shock wave and, due to this, have retained their characteristic features;
• melt rocks - solidification products of the impact melt;
• impact breccias are clastic rocks formed without the participation of an impact melt or with a very small amount of it.

Impact events in Earth's history

It is estimated that 1-3 times in a million years a meteorite falls to the Earth, generating a crater at least 20 km wide. This suggests that fewer craters (including "young ones") have been found than they should be.

List of the most famous earth craters:

• Chesapeake Bay impact crater (US East)
• Haughton impact crater (Canada)
• Lonar crater (India)
• Mahuika crater (New Zealand)
• Manson crater (USA)
• Mistastin crater (Canada)
• Nordlinger Ries (Germany)
• panther mountain New York, (USA)
• Rochechouart crater (France)
• Sudbury Basin (Canada)
• Silverpit crater (UK, in the North Sea)
• Rio Cuarto craters (Argentina)
• The Siljan Ring (Sweden)
• Vredefort crater (Vredefort, South Africa)
• Weaubleau-Osceola impact structure (Central USA)

erosion of craters

Craters are gradually destroyed as a result of erosion and geological processes that change the surface. Erosion is most intense on planets with dense atmospheres. The well-preserved Arizona crater Barringer is no more than 50 thousand years old.

At the same time, there are bodies with very low cratering and, at the same time, almost devoid of atmosphere. For example, on Io, the surface is constantly changing due to volcanic eruptions, and on Europa, as a result of the reformation of the ice shell under the influence of inland ocean. In addition, the topography of craters on ice bodies is smoothed out as a result of ice melting (during geologically significant periods of time), since ice is more plastic than rocks. An example of an ancient crater with a worn relief is Valhalla on Callisto. Another one found on Callisto unusual view erosion - destruction presumably as a result of sublimation of ice under the influence of solar radiation.

The age of known terrestrial impact craters ranges from 1000 years to almost 2 billion years. Very few craters older than 200 million years have survived on Earth. Even less "survivable" are the craters located on the seabed.

Notes

Literature

• V. I. Feldman. Astroblems - stellar wounds of the Earth, Soros Educational Journal, No. 9, 1999
• Ring structures of the face of the planet. - M .: Knowledge, K 62 1989. - 48 s - (New in life, science, technology. Series "Earth Sciences"; No. 5)

Links

• Classification and nomenclature of impactites. International Union of Geological Sciences (IUGS), Subcommission of the Systematics of Metamorphic Rocks (SCMR), Study group K (Chairman: D. Stöffler)
• Detailed aeromagnetic survey over the Yallalie astrobleme, Western Australia by Phil Hawke & M. C. Dentith, Center for Global Metallogeny, The Univercity of Western Australia

Earth Craters Google Maps KMZ(KMZ label file for Google Earth)

Moon
Physical peculiarities	Internal structure Gravity Topography Magnetic field Atmosphere
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Lunar surface	Selenography Visible side The Other Side of the Sea impact crater

Thousands of years ago, some cosmic body fell to Earth, forming a gaping crater in the middle of the waterless Arizona desert.

Approximately 30,000-50,000 years ago, many centuries before the appearance of man, a giant stone block fell to Earth near the Devil's Canyon in Arizona, between the cities of Flagstaff and Winslow, and a bowl-shaped funnel 1250 m in diameter and 174 m deep was formed on the surface of the planet.

From the flat surface of the desert, the outer slopes of the 45 m high crater seem like a small hilly ridge, so the gaping depression hidden behind them was discovered by Europeans only in 1871. Initially believed that the crater of volcanic origin. But in 1890, iron fragments were found among the wreckage, and although the find was not given much importance at that moment, some scientists began to think that such an impressive mark on the face of the Earth could only be the result of the fall of an extraterrestrial body.

After exploring the area in 1902, Philadelphia mining engineer Daniel Barringer became so convinced of the existence of an iron-bearing meteorite that he purchased the area in 1906 and began drilling. At first, he assumed that, since the crater has an almost regular rounded shape, the body that created it should be buried in the center. Later, he discovered that if you fire a bullet into soft soil, even at an acute angle to the surface, the hole also turns out to be round.

This observation, as well as the fact that the southeastern wall of the crater is more than 30 m higher than the height of its other edges, led him to the idea that the meteorite fell from the north at an acute angle and, therefore, should be located with southeast side crater. This is where the drilling began. At a depth of 305 m, an increasing number of iron and iron-nickel fragments were found. At a depth of 420 m, the progress of the drill completely stopped - obviously, the drill reached the surface of a solid meteorite substance. In 1929, due to financial difficulties, drilling was stopped, but by that time it was already clear that the crater was indeed formed by a meteorite fall.

The dimensions of this cosmic body have become the subject of speculation. In the 30s, scientists estimated its weight at 14 million tons, and its diameter at 122 m. According to modern estimates, its weight reached 70,000 tons, and its diameter was 25-30 m.

But even assuming that the size of this space alien were not so great, its collision with our planet should have been in the nature of a cataclysm.

To form such huge crater, the meteorite was flying through the atmosphere at 69,000 km/h or so. The force of its impact on the Earth was equal to the force of an explosion of 500,000 tons of explosive (almost 40 times more powerful than an explosion atomic bomb that destroyed Hiroshima). 100 million tons of rocks crushed into dust were thrown into the atmosphere. The sediments were formed, which now make up the slopes of the crater.

Drops of molten metal from the meteorite scattered over an area of ​​260 km2. The fragments were no larger than pebbles, although some reached 630 kg. The rocks ejected from the crater were a mixture of sandstone and limestone - the remains of fossil-rich rocks from the bottom of a prehistoric lake that once existed in this region. A thick lens-shaped layer of the same rocks, called a breccia, now covers the crater floor.

In the 1930s, funds were allocated to drill through the breccia to the bottom of the crater. At a depth of up to 260 m, traces of nickel and iron appeared, below this level the rocks remained intact. It can be assumed that the remains of the meteorite lie under the southern edge of the crater, but make up no more than 10% of the main rocks. The main mass of the meteorite was dispersed during the collision, turning into iron-nickel fragments.

In 1960, traces of two rare forms silica - coesite and stishovite, which are also obtained artificially under conditions of high pressures and temperatures. (Although stishovite can form under high pressure in the depths earth's crust, but when it comes to the surface, it turns back into quartz.)

The presence of these minerals in natural form near the crater is indisputable evidence of a powerful collision. All doubts about the nature of the origin of the crater were dispelled, and Barringer's assumptions about the meteorite nature of the crater, which now bears his name, were fully confirmed.

outlandish light

"Shooting Stars" is one of the most fantastic celestial phenomena. But in fact, the light does not come from a star, a stone or metal fragment of a meteorite that flew from space into earth's atmosphere. The rushing fragment compresses the air in front of it with such force that it is white-hot, heating the outer layers of the meteorite, which begin to glow and finally melt. Burning gas and molten matter are ejected by the meteorite all the way down, causing a glow in the form of a fiery streak.

Thousands of such fragments enter the atmosphere every day, but they are often so small that they are difficult to see. Some - either because of their extreme size, or because high content metals in them - do not completely burn out during the fall. The huge meteorite that caused the formation of the Arizona crater must have been an enchanting sight when it fell.