Perhaps every planet in the solar system is under constant fire from small space travelers, the surfaces of the planets are continuously bombarded by meteorites - small bodies of the solar system.
Sometimes even larger space catastrophes occur - collisions with asteroids, or, in other words, small planets, the diameter of which is from 1 to 1000 km, and the mass is less than one seven hundredth of the Earth's mass. An entire belt of asteroids now revolves around the Sun in an orbit located between the orbits of Mars and Jupiter.
What do these uninvited space guests bring to the planets? To find out, it will be enough to take a closer look at the surfaces of our planet's closest neighbors, and above all at its satellite, the Moon. Telescopes and satellite images show that all surfaces of neighboring planets are covered with a huge number of impact craters. These formations are bowl-shaped depressions in the ground, framed by an annular bulk shaft, while the inner slope of the shaft is steeper than the outer one.
The sizes of the craters are quite varied: from a few meters to thousands of kilometers across. It should be noted that there is an elevation in the center of the flat bottoms of large craters. Now it is absolutely certain that craters are the most common form of relief on the Moon, Mercury, Mars. So, the surfaces of all nearby planets are “decorated” with numerous “star wounds” (astroblemes) - traces of the encounters of these planets with small cosmic bodies.
And of course, meteorites have been brought to the Earth many times.
• The earliest mention of a meteorite fall that has survived to this day dates back to 644 BC. e. One of the oldest known meteorites is Mount Huangshitai, which is a huge two-ton boulder. It is located in the city of Xian (China), the meteorite took its place about 2 billion years ago.
• 1920 - on the territory of Namibia, the largest known meteorite was discovered - the Goba meteorite, which fell in prehistoric times, it weighs about 66 tons. This iron giant greatly outnumbers all the other space travelers recorded today.
• The second largest iron meteorite was discovered in the Gobi Desert. The forty-ton colossus landed there over a thousand years ago. In 1987, Chinese scientists sent her to Canton.
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• In third place in this row is the 15-ton celestial guest that fell in 1963 in Greenland.
• The fourth place belongs to the Australian 10-ton meteorite that fell to Earth in 1966.
• The largest stone meteorite fell on Chinese soil on March 8, 1976. They called the Jilin meteorite, its total mass is 4 tons (The weight of the largest meteorite fragment is 1770 kg).
• The heaviest meteorite of mixed composition, made of iron and stone, was discovered in Germany in 1805, weighing 1.5 tons.
• 1937 - another almost the same space visitor with a mass of 1.4 tons fell to the ground of Australia.
• Researchers believe that a huge number of meteorites are hidden under the ice sheet of Antarctica. It is believed that there are about 700,000 copies. Here, at the beginning of 1984, fragments of the oldest meteorite were found at the moment: scientists say that the meteorite fell to Earth about 4.6 billion years ago.
• 1833, on the night of November 12-13, a real meteor shower passed over the surface of our planet. It lasted 10 hours, during this time interval about 240,000 meteorites of various sizes fell to the ground, as they say “from small to large”.
• 1976, March 8 - a fleeting but rather abundant meteor shower was observed over northeastern China. It poured 37 minutes over an area of 500 square meters. After him, about a hundred "hailstones" of unearthly origin were found, among them was the famous Jilin.
Canadian scientists from the Ottawa Astrophysical Institute believe that over the years, a stream of meteorites with a total mass of about 21 tons falls on our planet.
Now, perhaps, it makes sense to return to the past of the Earth, because collisions with meteorites that occurred thousands, millions of years ago, not only left crater trails on the earth's surface, but also often became the cause of serious earthly disasters, which probably globally changed the Earth's biosphere.
Now about 100 shock geological structures have been discovered on the Earth's surface: 30 - in Europe, 26 - in North America, 18 - in Africa, 14 - in Asia, 9 - in Australia, etc. Of course, this is not enough, but it should be noted that the geological life of our planet is proceeding violently, and the external appearance of the Earth may well change; in a hundred million years, space “pockmarks” - traces of large meteorites falling, can disappear without a trace.
• Popigai Basin is the largest meteorite crater of those whose cosmic origin is not in doubt today. It is located in the valley of the right tributary of the Khatanga - the Popigai River, this is the northern part of the Siberian platform.
The inner crater has a diameter of 75 km, the outer one - 100 km. It is believed that the meteorite fell to Earth 30 million years ago. A large space body, flying at great speed, pierced the 1200-meter stratum of sedimentary rocks, but was stopped by the hard rocks of the Siberian platform foundation. The energy of the explosion that arose as a result of this catastrophe reached 10 to 23 Joules, that is, a thousand times more than the energy of a strong volcanic explosion. This colossal explosion produced the minerals found in the crater today.
The same minerals were obtained under laboratory conditions at shock pressures of one million bar and temperatures of about 1000 degrees. This means that just such conditions were formed at the epicenter of the explosion. It is not surprising that the rocks melted and lava flows with a high silica content appeared, which absolutely did not correspond to the composition of the basaltic magmatic eruptions of the Siberian platform that emerged from the bowels of the earth in this place. Another additional characteristic of this explosion may be the scattering of large blocks of crystalline rocks, torn out from the platform basement by the explosion and scattered by it 40 km from the outer edge of the Popigai depression.
• Another rather large meteorite crater was detected by geological surveys and drilling operations - this is the Puchezh-Katunskaya depression, located not far from Nizhny Novgorod, its diameter is approximately 100 km.
• The 50 km long Kara crater is located on the Pai-Khoi ridge, its hollow is filled with debris from the explosion, some of these debris are melted and turned into a vitreous substance.
• Finnish geologist P. Eskola in 1920 found a lava influx near Lake Yanisjärvi, located to the north of Lake Ladoga. The composition of this influx was close to the composition of the lava formations of meteorite craters. In addition, there are two rocky lava islands in the center of the lake. All this testifies to the fact that Lake Yanisjärvi is an ancient meteorite crater, its size is 14 by 26 km.
• More than 10 million years ago, a meteorite fell on Ukraine, leaving behind a huge dent with a diameter of 25 km - Boltyshsky crater.
• More than one million years ago, a crater with a diameter of about 20 km was formed in Karelia. This is the oldest meteorite trail in Russia.
• Not far from Kaluga, a 15 km explosive crater was discovered, the approximate age of which is 250 million years.
• The German city of Nordlingen was built inside the Reese meteorite crater. A huge meteorite fell to the Earth 15 million years ago as a result of the impact and explosion, a giant pit with a transverse size of about 20 km appeared. The study of this area showed that under the 35-meter layer of lake sediments there is an internal underground basin, which is about 700 meters deep and about 10 km in diameter.
This crater is littered with pieces of crushed, sintered, and in places molten rock. Since the soil that filled the crater is looser than the rocks surrounding the depression, the gravity indices are underestimated in place of the depression. Experts calculated that this kind of drop in gravity is due to a lack of mass in the crater area of 30-60 billion tons, which means that the explosion crushed and threw out 20 square kilometers of rock.
• The French crater Rochechouart, 15 km in diameter, appeared on the surface of our planet about 150-170 million years ago.
• At the end of the 19th century, in the state of Arizona (America), a deep study of the Diablo Canyon was begun - a crater with a diameter of 1.2 km and a depth of 170 meters, the basin is surrounded by a rampart up to 50 meters high. Local Indians have an interesting legend about this crater. According to her, the hollow was formed when God landed there on his fiery chariot, who flew from heaven. This legend confirms the meteorite origin of the crater. As a result of a detailed survey of this area within a radius of 10 km from the crater, fragments of an iron meteorite were found, their weight reached 20 tons.
Obviously, all this is only a small part of a huge meteorite, the fall of which was once observed by the ancient inhabitants of America. The main part of the meteorite was not found. Presumably, in general, it was an iron-nickel bar weighing about 5 million tons. This same funnel appeared as a result of the impact on the Earth of a fragment of a giant meteorite with a diameter of about 30 meters and weighing about 63,000 tons. Calculations showed that this impact released energy equal to the explosion energy of 3.5 million tons of TNT.
• The island of Saaremaa is located in the Baltic Sea, on its surface there is a whole group of ring-shaped dents of meteorite origin. The largest depression has a diameter of 110 meters, it is bordered by a shaft 6–7 meters high, formed from turned out dolomite layers. The other six depressions, surrounding the main one, have a transverse size of 16 to 20 meters. They are scattered over an area of 0.25 square kilometers.
• A granite dome with a diameter of about 40 km, surrounded by a 16 km strip of ancient sedimentary rocks, is the unique Vredefort ring found in South Africa. Such a mark on the Earth could have been left by a meteorite with a diameter of 2.3 km, weighing 30 billion tons, flying at a speed of 20 km / sec. The energy of the explosion was 50 times greater than the energy of the strongest earthquakes.
• Gosses Bluff is an Australian astrobleme, about 130 million years old. It looks like a hill, bordered by a ring of crushed rocks with a diameter of 14 km. The study of the structure of the earth's crust in this area was carried out using the most modern methods of seismic exploration, drilling deep wells, and also using blasting operations.
As a result, it was found that the underground relief of the crater is a hemispherical bowl with a radius of 2.3 km, which is surrounded by a smaller, saucer-shaped dent with a radius of about 11 km. In addition, there were discovered impakites - rocks consisting of dense bubble glass and formed by the impact and explosion of a meteorite. Based on all the data obtained, it was calculated that during the impact of the Gosses Bluff meteorite on our planet, an energy of 10 to 20 Joules was released.
• In South Texas, there is a hollow, framed by a ring of rocks, inside a huge dent, almost in the very center, a limestone dome rises 450 meters among horizontally lying rocks. The layers of soil there are broken, limestone covers a whole network of cracks - all this is the result of a powerful shock wave. American geologist A. Kelly believes that this astroblem appeared as a result of the fall of a comet into an ancient ocean 2-3 km deep. When the comet's nucleus touched the earth's crust, a monstrous explosion occurred. But the shock wave generated as a result of this did not cause serious damage around the epicenter, as it was greatly weakened by ocean waters.
A giant water funnel appeared, which lifted the bottom sediments, and then laid them down again, giving the shape of an annular shaft. In the center of the funnel, the water column disappeared and ceased to exert strong pressure on the seabed, which led to the heaving of the bottom surface. When the water whirlwind subsided, the turbid material settled to the bottom again, smoothing out the newly formed irregularities of the underwater relief. Tens of millions of years passed, and the crater appeared on the surface, then time and atmospheric phenomena took care of its destruction.
In 1958-1960 in Antarctica, on Wilkins' Land, two research expeditions worked: the French and the American. Scientists from both countries noted that there are strange deviations in gravity measurements in the area. When scientists tried to jointly find a solution, combining the results, it turned out that the area of the anomaly has the shape of a circle with a diameter of 240 km. At the same time, everything showed that it was a meteorite crater, since approximately the same deviations in gravity values are observed in other meteorite tracks.
This anomaly is a consequence of the formation of a depression, as well as loosening of rocks as a result of a meteorite explosion. The discovery of this crater helped to shed light on the origin of the dark green glassy stones - tektites. American scientist W. Burns argued that tektites are formed by melting from rocks during the impact of large meteorites on the Earth, the explosion scatters them over vast territories.
There was only one weak point in his theory: it remained unexplained that a large number of these stones were found in Australia and Tasmania, and there were no young meteorite craters. Now everything was falling into place: the meteorite crater discovered in Antarctica is located in the center of the Australian-Tasmanian arc.
Double Lake Clearwater (Canada) also has a meteoric origin. Both East Clearwater with a diameter of about 28 km, and Western - with a diameter of about 32 km - these are traces of impacts of two meteorites. The largest astroblem in Canada is the Manikugan-Mushalagan ring with a diameter of about 65 km.
The formation of the world's largest Canadian nickel deposit, Sudbury, is also likely to be related to the meteorite impact. The Sudbury ore basin is oval in shape and measures 60 km by 27 km. Quartz crystals were found there with a special orientation of cracks, such "notches" can appear on quartz during a nuclear explosion or when exposed to very high pressure, the same phenomenon is observed when a huge meteorite hits the ground and explodes.
In addition, one of the layers that make up the deposit, overlying the ore-bearing rocks - opaning tuff - is a crushed and newly cemented rock, which is fragments of bedrock granite and glass from molten and rapidly cooled minerals.
By their nature of formation, the Opaning is similar to the breeds found in other famous astroblems. Thus, it is possible to assume that during the fall of a giant meteorite, an intensification of volcanic activity took place and deep molten rocks saturated with metals took a new position close to the earth's surface. This is probably how this rich nickel deposit appeared.
In ancient times, there were incredibly heavy and extensive meteor showers more than once. Aerial photography over North and South Carolina revealed a large number of round and elliptical craters. Only large craters were counted about 140,000, and 100 of them are more than 1.5 km in diameter, the number of small ones is colossal: experts believe that there are more than half a million of them.
The meteorites are scattered over an area of 200,000 square kilometers, and the area of rockfall tracks is arched, in the center of the arc is the coastal city of Charlton, so that most of the meteorites fell into the Atlantic. It is believed that this stone rain was the result of the destruction of the largest asteroid in the atmosphere - its numerous debris dotted the coastal arc with a radius of more than 1000 km. It is believed that an asteroid weighing 1000-2000 billion tons, with a diameter of about 10 km, overheated, exploded in the atmosphere. Some other researchers believe that this meteor shower is of cometary origin.
P. Denisova