Our solar system is a very dynamic body which is constantly evolving and expanding. Two recent theories, the Nice Model and the Grand Tack, suggest that the gas giants moved around before settling into their modern orbits. This movement could have sent asteroids from the main belt raining down on the terrestrial planets, emptying and refilling the original belt. Asteroids hit usually results in global disaster, very dangerous asteroid impacts are rare. Researchers have estimated that such an impact would raise enough dust into the atmosphere to effectively create a “nuclear winter”, severely disrupting agriculture around the world. Asteroids that large strike Earth only once every 1,000 centuries on average. Smaller asteroids that are believed to strike Earth every 1,000 to 10,000 years could destroy a city or cause devastating tsunamis. Space rocks smaller than 82 feet (25m) will most likely burn up as they enter Earth’s atmosphere, which means that even if 2015 TC25 hit Earth, it probably wouldn’t make it to the ground. Here are the 10 major impacts of asteroid hits till date:
2 billion years ago Vredefort Crater hit Free State, South Africa. Also known as Vredefort Dome has an estimated radius of 118 miles. This is the largest impact structure ever recorded. Vredefort Crater was declared a UNESCO World Heritage Site in 2005. First, it was thought that dome was formed by volcanic explosion, but in the mid-1990s, evidence revealed it was the site of a huge bolide impact, as telltale shatter cones were discovered in the bed of the nearby Vaal River. Immediately after impact, the cater widened and shallowed as the rock below started to rebound and the walls collapsed. The world’s oldest and largest known impact structure was formed. The collapse was about 180-300 km wide. The uplift at the centre of the impact was so strong that a 25-km section of Earth’s crust was turned on end.
Sudbury basin hit Ontario, Canada 1.8 billion years ago and is still considered one of the most dreadful asteroids ever recorded. Estimated diameter of the asteroid on earth is 81 miles. Debris from the impact was scattered over an area of 1,600,000 square km thrown more than 800 km, rock fragments ejected by the impact have been found as far away as Minnesota. The deformation of the Sudbury structure occurred in five main deformation events (by age in Mega Years), first, formation of the Sudbury Igneous Complex (1849 ma). Second, Penokean Orogeny (1890-1830 ma), third, Mazatal orogeny (1700-1600 ma) and fourth, Lake Wanapitei (37 ma). This incident resulted in increased mineral content the soil of the area, making it well suited for agriculture, with numerous farms of vegetables, berry and dairy.
580 million years ago Acraman Cater had hit South Australia with estimated diameter of 56 miles. Some of the left overs of the impact include cones and shocked quartz in shattered bedrock on islands within Lake Acraman. Huge ejecta layer is believed to be a result of Acraman Cate, found within Edicaran rocks of the Flinders Ranges at least 3000 km east of the crater, and in drill holes from the officer Basin to the north. At the time these areas were shallow seas, and the ejecta settled into mud on the floor. It contains shocked minerals and small shatter cones, composed of similar in age and composition to that of the crater and is associated with an iridium anomaly suggesting contamination with extraterrestrial material. The asteroid was name after Acraman River which in turn was named after John Acraman, South Australian Colonial businessman.
Western Australia witnessed Woodleigh Crater approximately 364 million years ago. This crater is not exposed at the surface and has led to many discrepancies regarding its actual size. Reports on its diameter vary from 25-75 miles. Thin veins of melted glass, breccia and shocked quartz found would have formed under pressures 100,000 times greater than atmospheric pressure at sea level, or between 10 to 100 times greater than those generated by volcanic or earthquake activity. In 2018 of the extremely rare mineral reidite in a drillcore sample from the central uplift zone, supports the interpretation of the crater as being over 100 km in diameter and possibly the largest in Australia. Event occurred between the Late Triassic and Late Permian. Three of the largest impacts craters known in Australia are Woodleigh, Acraman and Tookoonooka. The Gnargoo structure, which has remarkable similarities to Woodleigh, is a nearby proposed impact crater on the Gascoyne platform.
Manicouagan Crater had hit Quebec Crater 215 million years ago. It is now Lake Manicouagan. Despite of erosion it is one of the most well-preserved craters on Earth with an estimated diameter of 62 miles the lake island in its centre is known as Rene-Levasseur Island, and its highest point is Mount Babel. The Lake and island are clearly seen from the space and are sometimes called the “eye of Quebec”. Mount Babel is interpreted as the central peak of the crater, formed by post-impact uplift. It has been suggested that the Manicouagan crater may have been part of a multiple impact event which also formed the Rochechouart crater in France, the Saint Martin crater in Manitoba, the Obolon’ crater in Ukraine, and the Red Wing Crater in North Dakota. The Manicouagan Reservoir is a part of hydro-Quebec, the provincial electrical utility.
145 years ago, North West, South Africa witnessed Morokweng Crater. Located near the Kalahari Desert in South Africa, this crater contained the fossilized remains of the meteorite that created it. Discovered in 1994, it is not exposed at the surface, but has been mapped by magnetic and gravimetric surveys. Core samples have shown it to have been formed by the impact of a chondrite asteroid estimated to have been 5 to 10 Km in diameter.
Impact dates back 70.3 million years, in Nenetsia, Russia. It lies in the southeastern end of the Yugorsky Peninsula, while the Ust-Kara site lies offshore, 15 km east of the small of the small Kara or Karskaya Guba inlet. It was formerly believed that these two sites were two separate craters and that they formed a twin impact structure from the Late Cretaceous. However, it seems that the Ust-Kara site does not exist as a separate site.
Yucatan Mexico was impacted by Chicxulub Crater approximately 65 million years ago. Many scientists believe that the meteorite that left this crater caused or contributed to the extinction of the dinosaurs. Estimates of its actual diameter range from 106 to a whooping 186 miles, which if proved right could mean it’s the biggest. It is the second largest confirmed impact structure on Earth, and the only one whose peak ring is intact and directly accessible for scientific research. The discoveries were widely seen as confirming current theories related to both the crater impact and its effects. A 2020 study concluded that the Chicxulub crater was formed by an inclined (45-60 degrees to horizontal) impact from the northeast.
Popigai Crater hit Siberia, Russia around 35.7 million years ago. Russian scientist claim that this crater site contains trillions of carats of diamonds, making it one of the largest diamond deposits in the world. These diamonds have been referred to as ‘impact diamonds.’ It is designated by UNESCO as a geopark, a site of special geological heritage. Its impact may have formed simultaneously with the approximately 35-million-year-old Chesapeake Bay and Toms Canyon. The shock pressure instantly transformed graphite in the ground into diamonds within a 13.6 Km radius of the impact point. These gems not only inherited tabular shapes of the original graphite grains but they additionally preserved the original crystals’ delicate striations.
10.Chesapeake Bay Centre
Discovered in early 1980s, Chesapeake Bay Centre had hit Virginia, United States approximately 35 million years ago. Located 125 miles away from Washington, D.C. it is one of the best-preserved “Wet-target” impact craters in the world. The continual slumping of the rubble within the crater has affected the flow of the rivers and shaped the Chesapeake Bay. The impact crater created a long-lasting topographic depression which helped predetermine the course of local rivers and the eventual location of the Chesapeake Bay. Most important for present day inhabitants of the area, the impact disrupted aquifers lie above a deep salty brine, remnants of 100- to 145-million-year-old early cretaceous North Atlantic seawater, making the entire lower Chesapeake Bay area susceptible to ground water contamination.