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Meteorites are untamed, erratic, and ubiquitous. Our planet is etched with the marks of numerous collisions. Studying these craters provides fascinating glimpses into Earth's formation and hints at what the future might hold.
10. The Enormous Sea Scorpions Comparable to Humans
The prehistoric era was home to fearsome creatures, and in 2015, another was unearthed in the fossilized remains of a meteorite crater in Decorah, Iowa. Following a meteorite strike approximately 470 million years ago, the region was submerged under ocean water. This created a dense, brackish environment ideal for the human-sized sea scorpion, which scientists named Pentecopterus, inspired by an ancient Greek warship.
In 2010, when a nearby river was dammed, the crater was exposed, revealing a treasure trove of fossils. Researchers discovered numerous adult and juvenile specimens, some still displaying intricate skin patterns. Resembling creatures from a sci-fi film, adults grew up to 2 meters (6 ft) long and possessed powerful limbs designed for capturing and securing prey.
Certain fossils even preserved fine hairs covering their tough exoskeletons. These hairs likely enhanced the creature's ability to sense environmental changes and movement, as well as improve its agility in dark waters. Most importantly, they would have aided the scorpion in detecting nearby prey.
Their heavily armored bodies featured a large head shield, and their adaptations likely positioned them as the apex predators of their time. Thriving in the oxygen-depleted waters at the crater's base, they held a significant advantage in the struggle for survival.
This finding also extended the lineage of eurypterids, demonstrating their existence on Earth as far back as 467 million years ago, nearly nine million years earlier than previously believed. Adding to their eerie legacy, their modern-day relatives include ticks and spiders.
9. Reidite: The Super Diamond
The Rock Elm meteorite crater in western Wisconsin formed between 465–475 million years ago. A meteorite traveling at approximately 110,000 kilometers per hour (70,000 mph) struck the Earth, creating a crater roughly 6 kilometers (4 mi) wide and 300 meters (1,000 ft) deep. In 2014, the site revealed a surprising find: a rare mineral ranking among the hardest substances on Earth.
Reidite has only been discovered in three other meteorite craters globally, with the Rock Elm sample being the oldest. A variant of zircon, reidite was first identified in 1960 and has since been found in craters located in Virginia, Germany, and China.
The scientist who made the discovery noted that it was even rarer than a 4.4-billion-year-old zircon. This is unsurprising, given that the mineral traces are finer than a human hair. They can only be definitively identified under a microscope, which enables researchers to analyze how the sample reflects light.
Reidite forms under extreme pressure, similar to zircon and diamonds. While diamonds are created under Earth's natural pressure, reidite requires the immense force of a meteorite impact. The resulting mineral shares the same chemical makeup as zircon but is approximately 10 times denser.
8. Twin Meteorite Impacts
A single meteorite impact is catastrophic, but two simultaneously? Though rare and improbable, this occurred in Sweden.
Around 460 million years ago, two asteroids simultaneously struck what is now Jamtland. Researchers from the University of Gothenburg linked this event to a massive collision between two asteroids in the belt between Jupiter and Mars. The collision generated numerous fragments, which subsequently rained down on Earth and neighboring planets.
Samples from the craters confirm they formed at the exact same time, a rare coincidence. The unusual double-crater formation is asymmetrical, with diameters measuring approximately 8 kilometers (5 mi) and 700 meters (2,300 ft), respectively.
During that period, the impact site was entirely submerged. The force of the meteorites would have split the ocean, exposing the seabed for over 1.5 minutes before the waters surged back with a colossal wave, dramatically altering the planet's surface.
7. Quasicrystals
Crystals are created through a repetitive arrangement of atoms that interlock seamlessly. Naturally occurring crystals share similar molecular structures, such as six-sided atoms bonding together without leaving any gaps.
In 2015, scientists discovered something unprecedented in a 4.5-billion-year-old meteorite retrieved from a Russian crater. Dubbed a quasicrystal, this unique material consists of 10-sided atoms arranged in a tubular formation, unlike any terrestrial crystals.
The 10-sided structure forces these atoms to combine unevenly, creating a disordered arrangement compared to the orderly crystals found on Earth. The atoms in this quasicrystal rarely bond naturally, as aluminum typically binds with oxygen first, preventing it from linking with elements like iron and nickel, as observed here.
Only one other quasicrystal has been discovered, also from a Russian meteorite in 2009. That crystal featured five-sided atoms, another structure uncommon on Earth. The age of these meteorites suggests the crystals originated extraterrestrially, forming around the time of the universe's creation.
The implications are profound. These irregular crystals defy fundamental principles of crystal science. Researchers remain puzzled about their formation and whether such structures are common beyond our planet.
6. The Ancient Asteroid
When a meteorite strikes Earth, the immense force typically vaporizes it, leaving only fragments behind. This made the discovery of a fossilized meteorite in South Africa's Morokweng crater particularly surprising.
The meteorite fragment measured about 25 centimeters (10 in) across and was located 750 meters (2,500 ft) underground. While not the largest meteorite to hit Earth, it is the biggest intact piece discovered as of late 2015.
The crater, discovered in the 1990s, is believed to be around 145 million years old and spans approximately 70 kilometers (45 mi). It's astonishing that such a large portion of the meteorite remained intact, especially considering that smaller craters can generate temperatures up to 14,000 degrees Celsius (25,000 °F), which typically vaporize or fuse the meteorite into surrounding rock, leaving only tiny remnants for analysis.
Analysis revealed that this meteorite fragment contains a higher concentration of uranium compared to most other fragments. This makes it slightly more radioactive than typical meteorites. Additionally, it is significantly older than any substantial meteorite piece studied so far.
5. The Origins Of Life On Earth
Researchers from the University of Western Ontario examined rocks from Canada's Haughton Crater and discovered that the extreme pressure and temperatures during the impact altered the rocks, making them far more conducive to supporting early life.
The intense forces of an impact not only create microscopic pores within rocks, ideal for hosting tiny organisms and bacteria, but also transform the rocks to block a higher-than-usual amount of ultraviolet radiation. These altered rocks, known as shocked rocks, have their internal structures modified to reflect UV light while still allowing sufficient sunlight for photosynthetic bacteria to flourish.
To date, the conditions resulting from meteorite impacts are among the few environments capable of supporting life on a young, atmosphere-less planet. Similar conditions of pressure, heating, and cooling occur in volcanic settings where lava cools slowly. However, scientists searching for extraterrestrial life are prioritizing impact craters as potential habitats.
4. Lake Cheko
On June 30, 1908, a colossal explosion shook the Podkamennaya Tunguska River region in Siberia. Witnesses reported seeing brilliant lights across hundreds of square kilometers. Upon investigation, vast stretches of trees were found flattened.
The cause of the explosion has been a topic of debate for decades, primarily because no impact crater from a presumed meteorite has been discovered. While some attribute the event to extraterrestrial activity, most scientists believe they have finally uncovered the explanation.
In 1999, a team from Italy's Marine Science Institute in Bologna conducted measurements at nearby Lake Cheko, located a few miles north of the estimated blast epicenter. They discovered the lake wasn't a typical round, basin-shaped crater but rather the result of a low-angle impact that carved a trench into the Earth.
They propose that a rock fragment roughly 10 meters (30 ft) long survived vaporization and struck the ground at a relatively slow speed for an extraterrestrial impact—about 1 kilometer per second. Upon impact, it melted the permafrost, creating the lake's unusual shape and funnel-like bottom. Drilling samples from the lake supported this theory.
3. The Impact Crater With No Extinction Event
The Chicxulub crater in Mexico gained fame when it was identified as the primary cause of the dinosaurs' extinction around 65 million years ago. Such extinction events typically accompany meteorites of that magnitude, with the potential exception of a meteorite that struck Australia approximately 300 million years ago.
The Australian crater is now buried beneath the surface. More precisely, it consists of two massive domes, likely formed when an enormous asteroid split upon impact, creating dual craters.
When compared to the dinosaur-extinction crater, the Australian site becomes even more alarming. Chicxulub spans about 180 kilometers (110 mi), with its asteroid estimated at 10 kilometers (6 mi) wide. In contrast, the Warburton Basin asteroid's impact zone in Australia is twice as large and lies buried 30 kilometers (20 mi) underground.
A geothermal research team uncovered the Australian crater but found no corresponding extinction event, despite it being the largest impact site on Earth. Magnetic imaging reveals the devastation and rock deformation caused by the collision, which should have triggered a significant shift in Earth's life forms at the time.
Additionally, scientists have yet to identify an ash layer or other markers in the rock strata indicating the aftermath of the massive explosion that must have occurred. While we've discovered the planet's largest impact scar, the consequences of the event remain a mystery.
2. The Asteroid Destroyers
Numerous smaller meteorites, known as L-chondrites, have landed on Earth without creating massive craters. For years, scientists were baffled by the origin of these space rocks, many of which fell approximately 460–470 million years ago.
The Thorsberg quarry in Sweden, famous for its pink limestone, has also revealed numerous fossilized meteorites over time. In 2011, workers discovered a 470-million-year-old rock unlike anything seen before. Dubbed the 'mysterious object,' it defies easy classification. While structurally similar to primitive achondrites, it is not an L-chondrite.
To date, all meteorites discovered in the quarry originate from the same catastrophic event: the collision of two celestial bodies. Until recently, only remnants of one of these bodies, which struck Earth around 470 million years ago, had been found. However, the 'mysterious object' likely represents a fragment of the other body involved in the collision—the asteroid destroyer.
It took roughly one million years for fragments of the shattered asteroid to reach Earth. This particular piece has enabled scientists to identify spinels, the unique minerals left behind by various types of meteorites. The distinct signatures of these minerals will help researchers estimate the number of meteorite impacts on Earth over the past 2.5 billion years.
1. The Popigai Diamonds
The Popigai crater, spanning roughly 100 kilometers (60 mi) across the remote Siberian plains, was created around 36 million years ago by an asteroid estimated to be 8 kilometers (5 mi) wide. According to the Novosibirsk Institute of Geology and Mineralogy, the impact also left behind trillions of carats of diamonds.
Russia claims to have been aware of these diamond reserves since the 1970s but kept them secret to avoid destabilizing the diamond market and devaluing their Mirny mine. With the mine now closed, they are prepared to tap into this resource, which contains diamonds twice as hard as conventional ones.
Geologists at Colgate University suggest several possibilities for how Russia acquired this diamond treasure. The meteorite might have struck a diamond-rich kimberlite vein, a volcanic deposit already known in Siberia. While the impact could theoretically have produced super diamonds, such an outcome is highly unlikely.
Another possibility is that the meteorite contained carbon structures that were instantly transformed into diamonds upon impact. Alternatively, the carbon-rich region may have existed on Earth beforehand, with the impact triggering diamond formation.
