66 million years ago, a 10-kilometre-wide space rock fell from the sky above what is now the Yucatan Peninsula in the Gulf of Mexico. When it hit Earth, it left a hole the size of Maryland in the Earth’s crust, sparked a global firestorm, and wiped out about 75 percent of species. For the dinosaurs, who drove them to extinction, this event was effectively the end of the world. But out of the ashes rose a survivor, our mammalian ancestors, and a vibrant new era in Earth’s history began. Today, this devastating effect is considered an act of cosmic destruction, without which we as a species would not exist.
But this event’s infamous impactor is nothing compared to the asteroid that crashed into Earth 3.26 billion years ago, during what scientists call the Archean era in Earth’s 4.5 billion year history. did. The Archean space rock, known as S2, was 50 to 200 times larger and was large enough to blast at least 10,000 cubic kilometers of evaporated rock into the sky before recondensing into molten liquid. It became droplets and rained down on the earth. Unsurprisingly, these conditions “would have been really catastrophic for early life,” says Nadja Drabon, a geologist at Harvard University. But her latest research shows that, like the more famous space rock crash that killed off the dinosaurs, this much larger and much earlier impact also had an upside, providing a powerful boost to Earth’s early biosphere. It suggests that it was given.
“What we discovered was really surprising,” Drabon says. In collaboration with several colleagues, we examined South Africa’s rock formations and found that in addition to producing enough evaporated rock to burn the world, the S2 impact also caused a massive tsunami that destroyed the largest part of the ocean. It turned out that the upper layer was boiled. But it also pumped phosphorus and other bio-essential elements into the world’s nutrient-starved oceans, sparking a blooming of life.
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And while the dinosaur-killing impact left behind millions of years of ecological destruction, the catastrophic aftereffects of this much larger impact were so short-lived that chemical analyzes of rock formations wouldn’t show them, says Drabon. he says.
Conditions have been bad “for years, maybe decades,” she says. “But then life would pick up really quickly.” Her new study says today. Proceedings of the National Academy of Sciencessuggests that mega-impacts had an even greater impact on Earth’s early biosphere than previously realized, and that Earth’s Archean inhabitants were much more resistant to these types of shocks than modern organisms. It suggests that.
unrecognizable earth
If we had been flying over Earth just before the S2 impact over 3 billion years ago, the Earth would have looked very different than it does today.
“Earth was largely a water world,” said Andrew Knoll, a geobiologist at Harvard University who collaborated with Drabon on the new study, with only a few volcanoes and large islands rising above sea level. That’s what it means. The world’s oceans may have contained twice as much water as they do now because the Earth’s interior was not cool enough to absorb as much water as it currently holds.
Without the erosion of large continents and the washing away of minerals into rivers, the oceans would lack important nutrients such as phosphorus, copper, molybdenum, and nickel. The atmosphere and oceans similarly contain little free oxygen. Free oxygen currently makes up more than 20 percent of Earth’s air and sustains animals, plants, and fungi. Knoll said Earth probably contained only 1 to 2 percent of today’s life, all in the form of single-celled microorganisms.
Part of that sparse biome is powered by a primitive form of photosynthesis, in which microbes use sunlight to extract electrons from iron dissolved in seawater, thereby converting carbon dioxide into sugars. Can be done. However, the surface layer of the ocean, where light is available, contains only trace amounts of iron, making it difficult for even these hardy creatures to make a living. These oceans were “biological deserts,” Drabon said. This is why experts often imagine the early Earth to be a quiet, boring place.
A spherule collected from an Archean impact layer. Coins are used for the scale. Thick layers of these tiny spheres in Archean rocks, formed from molten debris rained down by asteroid impacts, are direct evidence of catastrophic impact events in Earth’s early history.
In the late 1980s and 1990s, geological discoveries dramatically changed that perspective. For example, in the Archean geological formations of South Africa, geologists Donald Rowe and Gary Byerly, now at Stanford University and Louisiana State University, respectively, have found mineral spheres the size of sand grains in at least eight layers of rock. I found that it was crowded. These tiny “globules” turned out to be solidified droplets of lava that fell after a series of large-scale impact events. Although these impact craters would have long since eroded away, the thick layer of spherules suggests that they still happened and happened with surprising frequency. Based on their study of geological formations, Lowe and Byerly estimated that an object larger than the dinosaur killer struck Earth at least once every 15 million years between 3.5 billion and 3.2 billion years ago. . This was much more frequent than it is now. They estimated that some of those asteroids may be up to 350 times heavier than the dinosaur killer.
From boiling pot to paradise
Drabon, a former graduate student at Lowe University, wondered how these literally earth-shaking impacts affected the Archean biosphere. She spent years collecting rocks from several meters directly above and below the impact layer of the aforementioned S2, one of the famous events. Both types of rock were formed from sediments deposited on shallow coastal seafloors near rare lands. Before the cataclysm, the rock beneath the impact layer was filled with a fine black layer of ancient organic carbon. This is the remains of a slimy mat of microbes that once thrived on the ocean floor before being buried, crushed and cooked by common geological processes. These gentle, flat layers probably accumulated over thousands of years. What was right on top of them happened much more quickly.
The layers of spherules, as tall as several bed mattresses in some places, are jumbled with sand and pebbles, evidence of a series of tsunami waves that scraped and mixed the ocean floor in the hours after impact. It becomes. Above the impact debris is a thick layer of petrified mud, likely formed over days or weeks as fine-grained silt thrown up by waves settled on the ocean floor. There was something on the mud that fascinated Drabon. It is a small hexagonal salt crystal deposited by the sudden evaporation of salty seawater. The crystals were a sure sign that the impact “really heated the surface and started boiling some of the (ocean) water,” Drabon said.
She, Knoll, and her other co-authors (including Lowe) argue that meters to tens of meters of water were instantaneously heated into steam. If that had actually happened, “a huge amount of bacteria” would have been killed, Knoll said. Debris thrown into the atmosphere would then have blocked the sun for months or even years, making life even more difficult for the surviving photosynthetic microorganisms.
But things will calm down soon.
A few meters above the impact layer, the rock is once again filled with a black, carbon-rich microbial layer, perhaps even more dense than the layer below, “perhaps indicating that life bloomed after the impact.” “There are,” Drabon said.
She and her team argue that such blooming was caused by several factors. The rock layer above the impact contains high levels of phosphorus. Phosphorus is an important nutrient used in biology to manufacture everything from DNA to cell membranes. They estimate that the S2 asteroid could have transported 360 billion tons of extraterrestrial phosphorus into Earth’s starved oceans. Even more elements may have found their way into the ocean through large amounts of rock and silt eroded from the tsunami-hit islands.
A schematic diagram showing the environmental destruction and subsequent recovery caused by a giant asteroid collision approximately 3.26 billion years ago. After a chaotic period when dust ejected by the impact darkened the skies and tsunamis hit boiling oceans, nutrients released by the commotion helped revive life.
The microbial layer above the impact site is also littered with a red, rusty iron mineral called siderite, likely formed from iron-rich water stirred up from deep by turbulent tsunami waves. This influx likely supercharged iron-dependent photosynthetic bacteria that were already loaded with phosphorus transported by the shock, further promoting bloom.
Drabon also looked at the ratio of heavy and light carbon isotopes, or carbon atoms with different atomic masses, in the dark microbial layer above and below the impact. This could provide clues as to the types of organisms that were present. This is because different types of organisms absorb heavy and light carbon isotopes at different rates. It revealed something important.
“We see changes in carbon isotopes,” Drabon said, suggesting that the mix of microorganisms changed after the impact. “A new major metabolism is occurring” in the ocean, she says. And that likely reflects an increase in microorganisms that use iron to generate energy through photosynthesis and other pathways.
Microbes vs. Mammoth
This new evidence that life blossomed after the S2 impact is “a very interesting discovery,” said Alexandra Davatzes, a geologist at Temple University who studies Archean impacts. She points out that other major disruptions in the Earth’s environment are also intensifying the biosphere, such as the “Snowball Earth” phenomenon, thought to have occurred 700 million and 635 million years ago. During these events, glaciers spread across much of the world’s surface and likely wiped out much life. But when the ice eventually receded, vast amounts of glacier-pulverized, nutrient-rich rock were dumped into the ocean to encourage biological recovery.
Eva Steuken, a geobiologist who studies the Archean Earth at the University of St. Andrews in Scotland, believes Drabon’s work could lead to further discoveries.
“There are certainly a lot of (shocking) events that we’ve missed,” she says. After all, no Earth impact craters from that time are known to have survived to the present day. And the layers of spherules scattered across our planet by these collisions are not guaranteed to be preserved in such old rocks. But as evidence of previously unknown impacts is discovered, we’re not only learning how these events caused severe damage to Earth’s biosphere, but also how they helped heal those wounds. , our awareness may increase.
And Steuken wonders if S2 and other giant impacts also supported life in other ways beyond what Drabon suggests. Violent impacts from incoming asteroids may have pulled an even more important nutrient, nitrogen, out of the atmosphere and delivered it to the ocean in a chemically reactive form that could be absorbed by microorganisms. “That’s something I’m excited to explore,” she says.
Simone Marchi, a planetary scientist at the Southwest Research Institute in Boulder, Colorado, believes there are important lessons to be learned from the S2 collision. He says there is an “interesting interaction” between asteroid impacts and the types of life present at the time of impact. Unlike Brontosaurus or Mammoth, the microbe can survive extreme heat, dehydration, and radiation by forming cysts, or spores, that persist for years. And microbes are collectively highly resilient to environmental damage in countless other ways. If one microorganism in a billion survives, it can replenish all microorganisms because it grows and divides so quickly.
“Life at that time could withstand the impact of S2,” Marchi says. But what if this much larger asteroid had crashed into Earth 66 million years ago, after flowers, trees, dinosaurs, mammals, fish, and other complex life had evolved?
“Only a simple life could survive in this kind of event,” he says. Rather than extinguishing the dinosaurs and leaving mammals, birds, and fish unscathed, the impact could have wiped out all plants and animals. “It would completely reset life and bring it back to the bacterial level,” Marchi says.
