The space rock that crashed into Earth 66 million years ago, at the end of the Cretaceous, caused a global calamity that doomed the dinosaurs and many other forms of life. But that was by no means the largest meteorite that hit our planet.
One 200 times larger fell 3.26 billion years ago, triggering global destruction on an even larger scale. But, as new research shows, that disaster may have been beneficial to the early evolution of life by serving as “a giant fertilizer pump” for the bacteria and other single-celled organisms called archaea that dominated at the time, providing access to key nutrients phosphorus and iron.
Researchers evaluated the effects of this meteorite impact using ancient rocks from a region of northeastern South Africa called the Barberton Greenstone Belt. They found abundant evidence, especially from the geochemical signature of the preserved organic matter, but also from fossil mats of marine bacteria, that life recovered with aplomb. “Life not only recovered quickly once conditions returned to normal within a few years or decades, but actually thrived,” said Harvard University geologist Nadja Drabon, lead author of the study published Monday in the journal Proceedings of the National Academy of Sciences.
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Earth was a very different place during the Paleoarchaean Era, when this occurred, and meteorite impacts were larger and more frequent.
“At this time, the Earth was a kind of aquatic world, with a limited appearance of volcanoes and continental rocks. There was essentially no gas or oxygen in the atmosphere or oceans, nor cells with nuclei,” explained Andrew Knoll, a Harvard geologist and co-author of the study.
The meteorite was of a type called carbonaceous chondrite, which is rich in carbon and also contains phosphorus. Its diameter was about 37-58 km, Drabon said, making it about 50-200 times the mass of the asteroid that wiped out the dinosaurs, as well as their avian descendants.
“The effects of the impact would have been swift and ferocious. The impactor hit with so much energy that it and any sediment or rock it collided with vaporized. This cloud of rock vapor and dust expelled from the crater would have circled the globe and blackened the sky in a matter of hours,” explains Drabon.
“It is likely that the impact occurred in the ocean, starting a tsunami that swept the entire planet, tearing up the seabed and flooding the coasts. Finally, much of the energy from the impact would be transformed into heat, which would mean that the atmosphere would begin to heat up so much that the upper layer of the oceans would begin to boil,” Drabon added.
According to Drabon, it likely took several years to decades for the dust to settle and for the atmosphere to cool enough for water vapor to return to the ocean. Microbes that depend on sunlight and those that live in shallow water would have been decimated.
But the meteorite would have provided a large amount of phosphorus, a nutrient for microbes crucial for the core molecules that store and transmit genetic information. The tsunami would also have mixed iron-rich deep water with shallower water, creating an ideal environment for many types of microbes because the iron provides them with an energy source.
“Let’s imagine these impacts as giant fertilizer bombs,” explains Drabon.
“We think of meteorite impacts as something disastrous and harmful to life; The best example is the Chicxulub impact (in the Yucatan Peninsula), which caused the extinction not only of the dinosaurs, but also of 60-80% of the animal species on Earth,” Drabon explained. “But 3.2 billion years ago, life was much simpler.”
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“Microorganisms are relatively simple, versatile and reproduce at high speed,” Drabon explained.
Evidence of the impact included chemical signatures of the meteorite, small spherical structures formed from rock molten by the impact, and chunks of seafloor mixed with other tsunami-churned debris in sedimentary rock.
“Primitive life withstood a gigantic impact,” Drabon said.
With information from Reuters
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