Stromatolites found beneath an asteroid’s crater suggest that the impact created a hydrothermal lake capable of supporting microbial communities for thousands of years. The phenomenon may have been common on early Earth, favoring the emergence of oxygen and life.
Somehow, on this beautiful blue planet we call Earth, the extraordinary phenomenon we call life emerged a long time ago, spreading until it covered virtually every corner of the globe.
One current of thought proposes that the intense asteroid bombardment that the Earth suffered around 4 billion years ago played a role in that process – that, without all those rocky fragments colliding with our planet, we might not be here today.
Now, a new one, recently published in the magazine Communications Earth & Environmentsuggests that the effect of asteroids may have been even more complex than previously thought.
Beneath a crater excavated by a large impact around 42,000 years ago, a team led by geologist Jaesoo Limfrom the Korea Institute of Geosciences and Mineral Resources (KIGAM), identified several stromatolites.
Stromatolites are layered structures formed by microbial matssimilar to some of the oldest known traces of life on Earth.
This discovery suggests that the heat generated by impacto may have created a long-lasting hydrothermal environment, similar to that of hot springs, where microbial communities would be able to thrive.
It’s possible that during the great bombardment era billions of years ago, impact craters like these created countless temporary shelters to the first life forms across the young Earth.
The story of the origins of life is nebulous; It remains unclear when and how inanimate components combined to trigger the processes that define biology.
A fundamental cluehowever, can be found in stromatolites.
In several places around the world, these layered rock structures, built by microorganisms such as cyanobacteria, similar to the calcium carbonate skeleton of corals, have been found with dates dating back to 3.5 billion years.
These are some of the oldest traces of life that our planet has offered us, says . However, there is still much to know about how these communities emerged and spread. Trying to understand it is a bit like trying imagine a puzzle with 1000 pieces having only 7 in hand.
A Jeokjung-Chogye Basinat Hapcheon, may have just added a few more pieces, giving new context to discoveries associated with impact craters like , where evidence of microbial mats had been interpreted as material dragged into the craterand not as communities that naturally formed there.
Although the basin is a well-known depression in the landscape of the Korean peninsula, its origin as impact structure It was only recognized relatively recently, having been revealed in 2021.
Now, while excavating the northwestern part of the crater, Lim and his colleagues have found various stromatolites with diameters between 10 and 20 centimeters.
It had already been established that a impact crater can fracture and heat the Earth’s crust at the affected location, creating a system in which the residual heat, when slowly dissipating, heats the water that fills the resulting depression – one impact hydrothermal lake.
The researchers concluded that these stromatolites were probably formed in exactly that kind of environment. The team analyzed its mineral content and found traces of an element called Europewhich becomes much more soluble in hot hydrothermal fluids.
The presence of europium is usually interpreted as a signature of past hydrothermal activity; represents a strong signal suggesting that the lake that once filled the Jeokjung-Chogye Basin was hydrothermal in nature.
Other signatures corroborate this interpretationnamely high levels of calcium, calcite and sulfur associated with microbes adapted to hot environments, found in sediments.
Radiocarbon dating of a sample suggests that the stromatolites formed approximately 23,400 and 14,600 yearswhich indicates that the hydrothermal lake remained active for a few tens of millennia.
The discovery also offers a glimpse into how primeval Earth may have become to support life; the results show that the impact of an asteroid can inadvertently create the ideal environment for microbes.
If the early Earth was densely scarred with impact craters during the initial bombardment, before the inner Solar System stabilized, it may have hosted many such refuges.
And this is where the subject becomes even more interesting.
To primitive Terra had very little oxygen before about 2.4 billion years ago. Scientists believe that the appearance of the first photosynthetic life forms, such as cyanobacteriawas at least partially responsible for the air we breathe today. There is also evidence that oxygen may have been a byproduct of microbial metabolism who built the stromatolites.
If so, early bombardment may have created pockets of oxygen production around the world, what researchers call «oxygen oasis».
“This is the first comprehensive evidence to suggest that stromatolites could be form in hydrothermal lakes created by asteroid impacts,” says Lim. “These environments may have provided favorable conditions for the first microbial ecosystems.”
The interpretation is somewhat speculative. Current data are far from proving the role that stromatolites eventually played in Earth’s oxygenation.
Still, the discovery reinforces the idea that life on Earth may have emerged through athe combination of ingredients and events relatively rare, that we have not yet found anywhere else in the Universe.
Other impact craters on Earth need to be investigated in detail to determine whether stromatolite-rich hydrothermal lakes may have contributed to the increase in oxygen in Earth’s atmosphere.
Furthermore, this result suggests that there is still hope of finding similar signatures elsewhere. To the impact craters on Marsfor example, can store the buried remains of stromatolites, yet to be discovered.
