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How did life on Earth come about? How did he survive the Aeon Hadean, a period in which repeated massive impacts carved craters thousands of kilometers across the earth’s surface? Those impacts turned Earth into a hellish place, where the oceans turned to vapor and the atmosphere was filled with rock vapor. How could a living being survive?
Ironically, those same devastating impacts may have created a vast underground refuge for the first few years of Earth’s life. In the midst of all those chambers and paths, filled with mineral-rich water, primitive life found the refuge and energy needed to keep life on Earth alive. And the evidence comes from the best-known extinction event on Earth: the Chicxulub impact event.
A new study presents evidence that the Chicxulub crater housed an enormous underground network of hydrothermal vents that could have provided a sanctuary for microbial life.
By extension, the very earlier impact craters likely provided the same sanctuary. The study is titled “Microbial Sulfur Isotope Fractionation in the Chicxulub Hydrothermal System”. The lead author is David Kring of the Lunar and Planetary Institute. It is published in the journal Astrobiology.
The idea that life may have arisen and persisted in the web beneath the impact craters is called the life impact origin hypothesis. David Kring is one of the leading scientific voices in support of this hypothesis.
While massive repeated impacts rendered the Earth’s surface uninhabitable during the Aeon Hadean, the same was likely not true of the region beneath the impact craters.
According to Kring, those same impact events “… were producing vast underground hydrothermal systems that were perfect crucibles for pre-biotic chemistry and habitat for the early evolution of life.”
In this new study, Kring and her colleagues present evidence from the International Ocean Discovery Program and the International Continental Scientific Drilling Program.
Those programs provided rock cores from the Chicxulub crater ring. Specifically, this study is based on approximately 15,000 kilograms (33,000 lbs) of rock recovered from a 1.3 km (0.8 miles) deep well.
(David A. Kring)
Above: Section of the Chicxulub core with the hydrothermal minerals dachiardite (bright orange) and analcime (colorless and transparent). The minerals partially fill the cavities in the rock that were niches for microbial ecosystems.
The team of researchers found tiny pyrite spheres called yaws in the sample, only 10 millionths of a meter in diameter.
Since pyrite is an iron sulfide, it contains sulfur isotopes. Those isotopes showed that the yaws were made up of microbes, and those microbes were part of an ecosystem adapted to the heated mineral laden fluid flowing through the underground network. That net was present under the shattered ring of the Chicxulub impact crater.
Life needs energy to survive and this microbial life got its energy from chemical reactions in the rock and fluid system.
They converted the sulfate in the fluid to sulfide, which was then stored as pyrite. These ancient thermophilic microbes would have been quite similar to the thermophilic microbes that inhabit extreme environments on today’s Earth, such as deep ocean hydrothermal springs and hot springs in Yellowstone Park.
In their article the authors write:
“Sulfur isotope analyzes of pyrite phramboids in the impact breach from the Chicxulub crater indicate that thermophilic colonies of sulfate-reducing organisms inhabited the porous, permeable rock beneath the crater floor and fed on sulfate carried through the rock through a hydrothermal system generated by the impact. “
They add that the same sulfur-reducing organisms persisted for 2.5 million years after impact and that the organisms found under Chicxulub are now likely the direct descendants of those earlier organisms.
This study comes at the end of 20 years of research into the origin of the impact of the life hypothesis. Dr. Kring’s involvement began earlier when he co-authored a 1992 study that linked the Chicxulub crater to the KT boundary mass extinction. Dr Kring was also involved in research which showed that the region beneath the Chicxulub crater was porous.
Subsequent research showed that the region was crisscrossed by a vast system of hydrothermal vents. Now, this study shows that the vent system housed life.
It has been a long and arduous journey towards this latest discovery. The timing and duration of the bombing during the Hadean was difficult to establish, as none of the craters of the terrestrial Hadean are still around. The study of lunar craters and lunar samples from the Apollo missions showed that the Moon was subjected to intense bombardment for about 400 million years during the Hadean. Earth would suffer from the same episode.
Chicxulub crater is the only reasonable proxy for a Hadean crater. So the crater is a way to develop and test the origin of the impact of the life hypothesis.
As the authors write in their article, “Chicxulub is the only large peak ring basin that is still intact and offers the opportunity to study the remains of an impact-generated hydrothermal system, from depth to the surface environment of including vent. to those that may have existed earlier in the history of the Earth. “
It also took time and effort to establish how long the vast hydrothermal systems under these craters have existed. The question was: Did they last long enough for evolutionary processes to occur and for biological material to migrate to adjacent impact craters and their systems?
Extensive modeling showed that the vent systems were long-lived enough for both to happen.
The authors write: “The thermal evolution models of this and other hydrothermal systems indicated that they were long-lasting and produced significant volumes of porous and permeable rock suitable for thermophilic organisms.”
There is still much work to be done to confirm the origin of the impact of the life hypothesis. In a two-page summary, Dr. Kring outlines some of that work.
First of all, the carrot samples from the Chicxulub crater need further study. Kring wants to retrieve more information from those samples on the evolution – both thermal and chemical – of the hydrothermal vent system.
There is also a need for a better understanding of the energy available for microorganisms in the granitic crust that was present during the Hadean.
And to clarify the chronology of impacts to Earth, researchers need more samples from lunar impact basins such as the Aitken South Pole Basin and others.
But the icing on the cake could be the search for samples of the Earth adea on the moon itself.
“If it were possible to locate sedimentary and fossil specimens, they would provide a direct record of the early evolution of life on Earth,” writes Kring.
This article was originally published by Universe Today. Read the original article.
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