[Reading Science] Hapcheon Impact Crater Unlocks the Secret of Earth's Oxygen Surge

A new clue to the long-standing mystery of the "Great Oxidation Event," when Earth's atmospheric oxygen levels surged about 2.4 billion years ago, has emerged from the only meteorite impact crater on the Korean Peninsula.

A research team from the Korea Institute of Geoscience and Mineral Resources (KIGAM) has identified stromatolites-signature traces of early life on Earth-at the Hapcheon meteorite impact crater in Gyeongnam Province. For the first time, they have proposed the possibility that the hydrothermal lake formed after the meteorite impact may have served as a "breeding ground" for oxygen-producing microorganisms.

Panoramic View of Hacheon Meteorite Impact Crater. Provided by the Korea Institute of Geoscience and Mineral Resources (KIGAM)

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On April 15, KIGAM announced that the research team led by Dr. Jae-Soo Lim had discovered several stromatolites, each measuring 10 to 20 centimeters in diameter, in the northwestern part of the Hapcheon meteorite impact crater. Their analysis, published in the international journal Communications Earth & Environment, concluded that these stromatolites grew in a hydrothermal lake environment formed after the meteorite impact.

Stromatolites are dome-shaped or columnar structures created by microorganisms such as cyanobacteria, which trap layers of sediment. They are considered representative fossils of life activity from about 3.5 billion years ago. As evidence of microorganisms that produced oxygen through photosynthesis, stromatolites are a crucial clue for research into changes in Earth's early atmosphere.

The research team believes that after a giant meteorite struck Hapcheon, a crater formed, groundwater and rainwater accumulated, and a lake was created. Over time, impact melt from deep underground released heat, establishing a hydrothermal lake environment.

Photos of stromatolites discovered at the Hapcheon meteorite impact crater site. Provided by KIGAM

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In fact, the stromatolites exhibited both the influence of the meteorite and the characteristics of the surrounding rock. Analysis of rare earth elements revealed anomalously high values of europium (Eu), a hallmark of hydrothermal activity. These features were especially pronounced in the core, indicating vigorous hydrothermal activity during the early growth stages, which gradually cooled over time.

The greatest significance of this study is that the hydrothermal lake may not have been just a geological phenomenon, but may have served as an "oxygen oasis" in early Earth. The researchers proposed that frequent meteorite impacts in early Earth created numerous hydrothermal lakes, where cyanobacteria and stromatolites thrived and locally supplied oxygen.

This offers a new scenario for explaining why atmospheric oxygen levels rose so sharply during the Great Oxidation Event. Previously, changes in volcanic activity, continental growth, and ocean chemistry were mainly discussed, but this study adds a new perspective: "Meteorite impacts may have expanded habitable environments and accelerated oxygen production."

A conceptual diagram sequentially illustrating the evolution of the Hapcheon impact crater formed by a meteorite collision into a high-temperature, high-salinity lake through hydrothermal activity; stromatolites growing at the edges produce oxygen; and as the hydrothermal activity weakens, the landscape and vegetation transform into their current state. Provided by KIGAM

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The research team has also extended these findings to Mars exploration strategies. They suggest that, similar to early Earth, ancient meteorite impact craters on Mars-where water is believed to have once existed-may preserve traces of life similar to stromatolites.

They explained that future Mars exploration should focus on searching for sedimentary and organic layers, as well as layered rock structures, in the outer rims of craters, as these could be key indicators in the search for evidence of life.

Dr. Jae-Soo Lim, the first author of the paper, stated, "This is the first comprehensive demonstration that stromatolites grew in a hydrothermal lake environment within a meteorite impact crater. The study is significant as it presents a new possibility for oxygen oases as a cause of the Great Oxidation Event on early Earth, and offers a novel perspective for Martian surface exploration."

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