Discovery of stromatolite formation in post-impact hydrothermal lacustrine environments and its implications for early Earth

Abstract Understanding asteroid-collision-generated extreme environments, including hydrothermal activity, is crucial for gaining insights into biological evolution on the early Earth. Here, we demonstrate that stromatolites—the oldest fossil evidence of oxygen-producing microbial life on early Earth—could have developed within impact craters, based on a detailed investigation of stromatolites and lake sediments in the Hapcheon impact crater, Korea. Our study revealed that the Hapcheon impact event occurred 42,300 ± 1000 years before the present (cal yr BP) from radiocarbon ages of charcoals included in the impact breccias at 100 ~ 140 m depth underground, and stromatolites formed at the lake margin under the post-impact hydrothermal conditions, as indicated by positive Europium anomaly in the stromatolites. Furthermore, significantly depleted Osmium isotope ratios in the stromatolites support the possible meteoritic influence. Considering the frequency of asteroid collisions during the early Earth, stromatolite blooms in impact craters could be one of the active oxygen oases that led to the creation of habitable environments on the early Earth.