A team of South Korean scientists has uncovered new evidence that could help explain how Earth’s atmosphere became rich in oxygen, one of the most transformative events in the planet’s history. Researchers from the Korea Institute of Geoscience and Mineral Resources (KIGAM) report the finding of stromatolites, layered structures formed by microbial communities, within the Hapcheon impact crater on the Korean Peninsula. While the Hapcheon crater is only about 40,000 years old, it shows how stromatolites got a boost from the heat in impact crater hydrothermal systems.