Researchers questioned whether a fungus found in ancient ocean sediments 2 km below the seafloor actually came from 20 million years ago or was modern contamination. By analyzing DNA repetitive sequences in different fungal populations, they discovered the strain was genetically almost identical to modern fungi from Asia, not ancient at all. The extreme conditions in the deep sediments would make it impossible for fungi to survive or exchange genes for millions of years, proving the fungus came from surface contamination during drilling rather than ancient times.