Shallow oceans were poisoned by hydrogen sulphide during a mass extinction event at the end of the Triassic period, 201 million years ago, reports a paper published online this week in Nature Geoscience. The poisoning may have slowed the recovery of marine ecosystems during the early Jurassic period.

Bas van de Schootbrugge and colleagues pieced together shallow marine ecosystems during the extinction at the end of the Triassic period, using information stored in rocks formed at the time. They find evidence of a bacterium that thrives on hydrogen sulphide, indicative of a hydrogen-sulphide-rich ocean. Although these particular bacteria thrive on it, hydrogen sulphide is poisonous to most marine organisms, many of which are known to have gone extinct during this period.