Sponges were probably one of the earliest animal groups to evolve – but researchers have had trouble working out exactly when in geological time they appeared. Now, an analysis of ancient rocks and oils has turned up traces of steroids made by early sponges that indicate they may have been populating the ancient seafloor at least 120 million years earlier than we thought.

“If animals first appeared in a predominantly bacterial or microbial world, they would need to harness microbes and live symbiotically …