How long have jellyfish lived in the ocean? This jellyfish fossil is from the Cambrian period, more than 500 million years ago. It was found buried in Utah—an area that used to be underwater, covered by the ocean. Fossil jellyfish are rare because they have no bones or other hard parts to turn into fossils. Instead, scientists have to look for so-called "soft fossils," when organisms are quickly buried in sediment, leaving an imprint in the rock. Learn more about jellyfish evolution and diversity.