Until now, scientists thought the lipid isoarborinol, a fatty molecule, was only produced by flowering plants, or angiosperms. As such, paleontologists interpreted evidence of its ancient presence as proof of dry land.

However, new findings from researchers at the University of Stanford have undermined the assumption. Scientists at Stanford recently discovered isoarborinol-like lipid molecules produced by bacteria floating in the Adriatic Sea.

"Arborinol lipids can be preserved in sedimentary rocks for millions of years, so they can function as 'molecular fossils' that can inform us about the types of organisms and environments on early Earth," Paula Welander, a geobiologist at Stanford, said in a news release.

The latest discovery complicates previous paleontological findings, but solves a 20-year mystery. In the 1990s, researchers discovered evidence of isoarborinol -- molecular fossils -- in sediments dated to the Permian and Triassic eras, roughly 100 million years before the emergence of angiosperms.

Now, researchers have more proof isoarborinol and its relatives were produced by sources other than flowering plants. Such a revelation -- detailed in the journal PNAS -- is likely to force paleontologists to reinterpret much of early fossil record.

"If these lipids are discovered in sediment cores from ancient lakes, the question is, do they represent terrestrial input from flowering plants or were there actually lake bacteria living in low-oxygen environments that were producing them?" Welander asked.

The discovery suggests isoarborinol and its relatives are made in similar ways by bacteria and angiosperms, both of which utilize similar proteins and enzymes.

"It also adds credence to the idea that arborinols in the rock record -- and modern environments, too -- could come from a bacterial source," Welander concluded.