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Molecular fossils make clear ancient life.

Based on the chemical signatures present in ancient rocks and the genetics of living animals, paleontologists are getting glimpses of life greater than a billion years into the past. The research, published Dec. 1 in Geology and Genetics, shows how changes within the early Earth signaled changes in the best way animals ate.

David Gould, associate professor within the Department of Earth and Planetary Sciences on the University of California, Davis, works within the emerging field of molecular biology, using tools from each geology and biology to review the evolution of life. With recent technology, it is feasible to get better chemical traces of life from ancient rocks, where animal fossils are lacking.

Lipids particularly can survive in rocks for lots of of hundreds of thousands of years. Traces of sterol lipids, which come from cell membranes, have been present in rocks 1.6 billion years old. Nowadays, most animals use cholesterol — a sterol with 27 carbon atoms (C27) — of their cell membranes. In contrast, fungi typically use C28 sterols, while plants and green algae produce C29 sterols. C28 and C29 sterols are also often known as phytosterols.

C27 sterols have been present in rocks 850 million years old, while traces of C28 and C29 appear about 200 million years later. This reflects the increasing diversity of life at the moment and the evolution of the primary fungi and green algae.

Without actual fossils, it's hard to say much about these sterols from animals or plants. But a genetic evaluation by Gould and colleagues is shedding some light.

Don't make it, eat it

Most animals are unable to make phytosterols themselves, but they'll obtain them by eating plants or fungi. Recently, it was discovered that annelids (diatoms, a bunch that features common worms) have a gene that is required to make long-chain sterols. By the genes of various animals, Gould and colleagues created a family tree, first inside annelids, then for animal life basically.

They found that the gene originated very early in animal evolution, after which underwent rapid changes around the identical time that phytosterols appeared within the rock record. After that, most animal lineages lost the gene.

“Our interpretation is that these phytosterol molecular fossils record the rise of algae in ancient oceans, and that animals abandoned phytosterol production when they could easily obtain it from this increasingly abundant food source,” Gould said. could get,” Gould said. “If we're correct, the gene history describes a change in feeding strategies in animals early of their evolution.”

Co-authors on the paper are: at UC Davis, Tessa Brunauer and Chris Mulligan; Ainara Sistiaga, University of Copenhagen; KM Vuu and Patrick Shih, Joint Bioenergy Institute, Lawrence Berkeley National Laboratory; Shane O'Reilly, Atlantic Technological University, Sligo, Ireland; Roger Simmons, Massachusetts Institute of Technology. The work was supported partially by a grant from the National Science Foundation.