When did animal life on earth begin? As of this week, we can now say the evidence for the earliest animals dates to 635 million years ago, according to a paper in this week's Nature.
An international team of scientists from UC Riverside, the Massachusetts Institute of Technology and other institutions discovered carbon biomarkers for sponges dating to 100 million years before the monumental Cambrian explosion, when animal life diversified rapidly.
"Our findings suggest that the evolution of multicellular animals began earlier than has been thought," said Gordon Love, an assistant professor of Earth sciences, who led the research group. Love began working on the project while he was a postdoctoral researcher at MIT.
He added, "Moreover, sponges live on the seafloor, growing initially in shallow waters and spreading, over time, into deeper waters, implying the existence of oceanic environments which contained dissolved oxygen near the shallow seafloor around 635 million years ago."
Love believes the climatic shock of the extensive glacial episodes of the Neoproterozoic era (1000-542 million years ago) likely caused a major reorganization of marine ecosystems, perhaps by irrevocably altering ocean chemistry.
"This paved the way for the evolution of animal feeders living on the seafloor," he said. "We believe we are converging on the correct date for the divergence of complex multicellular animal life, on the shallow ocean floor between 635 and 750 million years ago."
Love and his team were funded by Petroleum Development Oman; the NASA Exobiology Program; the National Science Foundation Division of Earth Sciences; the Agouron Institute; and the NASA Astrobiology Institute. The scientists are already planning their next project.
Love said, "We aim to investigate the environmental context by which multicellular animal life became viable and flourished."
