RIVERSIDE, Calif. An international team of scientists from UC Riverside, the Massachusetts Institute of Technology and other institutions has found the oldest evidence for animals in the fossil record.
The researchers examined sedimentary rocks in south Oman, and found an anomalously high amount of distinctive steroids that date back to 635 million years ago, to around the end of the last immense ice age. The steroids are produced by sponges one of the simplest forms of multicellular animals.
The researchers argue that the discovery of the sponges is evidence for multicellular animal life beginning 100 million years before the Cambrian explosion, a well-studied and unique episode in Earth history that began about 530 million years ago when, as indicated by the fossil record, animal life diversified rapidly.
The discovery can help scientists reconstruct Earths early ecosystems and explain how animal life may have first evolved on the planet.
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. 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.
Study results appear in the Feb. 5 issue of Nature.
According to Love, 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.
Besides researchers at MIT, Love was joined in the study by colleagues at Geoscience Australia; the University of Newcastle upon Tyne, United Kingdom; the California Institute of Technology; and the University of Nottingham, United Kingdom.
The four-year study was 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.