Detected through their molecular remains, fossils of early sponges have been observed in ancient rocks in Oman. The fossils occur in strata that underlie a cap carbonate dated at >635 million years ago. This discovery suggests that shallow waters contained dissolved oxygen in concentrations sufficient to support early animal life at least 100 million years before the Cambrian explosion. Members of NAI’s MIT team led the effort, and publish their findings in the current issue of Nature.