SEDIMENTARY deposits in the Middle Awash research area of Ethiopia's Afar depression have yielded vertebrate fossils including the most ancient hominids known. Radioisotopic dating, geochem-ical analysis of interbedded volcanic ashes and biochronological considerations place the hominid-bearing deposits at around 4.4 million years of age. Sedimentological, botanical and faunal evidence suggests a wooded habitat for the Aramis hominids.