ðə hˈɑːmɪnˌɪdbˈɛɹɪŋ lˈeɪɚz ɑːɹ fˈoːɹ.fˈoːɹ mˈɪliən jˈɪɹz ˈoʊld, ɐkˈoːɹdɪŋ tə ɹˌeɪdɪoʊˌaɪsətˈɑːpɪk dˈeɪɾɪŋ, dʒˌiːoʊkˈɛmɪkəl ɛɡzˌæmᵻnˈeɪʃən ʌv ˌɪntɚbˈɛdᵻd vɑːlkˈænɪk ˈæʃᵻz, ænd bˌaɪoʊkɹˌɑːnəlˈɑːdʒɪkəl fˈæktɚz.
The hominid-bearing layers are 4.4 million years old, according to radioisotopic dating, geochemical examination of interbedded volcanic ashes, and biochronological factors.