Origin of life from apatite dating? Reply

Mojzsis et al.1,2 reported the carbon-isotope composition of carbonaceous inclusions in grains of apatite from sediment sequences of Akilia island, southwest Greenland, that are more than 3,850 million years (Myr) old. The δ13C values measured by Mojzsis et al.1 led them to conclude that these carbonaceous materials are evidence of early life 3,850 Myr ago. But if other isotopes (U-Pb and Pb-Pb) are used, the apatites are estimated at just 1,504±336 (2σ) and 1,459±160 (2σ) Myr old. This value is consistent with measurements of 1,600-1,700 Myr for Rb-Sr mineral isochrons on biotites3 and 1,670 Myr for K-Ar muscovite4 from Amitsog gneiss in the region. We conclude that, about 1,500 Myr ago, these apatites in Akilia island experienced a metamorphic event of about 600 °C (estimated by the closure temperature of the U-Pb system5,6).