|Title:||Oxygen‐isotope evidence from ancient zircons for liquid water at the Earth’s surface 4300 Myr ago|
|Authors:||S.J. Mojzsis, T.M. Harrison, and R.T. Pidgeon|
|Publication:||Nature, v. 409, p. 178‐181.|
Granitoid gneisses and supracrustal rocks that are 3,800‐4,000 Myr old are the oldest recognized exposures of continental crust. To obtain insight into conditions at the Earth’s surface more than 4Gyr ago requires the analysis of yet older rocks or their mineral remnants. Such an opportunity is presented by detrital zircons more than 4Gyr old found within 3‐Gyr‐old quartzitic rocks in the Murchison District of Western Australia. Here we report in situ U‐Pb and oxygen isotope results for such zircons that place constraints on the age and composition of their sources and may therefore provide information about the nature of the Earth’s early surface. We find that 3,910‐4,280Myr old zircons have oxygen isotope (δ18O) values ranging from 5.4±0.6‰ to 15.0±0.4‰. On the basis of these results, we postulate that the ⁓4,300‐Myr‐old zircons formed from magmas containing a signifcant component of re‐worked continental crust that formed in the presence of water near the Earth’s surface. These data are therefore consistent with the presence of a hydrosphere interacting with the crust by 4,300Myr ago.