Evidence from detrital zircons for the existence of continental crust and oceans on the Earth 4.4 Gyr ago

No crustal rocks are known to have survived since the time of the intense m eteor bombardment that affected Earth(1) between its formation about 4,550 Myr ago and 4,030 Myr, the age of the oldest known components in the Acasta Gneiss of northwestern Canada(2). But evidence of an even older crust is p rovided by detrital zircons in metamorphosed sediments at Mt Narryer(3) and Jack Hills(4-8) in the Narryer Gneiss Terrane(9), Yilgarn Craton, Western Australia, where grains as old as similar to4,276 Myr have been found(4). H ere we report, based on a detailed micro-analytical study of Jack Hills zir cons(10), the discovery of a detrital zircon with an age as old as 4,404 +/ - 8 Myr-about 130 million years older than any previously identified on Ear th. We found that the zircon is zoned with respect to rare earth elements a nd oxygen isotope ratios (delta (18) O values from 7.4 to 5.0 parts per tho usand), indicating that it formed from an evolving magmatic source. The evo lved chemistry, high delta (18) O value and micro-inclusions of SiO2 are co nsistent with growth from a granitic melt(11,2) with a delta (18) O value f rom 8.5 to 9.5 parts per thousand. Magmatic oxygen isotope ratios in this r ange point toward the involvement of supracrustal material that has undergo ne low-temperature interaction with a liquid hydrosphere. This zircon thus represents the earliest evidence for continental crust and oceans on the Ea rth.