Comment on "Heterogeneous Hadean hafnium: evidence of continental crust at 4.4 to 4.5 Ga".
نویسندگان
چکیده
Harrison et al. (Reports, 23 December 2005, p. 1947) proposed that plate tectonics and granites existed 4.5 billion years ago (Ga), within 70 million years of Earth's formation, based on geochemistry of >4.0 Ga detrital zircons from Australia. We highlight the large uncertainties of this claim and make the more moderate proposal that some crust formed by 4.4 Ga and oceans formed by 4.2 Ga.
منابع مشابه
Heterogeneous Hadean hafnium: evidence of continental crust at 4.4 to 4.5 ga.
The long-favored paradigm for the development of continental crust is one of progressive growth beginning at approximately 4 billion years ago (Ga). To test this hypothesis, we measured initial 176Hf/177Hf values of 4.01- to 4.37-Ga detrital zircons from Jack Hills, Western Australia. epsilonHf (deviations of 176Hf/177Hf from bulk Earth in parts per 10(4)) values show large positive and negativ...
متن کاملEarly (≥4.5 Ga) formation of terrestrial crust: Lu–Hf, δO, and Ti thermometry results for Hadean zircons
Large deviations in ɛHf(T) from bulk silicate Earth seen in N4 Ga detrital zircons from Jack Hills, Western Australia, have been interpreted as reflecting a major differentiation of the silicate Earth at 4.4 to 4.5 Ga. We have expanded the characterization of Hf/Hf initial ratios (Hf ) in Hadean zircons by acquiring a further 116 laser ablation Lu–Hf measurements on 87 grains with ion microprob...
متن کاملThe Hadean Crust: Evidence from >4 Ga Zircons
A review of continental growth models leaves open the possibilities that Earth during the Hadean Eon (∼4.5–4.0 Ga) was characterized by massive early crust or essentially none at all. Without support from the rock record, our understanding of pre-Archean continental crust must largely come from investigating Hadean detrital zircons. We know that these ancient zircons yield relatively low crysta...
متن کاملPlate-tectonic evolution of the Earth: bottom-up and top-down mantle circulation
Intense devolatilization and chemical-density differentiation attended accretion of planetesimals on the primordial Earth. These processes gradually abated after cooling and solidification of an early magma ocean. By 4.3 or 4.2 Ga, water oceans were present, so surface temperatures had fallen far below lowpressure solidi of dry peridotite, basalt, and granite, ~1300, ~1120, and ~950 °C, respect...
متن کاملOxygen isotope ratios and rare earth elements in 3.3 to 4.4 Ga zircons: Ion microprobe evidence for high O continental crust and oceans in the Early Archean
Ion microprobe analyses of oxygen isotope ratios in Early Archean (Hadean) zircons (4.0to 4.4-Ga) reveal variable magmatic O values, including some that are high relative to the mantle, suggesting interaction between magmas and already-formed continental crust during the first 500 million yr of Earth’s history. The high average O value of these zircons is confirmed by conventional analysis. A m...
متن کاملذخیره در منابع من
با ذخیره ی این منبع در منابع من، دسترسی به آن را برای استفاده های بعدی آسان تر کنید
برای دانلود متن کامل این مقاله و بیش از 32 میلیون مقاله دیگر ابتدا ثبت نام کنید
ثبت ناماگر عضو سایت هستید لطفا وارد حساب کاربری خود شوید
ورودعنوان ژورنال:
- Science
دوره 312 5777 شماره
صفحات -
تاریخ انتشار 2006