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Multiple chondritic meteorite fragments have been found in two sedimentary rock samples from an end-Permian bed at Graphite Peak in Antarctica. The Ni/Fe, Co/Ni, and P/Fe ratios in metal grains; the Fe/Mg and Mn/Fe ratios in olivine and pyroxene; and the chemistry of Fe-, Ni-, P-, and S-bearing oxide in the meteorite fragments are typical of CM-type chondritic meteorites. In one sample, the meteoritic fragments are accompanied by more abundant discrete metal grains, which are also found in an end-Permian bed at Meishan, southern China. We discuss the implications of this finding for a suggested global impact event at the Permian-Triassic boundary., Meteorite samples that occur as fragments in Earth rocks are rare. There are only a few examples in the literature of which two are deep-sea drill core occurrences. One includes [...]

Author(s): Cin-Ty Lee (corresponding author) [1, 2]; Qingzhu Yin [1]; Roberta L. Rudnick [1, 2]; Stein B. Jacobsen [1] Stable continental regions, free from tectonic activity, are generally found only [...]

Author(s): Kun Wang (corresponding author) [1, 2]; Stein B. Jacobsen [1] The EarthMoon system has unique chemical and isotopic signatures compared with other planetary bodies [1, 2, 3]; any successful [...]

Earth probably accreted in two stages corresponding to conditions before and after the removal of gas from the nebular disk. Helium and neon in the mantle primarily record a solarlike component likely incorporated during the first stage by solution into a magma ocean blanketed under a massive protoatmosphere of molecular hydrogen and helium. The heavier noble gases primarily reflect a meteoritic (planetary) component trapped in accreted planetesimals. This model provides a possible explanation for the reduced and oxidized accretion stages inferred from siderophile elements and may explain why the present mantle appears to be too oxidized to be in equilibrium with the core., Planets form from material left behind in residual accretion disks once infall of the collapsing source clouds is complete. Such disks experience a two-stage history involving the separation of minor [...]

Carbonate-rich sedimentary rocks of the western Anabar region, northern Siberia, preserve an exceptional record of evolutionary and biogeochemical events near the Proterozoic/Cambrian boundary. Sedimentologically, the boundary succession can be divided into three sequences representing successive episodes of late transgressive to early highstand deposition; four parasequences are recognized in the sequence corresponding lithostratigraphically to the Manykai Formation. Small shelly fossils are abundant and include many taxa that also occur in standard sections of southeastern Siberia. Despite this coincidence of faunal elements, biostratigraphic correlations between the two regions have been controversial because numerous species that first appear at or immediately above the basal Tommotian boundary in southeastern sections have first appearances scattered through more than thirty metres of section in the western Anabar. Carbon- and Sr-isotopic data on petrographically and geochemically screened samples collected at one- to two-metre intervals in a section along the Kotuikan River, favour correlation of the Staraya Reckha Formation and most of the overlying Manykai Formation with sub-Tommotian carbonates in southeastern Siberia. In contrast, isotopic data suggest that the uppermost Manykai Formation and the basal 26 m of the unconformably overlying Medvezhya Formation may have no equivalent in the southeast; they appear to provide a sedimentary and palaeontological record of an evolutionarily significant time interval represented in southeastern Siberia only by the sub-Tommotian unconformity. Correlations with radiometrically dated horizons in the Olenek and Kharaulakh regions of northern Siberia suggest that this interval lasted approximately three to six million years, during which essentially all 'basal Tommotian' small shelly fossils evolved.

Sm-Nd isotopic analysis of garnet reveals two amphibolite metamorphic periods with a difference of 16 million years. Sm-Nd comprises hornblende, garnet, plagioclase and apatite and reveals mineral growth at a metamorphic peak. The garnet contains inclusion-filled and inclusion-free fragments with three age periods.

It has been thought that the Earth remained undifferentiated until 4.5 billion years ago, when the crust was thought to have started growing. But the isotope ratio of neodymium indicates that by 3.8 billion years ago 40% of the present crust had formed. This fact, together with an analysis of the ratio of samarium 147 to neodymium 143, suggests that the Earth began differentiating about 4.5 billion years ago.

We suggest that a buried 180-km-diameter circular structure on the Yucatan Peninsula, Mexico, is an impact crater. Its size and shape are revealed by magnetic and gravity-field anomalies, as well as by oil wells drilled inside and near the structure. The stratigraphy of the crater includes a sequence of andesitic igneous rocks and glass interbedded with, and overlain by, breccias that contain evidence of shock metamorphism. The andesitic rocks have chemical and isotopic compositions similar to those of tektites found in Cretaceous/Tertiary (K/T) ejecta. A 90-m-thick K/T boundary breccia, also containing evidence of shock metamorphism, is present 50 km outside the crater's edge. This breccia probably represents the crater's ejecta blanket. The age of the crater is not precisely known, but a K/T boundary age is indicated. Because the crater is in a thick carbonate sequence, shock-produced [CO.sub.2] from the impact may have caused a severe greenhouse warming.

Author(s): Stein B. Jacobsen (corresponding author) Unlike Earth, several bodies such as the Moon, Mercury and Mars have a clear record of their surface history dating back almost to the [...]

Author(s): Qingzhu Yin [1]; Stein B. Jacobsen (corresponding author) [1]; Katsuyuki Yamashita [1, 2] Variations in the isotopic composition of some components in primitive meteorites demonstrate that the pre-solar material [...]

Author(s): Stein B. Jacobsen (corresponding author) The Earth's harshest glaciations occurred between about 600 million and 800 million years ago, in the late Neoproterozoic era. The severity of the glaciations [...]

The earth has a radiogenic W-isotopic composition compared to chondrites, demonstrating that it formed while Hf was extant in Earth and decaying to W. The Hf-W data for lunar samples can be reconciled with a major moon forming impact that terminated the terrestrial accretion process ~30 Myr after the origin of the solar system.

Strontium concentration and isotopic data for subsurface flowing groundwaters of the Ganges-Brahmaputra (G-B) delta in the Bengal Basin demonstrate that this is a potentially significant source of strontium to the oceans, equal in magnitude to the dissolved strontium concentration carried to the oceans by the G-B river waters. The strontium concentrations of groundwaters are higher by a factor of about 10 than typical G-B river waters and they have similar [sup.87]Sr/[sup.86]Sr ratio to the river waters. These new data suggest that the present contribution of the G-B system to the rise in [sup.87]Sr/[sup.86]Sr ratio in seawater is higher by at least a factor of 2 to 5 than the average over the past 40 million years., Variations of [sup.87]Sr/[sup.86]Sr ratio in seawater are primarily due to variations in continental erosion rates as well as variations in the Sr isotopic composition of this input to the oceans [...]

Thermobarometric and Os isotopic data for peridotite xenoliths from late Miocene and younger lavas in the Sierra Nevada reveal that the lithospheric mantle is vertically stratified: the shallowest portions ([is less than] 45 to 60 kilometers) are cold (670 ° to 740 ° C) and show evidence for heating and yield Proterozoic Os model ages, whereas the deeper portions (45 to 100 kilometers) yield Phanerozoic Os model ages and show evidence for extensive cooling from temperatures [is greater than] 1100 ° C to 750 ° C. Because a variety of isotopic evidence suggests that the Sierran batholith formed on preexisting Proterozoic lithosphere, most of the original lithospheric mantle appears to have been removed before the late Miocene, leaving only a sliver of ancient mantle beneath the crust., Lithospheric removal, in the form of detachment, foundering, or peeling away of the lithospheric mantle with or without lower crust into the convecting mantle, has been predicted by various geodynamic [...]

Recent reports (1-4) on me tungsten (W) isotope composition of meteorites have led to a completely revised time scale for the formation of the terrestrial planets. The results show that [...]

Author(s): Qing-zhu Yin (corresponding author) [1]; Stein B. Jacobsen [2] Arising from: B. J. Wood & A. N. Halliday Nature 437, 1345-1348 (2005); Wood & Halliday reply Constraining the timing [...]