Silicon Isotope Evidence Against an Enstatite Chondrite Earth

Science ◽  
2012 ◽  
Vol 335 (6075) ◽  
pp. 1477-1480 ◽  
Author(s):  
C. Fitoussi ◽  
B. Bourdon
Keyword(s):  
Silicon Isotope ◽  
Isotope Evidence ◽  
Enstatite Chondrite

The Role of Diagenesis in the Apparent Rise of Diatoms

2021 ◽  
Author(s):  
Sophie Westacott ◽  
Noah Planavsky ◽  
Ming-Yu Zhao ◽  
Pincelli Hull
Keyword(s):  
Silicon Isotope ◽  
Sedimentation Rates ◽  
Bottom Water Temperature ◽  
Baleen Whales ◽  
The Past ◽  
Isotope Evidence ◽  
Silica Cycle ◽  
Fossil Data ◽  
Burial Efficiency

<p><span>Diatoms are one of the most dominant primary producers in the ocean today and largely control the modern marine silica cycle. Their ecological expansion in the Cenozoic is thought to have lowered silica concentrations by two orders of magnitude and has been linked to the rise of grasslands and baleen whales. According to the fossil record much of diatoms' rise to dominance occurred in the past 20 m.y.; however, silicon isotope evidence suggests an earlier expansion. Using a diagenetic model and collated deep sea drill core data, we examine how changes in bottom-water temperature and sedimentation rates over the past 65 m.y. affected the burial efficiency of biogenic silica. We find that once taphonomic potential is taken into account there is no support for the traditionally recognized ~5-20 Ma increase in diatom abundance. These results help reconcile interpretations based on geochemical and fossil data, and add to mounting evidence pushing back the evolution of the modern silica cycle to before 20 Ma and possibly earlier than 40 Ma.</span></p>

Chromium Stable Isotope Panorama of Chondrites and Implications for Earth Early Accretion

2021 ◽  
Vol 923 (1) ◽  
pp. 94
Author(s):  
Ke Zhu ◽  
Frédéric Moynier ◽  
Conel M. O’D. Alexander ◽  
Jemma Davidson ◽  
Devin L. Schrader ◽  
...  
Keyword(s):  
Stable Isotope ◽  
Isotopic Composition ◽  
Isotope Composition ◽  
Acid Leaching ◽  
Building Blocks ◽  
Silicon Isotope ◽  
Stable Isotope Fractionation ◽  
Two Samples ◽  
Enstatite Chondrite ◽  
Enstatite Chondrites

Abstract We investigated the stable isotope fractionation of chromium (Cr) for a panorama of chondrites, including EH and EL enstatite chondrites and their chondrules and different phases (by acid leaching). We observed that chondrites have heterogeneous δ 53Cr values (per mil deviation of the 53Cr/52Cr from the NIST SRM 979 standard), which we suggest reflect different physical conditions in the different chondrite accretion regions. Chondrules from a primitive EH3 chondrite (SAH 97096) possess isotopically heavier Cr relative to their host bulk chondrite, which may be caused by Cr evaporation in a reduced chondrule-forming region of the protoplanetary disk. Enstatite chondrites show a range of bulk δ 53Cr values that likely result from variable mixing of isotopically different sulfide-silicate-metal phases. The bulk silicate Earth (δ 53Cr = –0.12 ± 0.02‰, 2SE) has a lighter Cr stable isotope composition compared to the average δ 53Cr value of enstatite chondrites (–0.05 ± 0.02‰, 2SE, when two samples out of 19 are excluded). If the bulk Earth originally had a Cr isotopic composition that was similar to the average enstatite chondrites, this Cr isotope difference may be caused by evaporation under equilibrium conditions from magma oceans on Earth or its planetesimal building blocks, as previously suggested to explain the magnesium and silicon isotope differences between Earth and enstatite chondrites. Alternatively, chemical differences between Earth and enstatite chondrite can result from thermal processes in the solar nebula and the enstatite chondrite-Earth, which would also have changed the Cr isotopic composition of Earth and enstatite chondrite parent body precursors.

CALCIUM ISOTOPE EVIDENCE OF AN EPISODE OF OCEAN ACIDIFICATION ACROSS THE SMITHIAN-SPATHIAN BOUNDARY

2018 ◽  
Author(s):  
He Zhao ◽  
◽  
Feifei Zhang ◽  
Thomas J. Algeo ◽  
Zhong Qiang Chen ◽  
...  
Keyword(s):  
Ocean Acidification ◽  
Calcium Isotope ◽  
Isotope Evidence
Sign in / Sign up

Export Citation Format

Share Document