Document Detail


Tracing the stepwise oxygenation of the Proterozoic ocean.
MedLine Citation:
PMID:  18368114     Owner:  NLM     Status:  MEDLINE    
Abstract/OtherAbstract:
Biogeochemical signatures preserved in ancient sedimentary rocks provide clues to the nature and timing of the oxygenation of the Earth's atmosphere. Geochemical data suggest that oxygenation proceeded in two broad steps near the beginning and end of the Proterozoic eon (2,500 to 542 million years ago). The oxidation state of the Proterozoic ocean between these two steps and the timing of deep-ocean oxygenation have important implications for the evolutionary course of life on Earth but remain poorly known. Here we present a new perspective on ocean oxygenation based on the authigenic accumulation of the redox-sensitive transition element molybdenum in sulphidic black shales. Accumulation of authigenic molybdenum from sea water is already seen in shales by 2,650 Myr ago; however, the small magnitudes of these enrichments reflect weak or transient sources of dissolved molybdenum before about 2,200 Myr ago, consistent with minimal oxidative weathering of the continents. Enrichments indicative of persistent and vigorous oxidative weathering appear in shales deposited at roughly 2,150 Myr ago, more than 200 million years after the initial rise in atmospheric oxygen. Subsequent expansion of sulphidic conditions after about 1,800 Myr ago (refs 8, 9) maintained a mid-Proterozoic molybdenum reservoir below 20 per cent of the modern inventory, which in turn may have acted as a nutrient feedback limiting the spatiotemporal distribution of euxinic (sulphidic) bottom waters and perhaps the evolutionary and ecological expansion of eukaryotic organisms. By 551 Myr ago, molybdenum contents reflect a greatly expanded oceanic reservoir due to oxygenation of the deep ocean and corresponding decrease in sulphidic conditions in the sediments and water column.
Authors:
C Scott; T W Lyons; A Bekker; Y Shen; S W Poulton; X Chu; A D Anbar
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Publication Detail:
Type:  Historical Article; Journal Article; Research Support, Non-U.S. Gov't; Research Support, U.S. Gov't, Non-P.H.S.    
Journal Detail:
Title:  Nature     Volume:  452     ISSN:  1476-4687     ISO Abbreviation:  Nature     Publication Date:  2008 Mar 
Date Detail:
Created Date:  2008-03-27     Completed Date:  2008-04-30     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  0410462     Medline TA:  Nature     Country:  England    
Other Details:
Languages:  eng     Pagination:  456-9     Citation Subset:  IM    
Affiliation:
Department of Earth Sciences, University of California, Riverside, California 92521, USA. cscot002@ucr.edu
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MeSH Terms
Descriptor/Qualifier:
Atmosphere / chemistry
Geologic Sediments / chemistry
History, Ancient
Molybdenum / analysis
Oceans and Seas
Oxygen / analysis*,  chemistry
Seawater / chemistry*
Sulfides / chemistry
Time Factors
Chemical
Reg. No./Substance:
0/Sulfides; 7439-98-7/Molybdenum; 7782-44-7/Oxygen

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine


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