Did Cooling Oceans Trigger Ordovician Biodiversification? Evidence from Conodont Thermometry
Abstract
The Ordovician Period, long considered a supergreenhouse state, saw one of the greatest radiations of life in Earth's history. Previous temperature estimates of up to ∼70°C have spawned controversial speculation that the oxygen isotopic composition of seawater must have evolved over geological time. We present a very different global climate record determined by ion microprobe oxygen isotope analyses of Early Ordovician–Silurian conodonts. This record shows a steady cooling trend through the Early Ordovician reaching modern equatorial temperatures that were sustained throughout the Middle and Late Ordovician. This favorable climate regime implies not only that the oxygen isotopic composition of Ordovician seawater was similar to that of today, but also that climate played an overarching role in promoting the unprecedented increases in biodiversity that characterized this period.
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The development of SHRIMP in situ oxygen isotope analysis was partly funded by the Australian Research Council (grant DP0559604 to I.S.W.). An Australian Postgraduate Award financed J.A.T.'s Ph.D. conodont geochemistry research, and the Paleontological Society and Mid-American Paleontological Society awarded a student bursary to J.A.T. P. Holden, R. Ickert, and J. Hiess contributed to developing the oxygen isotope analytical procedures. M. McCulloch and B. Webby provided comments that improved the manuscript.
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Science
Volume 321 | Issue 5888
25 July 2008
25 July 2008
Copyright
American Association for the Advancement of Science.
Submission history
Received: 29 January 2008
Accepted: 17 June 2008
Published in print: 25 July 2008
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