Did Cooling Oceans Trigger Ordovician Biodiversification? Evidence from Conodont Thermometry
Julie Trotter1, Ian Williams1, Chris Barnes2, Christophe Lécuyer3 and Robert Nicoll1
1 Research School of Earth Sciences, Australian
National University, Canberra, ACT 0200, Australia
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 in situ ion microprobe (SHRIMP) 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 favourable climate regime not only implies that the oxygen isotopic composition of Ordovician seawater was similar to today, but that climate played an overarching role in promoting the unprecedented increases in biodiversity that characterized this period.