A new technique has allowed scientists to pin down the timing of ancient glaciations, linking them more firmly to two bursts of extinction.
A team of researchers, including earth and planetary scientists from Washington University in St. Louis, for the first time has been able to reconstruct both ocean temperature and general ice thickness of massive glaciers during one of the biggest mass extinctions in history hundreds of millions of years ago.
The extinction, which occurred between 445 and 443 million years ago in the Late Ordovician Period, is one of the five biggest mass extinctions in Earth history, wiping out an estimated 75 percent of simple marine species.
The Ordovician glaciation is the only one that coincides with a major mass marine extinction. Shedding light on this ancient event can help reveal clues about the interplay between evolution, climate and environment.
David Fike, PhD, Washington University assistant professor of earth and planetary sciences in Arts & Sciences, along with his post-doctoral researcher David Jones, PhD, and colleagues from the California Institute of Technology (Caltech), gathered carbonate rock samples from the Quebec, Canada area and east-central Missouri that date back to the Late Ordovician, when all of the present mid-continental United States was a shallow ocean.
David Fike, PhD, assistant professor of earth and planetary sciences, holds a 443-million-year-old slab of Ordovician limestone from Anticosti Island in Quebec that is sprinkled with the fossilized remains of marine creatures killed during a cooling pulse. Work he and his colleagues did using a new paleothermometer recently linked a double cooling pulse at the end of the Ordovician period to a double mass exintinction in ancient oceans.
They used mass spectroscopy to analyze the chemistry of the fossilized marine animal shells in the carbonates and plied a new type of “paleothermometer,” developed by John Eiler, PhD, of Caltech, to determine the average temperatures of the Late Ordovician oceans.
Eiler’s technique measures the extent to which heavy isotopes of carbon and oxygen bond to one another in the carbonate (CO,-) portion of ancient limestone rather than to the sea of light isotopes in which they swim. The proportion of these heavy-isotope bonds is sensitive to the temperature at which the rock formed; the lower the temperature, the greater the clumping. Clumping thus forms the basis for a simple paleothermometer that can be used to take the temperature of ancient climates.