Eras

Extinctions Caused by the Ice that Burns

Rice University researchers calculated that enough methane may have been stored under the sea to cause the Paleocene-Eocene Thermal Maximum 56 millionyears ago. Clockwise from top left: chemical engineer George Hirasaki, Earth scientist Gerald Dickens, chemical engineer Walter Chapman and graduate student Guangsheng Gu, coauthors of a new paper inNature Geoscience. Credit: Jeff Fitlow/Rice University The release of massive amounts of carbon from methane hydrate frozen under the seafloor 56 million years ago has been linked to the greatest changein global climate since a dinosaur-killing asteroid presumably hit Earth 9 million years earlier. New calculations by researchers at Rice University show that this long-controversial scenario is quitepossible. Nobody knows for sure what started the incident, but there's no doubt Earth's temperature rose by as much as 6 degrees Celsius. That affected the planet for up to 150,000 years, until excesscarbon in the oceans and atmosphere was reabsorbed into sediment. Earth's ecosystem changed and many species went extinct during the Paleocene-Eocene Thermal Maximum (PETM) 56 million years ago, whenat least 2,500 gigatonnes of carbon, eventually in the form of carbon dioxide, were released into the ocean and atmosphere. (The era is described in great detail in a recent National Geographicfeature.) A new report by Rice scientists in Nature Geoscience suggests that at the time, even though methane-containing gas hydrates – the "ice that burns" – occupied only a small zone of sediment underthe seabed before the PETM, there could have been as much stored then as there is now. This is a concern to those who believe the continued burning of fossil fuels by humans could someday triggeranother feedback loop that disturbs the stability of methane hydrate under the ocean and in permafrost; this change could warm the atmosphere and prompt the release of large amounts of methane, a more...