By Natalie Wolchover
On a 1987 voyage to the Antarctic, the paleoceanographer James Kennett and his crew dropped anchor in the Weddell Sea, drilled into the seabed, and extracted a vertical cylinder of sediment. In an inch-thick layer of plankton fossils and other detritus buried more than 500 feet deep, they found a disturbing clue about the planet’s past that could spell disaster for the future.
Lower in the sediment core, fossils abounded from 60 plankton species. But in that thin cross-section from about 56 million years ago, the number of species dropped to 17. And the planktons’ oxygen and carbon isotope compositions had dramatically changed. Kennett and his student Lowell Stott deduced from the anomalous isotopes that carbon dioxide had flooded the air, causing the ocean to rapidly acidify and heat up, in a process similar to what we are seeing today.
While those 17 kinds of plankton were sinking through the warming waters and settling on the Antarctic seabed, a tapir-like creature died in what is now Wyoming, depositing a tooth in a bright-red layer of sedimentary rock coursing through the badlands of the Bighorn Basin. In 1992, the finder of the tooth fossil, Phil Gingerich, and collaborators Jim Zachos and Paul Koch reported the same isotope anomalies in its enamel that Kennett and Stott had presented in their ocean findings a year earlier. The prehistoric mammal had also been breathing CO2-flooded air.
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