Currents


Fossil evidence tells of Arctic warming

Immediately after volcanoes around the world spewed carbon dioxide into the atmosphere about 90 million years ago, the Arctic was as warm as present-day Florida, according to fossil evidence discovered by a College team in the high Canadian Arctic. The fossils indicate that at least once in Earth's history, high amounts of the greenhouse gas warmed Earth to much higher temperatures than usual.

The find of bones from several crocodile-like beasts known as champsosaurs, along with turtles and fish--champsosaurs' favorite foods--is detailed in the December 18 issue of Science. Analysis of the find was done by the Rochester team in collaboration with researchers from the Royal Tyrrell Museum of Paleontology in Drumheller, Alberta; the Berkeley Geochronology Center; and the Scripps Institution of Oceanography in San Diego.

The highlight of the find is bones that belonged to an eight-foot champsosaur, a now-extinct crocodile-like beast. The team found the bones in rocks scattered over a period of time ranging from several hundred thousand to a few million years. The reptiles, which were tied to their freshwater environment on Axel Heiberg Island, needed an extended warm period each summer to survive and reproduce. Based on the numbers and sizes of the animals found, the team estimates that the annual mean temperature in the Arctic during the late Cretaceous period, from about 92 million to 86 million years ago, was approximately 57 degrees Fahrenheit. That means it was rarely if ever freezing during the winter, and summer temperatures consistently reached into the 80s and 90s.

The bones were discovered by a team of students, including graduate student Rory Cottrell, that was led by John Tarduno, associate professor and chair of the Department of Earth and Environmental Sciences, during an expedition in the summer of 1996. Driven off by heavy rain and snow, the team returned in the summer of 1997 to complete the excavation. The bones come from a layer of sediment right on top of 1,000 feet of hardened lava, known as basalt, and below a layer of marine rock common in the Arctic. That dates the fossils to the period immediately after the volcanism ended.

"I had been looking for rocks from this layer for many years--in most places the layer doesn't exist or has worn away," said Tarduno, a geophysicist who studies Earth's magnetic field. "We were walking along a ridge, and we spotted a layer between the brown volcanic rocks and the black marine shale. From a distance we knew that these rocks represented an environment we hadn't seen before. ... It was one of those rare instances where you know immediately that what you're looking at has tremendous importance."

Scientists have long considered the Cretaceous period, which lasted from 144 million to 65 million years ago, a warm time period and a possible model of the greenhouse effect. That model has come under closer scrutiny recently as some scientists have suggested that the late Cretaceous period was actually a cool time. The new evidence indicates that time period may be an even better model of global warming than scientists thought.

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