- 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 University of Rochester 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.
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- The find of bones from several crocodile-like
beasts known as champsosaurs, along with turtles and fish - champsosaurs'
favorite foods - is detailed in the Dec. 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.
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- The highlight of the find are bones that
belonged to an eight-foot champsosaur, a now-extinct crocodile-like beast
with a long snout and razor-sharp teeth. The team found bones from several
champsosaurs, as well as fish and turtles, in rocks scattered over several
hundred thousand to a few million years.
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- 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 about 57 degrees Fahrenheit. That means it
was rarely if ever freezing during the winter, and summer temperatures
consistently reached into the 80s and 90s.
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- The bones were discovered by a University
team of students led by Professor John Tarduno 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.
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- "I had been looking for rocks from
this layer for many years - in most places the layer doesn't exist or has
worn away," says 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.
Once we reached them, we realized these were fine- grain sedimentary rocks
ideal for preservation of fossils, and I bet the students we'd find fossils.
Within five minutes one of my students pulled up a femur and said, "Like
this?"
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- "It was one of those rare instances
where you know immediately that what you're looking at has tremendous importance.
It was clearly a vertebrate fossil - our guess was a large reptile, which
would have required a relatively warm climate to survive."
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- The fossils locked in a record of what
was happening in the Arctic just as extreme volcanism around the planet
was winding down. Most of the volcanic activity didn't resemble spectacular
eruptions like Mt. Pinatubo. Instead, the eruptions were "basaltic"
- tons of lava oozed out, and carbon dioxide floated skyward. Besides huge
amounts of lava in the Arctic, where hardened lava rock today measures
more than a kilometer thick in some places, magma oozed from volcanoes
in the Caribbean, in the Pacific Ocean northeast of Australia, in the Indian
Ocean, off the coasts of Madagascar and Brazil, in South Africa and in
the Southwestern United States.
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- 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, where gases like
carbon dioxide collect in the atmosphere and trap in heat, causing global
warming. Understanding how warming happened in the past helps scientists
predict how our planet might react in the future to the increased CO2 being
pumped into the atmosphere from car exhaust, coal plants, and other burning
of fossil fuels. That model has come under closer scrutiny recently as
some scientists have suggested that the late Cretaceous was actually a
cool time. The new evidence indicates that the late Cretaceous may be an
even better model of global warming than scientists thought.
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- "We can't avoid the fact that these
fossils are sitting right on top of this extremely large volcanic eruption,"
says Tarduno. "And if you look around the world, it was an unusually
active time, with many eruptions occurring at the same time. It's very
reasonable to suggest that so much CO2 was dumped into the atmosphere that
it overwhelmed the system, causing global warming."
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- Scientists have long known that at times
in the past the Arctic was much warmer than it is today. One piece of evidence
is the many fossil trees in the Arctic; today the nearest living tree is
about 1,000 miles away. But no one has found hard evidence before for such
warm temperatures. "This will be a puzzle for people who model climate,"
says Tarduno, "but the fossils, together with the radiometric dating,
provide very hard evidence of extremely warm temperatures in the Arctic."
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- The bones the team found come from what
was likely a freshwater bay on Axel Heiberg Island in the high Canadian
Arctic, at 79 degrees latitude. During the Cretaceous the island was a
bit south of where it is today but was still well within the Arctic Circle.
The two dozen bones the team found include a tibia, a femur, and ribs and
vertebrae from both small and large champsosaurs, as well as turtle shells
and several bones from fish. All came from a sediment about 12 feet thick
running for several hundred feet along the Dragon River.
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- Analyzing the rocks and fossils were
Tarduno; paleontologist Donald Brinkman of the Royal Tyrrell Museum of
Paleontology of Canada in Drumheller, Alberta; Paul Renne, director of
the Berkeley Geochronology Center, who did the isotope dating of the rocks;
and Pat Castillo of Scripps Institute of Oceanography in San Diego, who
chose which rocks to date. The project was funded by the National Science
Foundation.
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- Also taking part in the research were
several University of Rochester students, including undergraduate Howard
Scher and graduate student Rory Cottrell. The find came thanks to the perseverance
of the students and Tarduno, who spent six weeks during both summers traipsing
through knee-deep snow, huddling in nylon tents flapping in strong winds,
and enduring 24 hours of sunshine each day, all to find and excavate just
the right rocks. Dubbing their tent city 700 miles from the North Pole
the "Polar Hotel" after the tents they slept in, the students
were among the first humans to explore some sections of the mountainous,
rocky part of the Arctic.
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- Experiences like this are plentiful at
the University, where faculty both conduct world-class research and teach
small classes of students. Like Scher, about half the University's undergraduates
work closely with professors on independent research projects. The Department
of Earth and Environmental Sciences is known nationwide for the dozens
of students it equips with extensive field experience and graduates each
year.
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- The original news release can be found
at <http://www.rochester.edu/pr/releases/ear/champ.htmhttp://www.rochester.edu/pr/
releases/ear/champ.htm
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