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Key date in icing over of Antarctica established
THE moment the Pacific and Atlantic oceans linked up, ultimately leading to the freezing of Antarctica, has been traced to 41 million years ago, according to a study of the seabed off the tip of South America.
Howie Scher, at the University of Rochester in New York, and Ellen Martin, of the University of Florida, analysed tiny fish teeth from the bottom of the seabed in the 400-mile-wide Drake Passage, which separates South America from the Antarctic. By looking at the “chemical fingerprints” of the ocean locked inside the teeth, they found that the two continents moved apart about 7m years before glaciers took hold in the polar region.
Different bodies of water have varying “fingerprints” that depend on the age of the rocks submersed in them, so the scientists could tell which ocean had flowed over the seabed at certain points in time. “The study shows for the first time that the opening of the Drake Passage contributed to the cooling of the Antarctic,” said Prof Scher, whose study appeared in the journal Science.
“Once the passage was opened, ice sheets were formed. A ring of cold water was able to form around the continent, which effectively isolated the Antarctic from the rest of the global circulation, so it became colder and colder.” The two continents moved apart over millions of years, with the passage of water between them becoming deeper over time.
There are no significant land masses on the same latitude as the Drake Passage, so the ring of cold water, known as the Antarctic circumpolar current, can flow unimpeded around the continent. “This is the only place in the world where this can happen,” said Prof Martin. “It is an amazing current; it just sits there and stirs.”
Undermining climate action
Britain's scientists are drawing up a plan to fight renewed attempts by sceptics and industry-funded lobby groups to derail international action on climate change. According to a confidential internal memo, the Royal Society expects "groups and individuals" to question the science of global warming and the need to cut greenhouse gas emissions.
It predicts that lobbyists will try to undermine a report next year from the UN's Intergovernmental Panel on Climate Change (IPCC), which is expected to give a new warning on climate change.
Sources say the report, a draft of which was handed to governments earlier this month, will warn that global warming could drive the Earth's temperature to levels far higher than previously predicted. The report draws together research over the past five years and will be made public in February.
The Royal Society memo says: "It seems likely that these groups will again seek to undermine the IPCC in the period around publication. There are already signs these groups will be targeting European countries and Canada to seek to provoke opposition to the Kyoto protocol."
The document says the oil company Exxon Mobil has tried "to influence public opinion about the threat of climate change". It also says "concerted efforts" were made in 2004-05 to change the way the UK media covered climate science after Tony Blair declared that global warming was one of his priorities.
But the memo also criticises environmental campaigners for misrepresenting scientific evidence and says that green groups and the British media "have been guilty of expressing unjustified certainty about the science of climate change".
Hips on fossil snake
A superbly preserved fossil snake with hips and back legs suggests that the reptiles evolved from burrowing land dwellers that lost their legs. The 90m- to 92m-year-old fossil, from Patagonia, puts to rest the argument among palaeontologists over whether the group evolved on land or from primitive sea monsters.
“It is a spectacular find for its age and detail,” said Harry Greene, an expert on snake evolution at Cornell University. “It does bolster the case for [primitive] snakes being terrestrial or subterranean rather than marine.”
The idea that snakes had an aquatic beginning was first put forward by the Victorian fossil hunter Edward Cope. He thought they were most closely related to an extinct group of marine lizards called mosasaurs — ancestors of modern-day monitor lizards.
These began as small coastal-dwelling animals in the early Cretaceous period around 144m years ago, but evolved into fearsome sea monsters, says Olivier Rieppel, an expert on snake evolution at the University of Chicago.
“As the Cretaceous went on they became creatures of the open sea,” he said. “They became very large, they transformed their limbs to flippers and some of them reached 12 metres long.”
Sleep boosts memory
Brain scans have revealed how information we learn during the day is squirrelled away into long-term memory while we sleep. During a good night's rest, memories of recent events are shifted from one part of the brain to another, a process that is crucial for developing long-term memories, according to a report published in the journal Proceedings of the National Academy of Sciences.
The researchers, lead by Dr Philippe Peigneux at the University of Liege in Belgium, gave two teams the task of learning their way around a virtual 3D town by training them on a computer. Using functional magnetic resonance imaging (fMRI), which can take repeated snapshots of activity in the brain, they witnessed people's memories of how to navigate being transferred from a region of the brain that deals with remembering directions, the hippocampus, to a part that governs how we move, the striatum.
One of the teams was then told to stay awake all night, playing video games. Two days later, both groups were again given brain scans, and the scans showed that the group which had rested well was using a different part of the brain to navigate around the virtual town, the striatum.
— Dawn/The Guardian News Service
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