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To: E. Charters who wrote (61368)	9/26/2008 2:51:12 PM
From: marcos	1 Recommendation Read Replies (1) \| Respond to of 78418

Rocks May Be Oldest on Earth, Scientists Say By KENNETH CHANG Published: September 25, 2008 A swath of bedrock in northern Quebec may be the oldest known piece of the Earth’s crust. Researchers report that this rock is 4.28 billion years old and formed when the Earth was less than 300 million years old. In an article appearing in Friday’s issue of the journal Science, scientists report that portions of that bedrock are 4.28 billion years old, formed when the Earth was less than 300 million years old. “These rocks paint this picture of an early Earth that looked pretty much like the modern Earth,” said Richard Carlson of the Carnegie Institution of Washington and one of the authors of the paper. Other scientists are intrigued, but not yet entirely convinced that the rocks are quite that old. “There is a certain amount of healthy skepticism that needs to play a role here,” said Stephen J. Mojzsis, a professor of geological sciences at the University of Colorado. Dr. Mojzsis said the new research was well done, but that he thought these were younger sedimentary rocks, pressed together out of the remnants of earlier rocks that were indeed 4.28 billion years old. “I hope that I’m wrong,” Dr. Mojzsis said. “If that happens, I believe there will be a land rush by geologists to northern Quebec.” At present, the oldest dated rocks are in the Canadian Northwest, at 4.03 billion years old. Geologists have also found older bits of the Earth: tiny, hardy crystals known as zircons, as old as 4.36 billion years old, embedded within younger rocks in Western Australia. The age of the Earth is more than 4.5 billion years. Radioactive elements trapped within zircons provide precise ages, but Dr. Carlson and his collaborators at McGill University and the University of Quebec have not found any zircons in the Quebec bedrock so far. Instead, they determined the age of the rocks from the amounts of neodymium and samarium, two rare earth elements. Dr. Carlson saidthe skeptics might be correct and the bedrock could be younger rocks that formed out of older material. “The age is pretty certain,” he said. “The interpretation of the age is less certain.” If the rocks are as old as claimed, what is significant would be that “They’re not dramatically different from rocks you would find today in Japan or places like that,” Dr. Carlson said. In fact, their chemical signature looks most similar to ocean floor that has been pulled under continents, Dr. Carlson said. That suggests that the process of plate tectonics, reshaping and moving continents, could have already started on the very early Earth. At the very least, the existence of solid rock 4.28 billion years ago would run counter to the traditional image of the young Earth as a roiling cauldron of magma oceans, a view that is falling by the wayside among researchers as more geological data is unearthed. nytimes.com