Forests made the world frigid?Forests made the world frigid? It's easy to imagine how ice ages may have affected life as itevolved. But some scientists are beginning to suspect that, conversely, changes in the distribution and diversity of species may also have changed the climate. James C. G. Walker at the University of Michigan (body, education) University of Michigan - A large cosmopolitan university in the Midwest USA. Over 50000 students are enrolled at the University of Michigan's three campuses. The students come from 50 states and over 100 foreign countries. in Ann Arborand Andrew H. Knoll Andrew H. Knoll is the Fisher Professor of Natural History and a Professor of Earth and Planetary Sciences at Harvard University. He is best known for his work on Precambrian microfossils and using stable isotopes for stratigraphic correlation, but has longstanding interests in at Harvard University Harvard University, mainly at Cambridge, Mass., including Harvard College, the oldest American college. Harvard College Harvard College, originally for men, was founded in 1636 with a grant from the General Court of the Massachusetts Bay Colony. have concluded on the basis of biogeochemical modeling that one glacial episode 290 million years ago was triggered by the spread of forests onto land, as adaptations enabled plants to live and reproduce without the constant presence of water. The researchers reason that the earth cooled because the forests removed atmospheric carbon dioxide carbon dioxide, chemical compound, CO2, a colorless, odorless, tasteless gas that is about one and one-half times as dense as air under ordinary conditions of temperature and pressure. - a "greenhouse" gas that helps prevent the earth's heat from escaping to space. The plants converted the carbon to organic matter, which was then buried in sediments. "The notion that glacial epochs could be due to changes inCO.sub.2 is an old idea," says Walker. "Only recently have we begun to have enough information on global geochemical cycles to figure out what might cause CO.sub.2 concentrations to change." Scientists think continental configurations influence ice ages as well. Having a lot of land near the poles, for example, might allow a buildup of glacial snow and ice. Walker and Knoll's model indicates that the burial of carbonwas also key to the onset of two other glacial epochs, one at 700 million years ago and the other at about 2 million years ago. But Walker thinks these ice ages were triggered by tectonics and not biology. Strontium strontium (strŏn`shēəm) [from Strontian, a Scottish town], a metallic chemical element; symbol Sr; at. no. 38; at. wt. 87.62; m.p. 769°C;; b.p. 1,384°C;; sp. gr. 2.6 at 20°C;; valence +2. isotope levels in rocks suggest that volcanic activity or seafloor spreading seafloor spreading, theory of lithospheric evolution that holds that the ocean floors are spreading outward from vast underwater ridges. First proposed in the early 1960s by the American geologist Harry H. was enhanced during those epochs. These processes, he proposes, drew oxygen out of the oceans and atmosphere so that more organic carbon was preserved in sediments and not returned to the atmosphere by respiring organisms. |
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