Debate smolders over cause of ice ages.During the last 2 million years, Earth has endured more than 20 Ice ages of various lengths. The standard explanation for these periodic freezes involves rhythmic variations in the planet's orbit and tilt, but this theory has come under fire in recent years from researchers studying a Nevada cave called Devils Hole (SN: 10/10/92, p. 228). Now, a team of scientists contends that their findings have exorcised the specter of Devils Hole by confirming the orbital theory. The debate centers on the timing of the last interglacial in·ter·gla·cial adj. Occurring between glacial epochs. n. A comparatively short period of warmth during an overall period of glaciation. period, the short warm spell Warm Spell (1988-1994) was an American Eclipse Award winning thoroughbred racehorse, a Kentucky-bred son of Northern Baby, owned and trained by John K. Griggs and bred by Robert Kluener. He was ridden primarily by the owner/trainer's son, Kirk Griggs. sandwiched between the last ice age and the next-to-last one. Dating of calcium carbonate calcium carbonate, CaCO3, white chemical compound that is the most common nonsiliceous mineral. It occurs in two crystal forms: calcite, which is hexagonal, and aragonite, which is rhombohedral. layers in Devils Hole suggests that the last interglacial started more than 150,000 years ago--a time that doesn't fit the orbital hypothesis. Summer sunlight then was not strong enough to melt the giant ice caps and end the glacial epoch. R. Lawrence Edwards of the University of Minnesota (body, education) University of Minnesota - The home of Gopher. http://umn.edu/. Address: Minneapolis, Minnesota, USA. in Minneapolis and his colleagues attacked the problem with a dramatically improved version of an old dating technique that relies on the radioactive decay radioactive decay n. 1. Spontaneous disintegration of a radionuclide accompanied by the emission of ionizing radiation in the form of alpha or beta particles or gamma rays. 2. An instance of such disintegration. of uranium-235 to protactinium protactinium (prō'tăktĭn`ēəm), radioactive chemical element; symbol Pa; at. no. 91; at. wt. 231.0359; m.p. greater than 1,600°C;; b.p. 4,026°C;; sp. gr. 15.37 (calculated); valence +4, +5. 231. They rechecked the ages of previously dated coral from Barbados that grew during the last interglacial, when Earth was warm and sea levels were higher than they are today. The new coral dates confirm that sea levels were high 126,000 to 121,000 years ago, when summer sunlight grew most intense in the far northern latitudes, the scientists report in the May 2 Science. These results, they argue, back up the orbital explanation of the ice ages. That conclusion gets a cold reception from Isaac J. Winograd, a researcher at the U.S. Geological Survey in Reston, Va. Winograd lauds Lauds is one of the two "major hours" in the Roman Catholic Liturgy of the Hours. It is to be recited in the early morning hours, preferably near dawn. Structure of the hour the protactinium, dating technique but objects that the new study reanalyzed coral samples already known to support the orbital hypothesis. To address the issue thoroughly, says Winograd, Edwards should redate other corals that show sea levels rising far earlier or later than orbital theory would predict. |
|
||||||||||||||||||||
Printer friendly
Cite/link
Email
Feedback
Reader Opinion