Ancient formation shows glacier activity. (Snowball Melting?).Was Earth a solid snowball 700 million years ago? Some geologists have been looking for Looking for In the context of general equities, this describing a buy interest in which a dealer is asked to offer stock, often involving a capital commitment. Antithesis of in touch with. an answer in an ancient, well-preserved glacial formation in the mountains of northern Oman. Their conclusion--that Earth experienced intermittent ice ages like those in Earth's more recent history--weakens the snowball theory. The snowball scenario has Earth freezing several times between 750 and 580 million years ago, during the Neoproterozoic period (SN: 8/29/98, p. 137). Each time, so the theory goes, ice covered all of Earth for about 10 million years, until 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. from volcanoes accumulated and created a greenhouse effect greenhouse effect: see global warming. greenhouse effect Warming of the Earth's surface and lower atmosphere caused by water vapour, carbon dioxide, and other trace gases in the atmosphere. Visible light from the Sun heats the Earth's surface. that thawed the planet. To support the snowball theory, geologists have pointed to sedimentary evidence from the thawing periods. Among this evidence are distinct limestone formations found worldwide on top of Neoproterozoic sediments. These so-called cap carbonates, which only form in warm seas and contain few signs of past life from the prior frozen period, represent Earth's abrupt transition from a snowball to a greenhouse Earth, some scientists have argued. But now geologists have looked under cap carbonates to examine the glacial sediments directly. They've studied sediments in Oman's Fiq Member, a formation that is 1.5 kilometers thick and exposed across 50 km of sparsely vegetated terrain. "We were able to really work out the anatomy of this particular glacial deposit," says Philip A. Allen, a geologist at the Swiss Federal Institute of Technology The Swiss Federal Institute of Technology may refer to one of two institutes of higher education in Switzerland:
The Fiq is "not just a boring old block of sediment deposited during one profound glaciation," says Allen. On the contrary, Allen and his collaborators report in the October Geology, sediments indicate that glaciers moved back and forth at least seven times during the Fiq's formation. If so, Earth had an active water cycle, which may undermine the snowball theory. "We do not have a single longtime freeze-up in which the water cycle is shut down completely," asserts Allen. "That's not an accurate characterization of the snowball," contends Paul F. Hoffman Paul F. Hoffman is a Canadian geologist and the Sturgis Hooper Professor of Geology at Harvard University. He specializes in the Precambrian era and is widely known for his theory of the Snowball Earth about phenomena that occurred in the Neoproterozoic era, co-published with , the geologist 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. who first described snowball Earth The Snowball Earth hypothesis as it currently stands[2] proposes that the Earth was entirely covered by ice in part of the Cryogenian period of the Proterozoic eon, and perhaps at other times in the history of Earth. . In his current view, the water cycle in low-latitude regions such as Oman would have slowed down, but not completely halted, in the frozen periods. So, formations like the Fiq could have experienced active glaciation, especially as Earth began to warm at the end of each snowball stage (SN: 5/27/00, p. 343). The snowball theorists are backing down on their earlier view that the water cycle shut down completely in the Neoproterozoic period, Allen argues. In the end, he says, "there's either going to be a complete meltdown meltdown Occurrence in which a huge amount of thermal energy and radiation is released as a result of an uncontrolled chain reaction in a nuclear power reactor. The chain reaction that occurs in the reactor's core must be carefully regulated by control rods, which absorb of the [snowball] theory, or it is going to have to be refined." |
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