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Beware the climate change spin. To all -- please ping me to other topics which are appropriate for the GGG list. |
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Stalagmites reveal past climateThe researchers examined four stalagmites from Crevice Cave, the longest cave known in Missouri, located about 75 miles south of St. Louis. The stalagmites appeared to have been broken by natural forces such as floods or earthquakes and were found about 80 feet below the ground surface, says Dorale. The team determined when the stalagmite layers were deposited, then deduced paleotemperatures and the general types of vegetation growing in the vicinity during that era by examining the carbon and oxygen isotopes within the calcium carbonate. The profile showed that the area had been covered by forest 75,000 years ago, but by 71,000 years ago, it was savannah and by 59,000 years ago, had become a prairie. Between 55,000 and 25,000 years ago, the forest had returned and persisted. Dorale explains that the pattern is consistent with climatological records from the ocean.
by Kristina Bartlett and Devra Wexler
GeoTimes, March 1999
Carbon clock could show the wrong timeA study led by physicist Warren Beck of the University of Arizona discovered an enormous peak in the amount of carbon-14 in the atmosphere between 45 thousand and 11 thousand years ago. Living organisms and some geological features absorb stable carbon-12 and radioactive carbon-14, which are present in the air in a well-known ratio. Scientists use carbon dating to determine when objects ceased to absorb carbon by measuring how much of the carbon-14 - which has a half-life of 5730 years - has decayed. Beck and colleagues tested slices of a half-metre long stalagmite that grew between 45 000 and 11 000 years ago in a cave in the Bahamas. Galactic cosmic rays create most of the carbon-14 in our atmosphere, while solar cosmic rays generate a smaller fraction. The Earth is partially shielded from galactic cosmic rays by its own magnetic field and the solar magnetic field, which fluctuates as the solar cycle proceeds. These effects are predictable and are thought to have changed little in the last million years - which means they cannot explain the glut of carbon-14. The team speculates that a supernova shock wave could have produced a flurry of cosmic rays.
The wrinkle pattern on Helen Thomas’ face could likely reveal much the same thing.
ping
Tree rings have been pretty well debunked as a temperature indicator.