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
By 71 thousand years ago, the forest had become savannah. Perhaps this was caused by the sudden drop in world temperatures after the Toba supervolcano 74,000 years ago. Colder weather is drier weather. Incidentally, a bad hurricane season is predicted this year as El Nino is over and Atlantic ocean temperatures are already unusually high.