Dating Methods

Scientists test soil around fossils to date them, or figure out how old they are. Many people are familiar with carbon dating, or testing how much of a type of carbon, carbon-14, is still in the soil to know the age of the soil. The less carbon-14 in the soil or bone, the older it is. The first carbon test at the dig site was inconclusive, but a second test dated the soil to 28,000 years old. This date seemed too recent because the mammoth herd was much deeper in the soil to be only 28,000 years old. Scientists also dated pollen samples but that test gave a date of only 18,000 years, which was also too recent.

More tests dated another element, uranium, from the enamel of mammoth teeth discovered at the site. This date made more sense given the depth of the bones in the soil. Scientists then tried a new test called optically stimulated luminescence (OSL). Dr. Steve Foreman, former professor University of Illinois, Chicago and current Baylor University professor, is an expert at this newer method. OSL tests the last time quartz within soil saw sunlight. This test dated sediment samples from around, above, and below the mammoth bones. The test determined the soil, and therefore the bones, had last seen sunlight between 58,000 to 73,000 years ago. Based on both of these tests, scientists believe the mammoth herd died in an event between 65,000 and 72,000 years ago. This is the current date range presented at the site.

Last updated: August 2, 2019

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