Determining absolute ages by radiometric dating

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The longest cores have helped to form a record of polar climate stretching hundreds of thousands of years back.

These thick layers alternate with thin, clay-rich layers deposited during the winter.Not surprisingly, these methods resulted in wildly different estimates, from a few million years to "quadrillions of years".Probably the most reliable of these estimates was produced by the British geologist Charles Lyell, who estimated that 240 million years have passed since the appearance of the first animals with shells.To study these patterns, scientists drill deep into ice sheets, producing cores hundreds of meters long.Scientists analyze these ice cores to determine how the climate has changed over time, as well as to measure concentrations of atmospheric gases.

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