In the summer of 1964, graduate student Donald R. Currey cut down a bristlecone pine in what is now Great Basin National Park, Nevada. The tree was known to local climbers as Prometheus. Only after it was on the ground did he realize he had felled what was then the oldest tree ever dated.
Bristlecone pines are among the hardiest trees. They grow slowly. Their dense wood resists weather, insects and fungi, and they often look twisted. One kind, the Great Basin bristlecone pine, can live for thousands of years.
Currey had not heard of them before graduate school. Then his mother sent him a magazine article by Edmund Schulman, the researcher who had sampled another famous bristlecone pine, Methuselah. Currey was a geographer. He thought the trees might help him date glacial features below Wheeler Peak, where he was doing fieldwork.
A tree's growth rings record the climate in the years they formed, which can also hint at what glaciers were doing. In ancient bristlecone pines, that record can run for thousands of years. To read it, researchers usually use a borer to take a pencil-sized cylinder of wood, called a core sample.
The US Forest Service gave Currey permission to core a group of bristlecone pines beneath Wheeler Peak, including Prometheus. On that tree, the usual method failed. "The normal approach to coring the tree wasn't working because the largest available increment bores were too small to core even from several angles," Currey said in a 2001 documentary. With further permission from the Forest Service, Prometheus was cut down, and a 30-centimeter (1-foot) cross-section was taken from the trunk.
Currey had already suspected the tree was over 4,000 years old. Only when he counted the rings did he see what he had done. "We could begin to see that we were getting over 4,000 years, over 4,500, over 4,600, which was the oldest record that had been reported in the literature up until that time," he said. "And we ended around 4,900 years. And you've got to think, 'I've got to have done something wrong. I better recount.'"
There was no mistake. Prometheus was about 4,900 years old, then the oldest tree ever dated, and it was dead. No one knew how significant it was before it was cut.
Today its stump still sits among similarly colored rocks. A slab of the tree is on display at the Great Basin Visitor Center, where visitors can count the rings themselves.