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The world’s largest tree has been rigorously dated for the first time, confirming it is at least 16,000 years old.

Named Pando, the tree is a quaking aspen (Populus tremuloides) with around 47,000 stems connected by a root system that sprawls about 43 hectares in Utah’s Fishlake National Forest. It has long been thought to be among the most ancient living things on Earth, but scientists didn’t know for certain how old it is.

at the Georgia Institute of Technology, Atlanta, and her colleagues collected leaves, roots and bark samples and then extracted genetic data, looking in particular for somatic mutations, which are changes in DNA that occur in an organism’s cells after conception.

“At first, when Pando germinated from a seed, its cells all contained essentially identical DNA,” says Pineau. “But every time a new cell is made and the genetic information is replicated, mistakes can occur, introducing mutations into the DNA.”

By looking at which mutations are present in different parts of the tree, the researchers could reconstruct Pando’s life history and estimate its age.

Assuming that they correctly identified every mutation in the part of the genome they sequenced, their results suggest Pando is about 34,000 years old.

But Pineau and her team were unsure whether they missed some mutations, or if some of the mutations they identified were false positives. Taking these uncertainties into account, they calculate that Pando’s age is likely to be between 16,000 and 81,000 years.

“While these scenarios give us quite different numbers, they all point to one remarkable conclusion: Pando is ancient,” says Pineau. “Even at its youngest estimated age, this aspen clone has been growing since the last ice age.

“This finding aligns beautifully with other evidence, such as pollen samples from a nearby lake that show aspens have been growing continuously in this area for at least 15,000 years, and been fairly well represented for the last 60,000 years.”

Pando might even be the oldest living organism on Earth. The other contenders include another clonal tree from Tasmania, Lomatia tasmanica, estimated to be , and a patch of Posidonia oceanica seagrass in the Mediterranean, which may be up to 200,000 years old.