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Lupine seeds once thought to be 10,000 years old, but now known to date from the 1950s
The oldest viable seeds in the world, dating from the Pleistocene era, are not what we thought.
New dating techniques have revealed that the seeds, which have been grown into live Arctic lupine plants, are not 10,000 years old as believed.
Instead they are modern seeds which contaminated ancient rodent burrows.
However, it remains possible that plants may yet be grown from seeds trapped in ice age permafrost, says the scientist who debunked the record.
More than four decades ago, Canadian scientists published details in one of the world's foremost scientific journals of how they discovered two dozen seeds of an Arctic lupine plant within ancient lemming burrows.
In Science, they described how these burrows, found at Miller Creek within the Yukon territory of western Canada, had been buried deep within frozen silt since the Pleistocene.
That made them over 10,000 years old. As well as rodent nests, faecal pellets and seeds, they also contained an ancient lemming skull, further confirming their old age.
Crucially, the seeds remained viable, as the scientists managed to germinate and cultivate normal healthy Arctic lupine (Lupinus arcticus) plants from them.
"These were considered to be the oldest viable seeds to have ever grown," says Grant Zazula, a scientist working for the Yukon Palaeontology Program run by the Government of Yukon, based in Whitehorse, Canada.
But the idea that seeds could remain viable for so long immediately attracted controversy.
"The scientific community was really split by that presumed ancient viable Arctic lupine seeds. Some believed it, others did not," says Zazula.
The controversy rested on the methods used at the time to date the seeds.
When the researchers published the original claim in 1967, there was no way of radiocarbon dating small samples the size of seeds.
Pleistocene lemming skulls found alongside the seeds
Instead, the seeds were presumed to be of the same age as the ancient frozen lemming burrows in which they were found.
But through his own research into ice age fossils, Zazula became suspicious of the seeds' provenance.
Studying ancient rodent nests buried in the Yukon permafrost, some up to 25,000 years old, from which he had recovered seeds from around 65 different plant species, Zazula had never found any 'ancient' Arctic lupine seeds.
"Also, Arctic lupine is a boreal forest understory flower, and I do not think it lived during the ice age with incredibly cold, harsh arctic conditions. The ecology does not fit," he says.
So Zazula contacted Richard Harington of the Canadian Museum of Nature, one of the authors of the original 1967 Science paper about the seeds.
Harington told Zazula that some of the seeds still existed, though they were coated in paraffin wax to preserve them.
Zazula recruited Fiona Brock, an expert in radiocarbon dating from the University of Oxford, UK and together the researchers found a way to avoid the contamination from the paraffin, and accurately radiocarbon date the seeds for the first time.
The Pleisotocene seeds, it turns out, appear to be from between 1955 and 1957, Zazula's team report in the journal New Phytologist.
A modern Arctic lupine in bloom
The radiocarbon dating did confirm that the lemming skull found alongside the seeds was from the Pleistocene. That validated the original researchers' claim that they had collected Pleistocene samples from deep within the permafrost.
But without their knowledge, the seeds must have fallen into the burrows just years before they were collected. The burrows had likely been exposed by mining activity in the region.
"I was excited that we were able to put a controversy to rest," says Zazula.
"The 'ancient' viable Arctic lupine seed is cited throughout seed germination text books, studies on permafrost and throughout the botanical literature. So, it was nice to be able to conclusively demonstrate the actual age of the seeds."
"The take home message is that any claims for ancient seed viability must be accompanied by rigorous dating methods. If you are going to say something is really old, the research has to effectively demonstrate their age."
Ice age plants
However, Zazula suspects that ancient seeds will yet be discovered that remain viable, and that live plants could still be grown from them.
"The record now for the oldest viable seeds is held by a 2,000-year-old date palm recovered near the Dead Sea," he says.
In 2002, Russian scientists published a claim that they had germinated a 33,000-year-old seed of a small tundra flower (Silene stenophylla).
But they published their work in a relatively unknown journal, and the claim has received almost no acceptance in the scientific community, Zazula says.
Yet "although we have shown that these Arctic lupines were not old as previously thought, I still think that in the near future we will be able to grow ancient, ice age seeds that are preserved in permafrost," Zazula says.
Indeed, studies are already underway to attempt to germinate real ancient seeds from the Yukon permafrost, he says.