31,800 years ago, a squirrel buried fruits inside a Siberian burrow. Thousands of years later, an Ice Age plant was brought back to life using that ancient tissue

Permafrost can preserve things for far longer than ordinary frozen ground, keeping biological material protected from the decay that normally destroys it. Across parts of the Arctic, permanently frozen soil has held on to remains of plants and animals from periods when the climate and landscape were very different from today. One such discovery in northeastern Siberia eventually gave scientists a rare opportunity to study living plant material separated from the modern world by tens of thousands of years.

The discovery, reported by a team of Russian researchers, showed just how long plant material could remain viable under the right conditions. The study was published in the Proceedings of the National Academy of Sciences (PNAS), and the work was led by researchers including Svetlana Yashina and the late David Gilichinsky.

The discovery came from near the lower Kolyma River in Siberia. The area contains layers of ancient frozen sediment and old burrows made by Arctic ground squirrels. Researchers investigating these burrows found that some had been used as food stores, with seeds and fruits left behind inside them.


One particular stash turned out to be much more unusual than an ordinary Ice Age food cache.

A squirrel's food store survived for thousands of years

The ancient burrow was located about 38 metres below the present surface. It was among dozens of ground squirrel storage chambers discovered in the permanently frozen sediments of the region.

Inside were several immature fruits belonging to Silene stenophylla, a flowering plant that still grows in Siberia. Radiocarbon dating of the seeds found inside the fruits placed them at 31,800 years old, plus or minus 300 years.

The fruits had remained in frozen sediment for all those years. The surrounding conditions were important because the low temperatures greatly slowed microbial activity and other processes that normally break down biological material.

Svetlana Yashina, one of the researchers involved in the work, told Radio Free Europe/Radio Liberty: “It shows that permafrost acts as a natural cryochamber.”

The ancient seeds did not simply grow

Finding plant material that old was remarkable, but the researchers still had to work out whether anything inside it was capable of producing a living plant.

Their first approach was to try growing plants from the ancient seeds. That did not produce mature plants, so the team examined other parts of the immature fruits.

They eventually focused on placental tissue, the part inside the fruit connected with the developing seeds. Using tissue culture and clonal micropropagation, the researchers were able to encourage surviving cells to develop into complete plants.

The process produced 36 plants from three ancient fruits. This was not simply a case of planting an ancient seed in soil and watching it grow. The scientists had recovered living cells from the old fruit tissue and used laboratory techniques to regenerate them.

Plants from the Ice Age began flowering

The regenerated Silene stenophylla plants continued developing and eventually flowered. They also produced seeds, meaning the scientists had managed to obtain plants that could complete their reproductive cycle.

Yashina described the achievement in an AFP report published by ABC Science, saying: “For the first time, we managed to recreate a plant with the help of fruits that are 32,000 years old.”

At the time, the result was notable because it pushed the age of plant material successfully regenerated into flowering plants far beyond the previous benchmark. A date palm had earlier been grown from a seed estimated to be around 2,000 years old.

The ancient and modern plants showed differences

Because Silene stenophylla still grows in Siberia, the researchers could compare the regenerated plants with modern examples of the same species.

They examined 36 regenerated ancient plants alongside 29 modern plants grown from seeds collected in the region. The differences became particularly noticeable when the plants flowered.

The ancient plants had narrower and less deeply divided petals, while the modern plants used for comparison had wider and more deeply divided petals. The ancient plants also showed differences in the types of flowers they produced early in their flowering period.

The researchers did not establish exactly what caused these differences. Genetic changes over thousands of years and the effects of growing conditions were among the factors discussed in the study.

A frozen biological archive

The experiment showed that permafrost can preserve ancient plant material under conditions that allow some cells to remain viable for extraordinary periods. The squirrel's burrow had effectively protected its food store from the normal processes of decay.

The researchers also found that seeds produced by the regenerated plants could germinate successfully. Their offspring went through the complete life cycle and retained the characteristics observed in the regenerated plants.

The discovery has also drawn attention to the wider role of permafrost as a natural store of ancient biological material. Similar old seeds and fruits have been found in animal burrows in parts of Siberia, Alaska and Yukon.