New research shows that ancient animals survived about 8,000 years later than previously thought

Frozen soil samples collected about ten years ago are rewriting our understanding of iconic animals of the Ice Age, such as mammoths. Soil samples were taken from Canadian permafrost in the early 2010s, but work on them has not been published until recently. According to a study published this week in the journal Nature Communications, a new analysis of DNA samples shows that mammoths, wild horses, and prairie bison appeared about 5,000 years ago — about 8,000 years later than previously thought .

According to Isaac Schultz of Gizmodo, most DNA samples are taken from materials such as bones or hair, but soil also contains genetic residues left by animals when they move in the environment. The soil samples were kept in untested refrigerators for many years, until Tyler Murchie, an archaeologist specializing in ancient DNA at McMaster University, decided to investigate them again.

“I found them in the refrigerator when I was looking for new items during my Ph.D.,” Murchie, the first author of the new paper, told Gizmodo. "One of my duties at the ancient DNA center is to maintain the refrigerator, so I know very well that there might be something cool waiting for someone to study it."

The research team is eager to understand how and why large North American species such as mammoths and bison survived thousands of years before disappearing. During the Pleistocene-Holocene transition about 11,000 to 14,000 years ago, the climate experienced rapid changes, leading to the extinction of many ice age species such as mastodons and saber-toothed tigers. Based on previous research, scientists suspect that there are two factors that contributed to the extinction: a warming climate that leads to food loss or human over-hunting. Murchie told Gizmodo that this is a problem that scientists have been trying to solve for about 270 years. In the new paper, Murchie's team provides a DNA record of plant and animal communities dating back 30,000 years. 

“Just by collecting tiny spots of dirt — in this case, about 0.5 to 1 gram, which is very little sediment — we can rebuild the entire ecosystem with the various animals that exist in the area,” Murch Talk to Sebastian Lake of CBC.

Scientists used radiocarbon dating of plant materials in the soil combined with microscopic genome sequences from animal species to reconstruct ancient ecosystems. Their results were unexpected: before the climate warmed, large mammals such as mammoths and horses were already declining. Murchie and his colleagues recently discovered evidence of DNA from mammoths and North American horses 5,000 years ago, which means that these animals survived until the mid Holocene.

"Now that we have these technologies, we are aware of how much life history information is stored in permafrost," Murch said in a statement.

Scientists like Murchie have limited time to sample DNA captured from permafrost, because human-induced climate change is melting the permafrost. As the permafrost melts, the DNA trapped in the frozen soil decomposes and the stored carbon is released into the atmosphere, which further warms the earth.

Corryn Wetzel is a freelance science journalist based in Brooklyn. Her work has also appeared in Audubon Magazine, National Geographic and other magazines.

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