Earthworms left behind calcite crystals (essentially their feces) and they may be the most precise way to measure climate conditions during the last Ice Age in northern Europe.
In a new study, researchers turned to these crystals — which were ever-present in the top layers of soil and just a few inches below the permafrost for tens of thousands of years — as the basis of radiocarbon dating and uncovered new information about the climate in ancient times.
Why it matters: Scientists continue to argue about why and how Neanderthals died out in northern Europe some 40,000 years ago as modern humans moved into their territory. Climate conditions almost certainly played in the transition, but anthropologists and paleo-climatologists have struggled to define the climate during and immediately after the Ice Age began to retreat because there is a scarcity of organic remains like wood, charcoal and bone to test.
What they found: With the help of more precise dating from the earthworm crystals, researchers found that there was greater climate variability between the mid- and high-latitude regions of Northern Europe between 47,000 and 20,000 years ago; that permafrost was more permeable at certain times and some regions were more arid than had previously been understood. The researchers found radiocarbon dating using earthworm crystals had a substantially lower margin of error (as much as two-thirds) compared to other methods using sparse organic material.
How it works: The ratio of different forms of oxygen in the calcite crystals depends on the temperature as the worm moves through the soil. By analyzing those proportions, the researchers get a measure of the climate at the time.
Fun fact: Charles Darwin was the first to discover that earthworms leave behind calcite crystals as they make their way through the soil. He was fascinated with worms and now, nearly 150 years later, his finding may help us understand what happened to the Neanderthals.