Earthworm Excrement Could Help Archaeologists Measure Age-Old Climate Conditions

Yun Huang Yong via Flickr

Scientists in the UK have developed a novel idea for taking the temperature of the earth thousands of years in the past—by using tiny lumps of calcium carbonate found in earthworm poop.

In theory, archaeologists can use these lumps to find out exactly what the temperature was at almost any archeological site, by looking at how much oxygen-18 the granules contain. This would be a huge development for archaeologists, as redOrbit explains:

Climate data using instruments only goes back about 150 years. Prior to that period other methods have to be used. In addition to human records, scientists use such techniques as measuring tree rings and ice cores and analyzing pollen distribution.

Adding earthworm poop to the arsenal has several advantages. Tree ring thickness, for example, can be influenced by other things besides climate, including the clearing of surrounding trees. In addition, many of the other methods may use samples that are thousands of miles from the archaeological site. These chalk deposits are right there in the exact same context as the surrounding dig site. This proximity will provide data on more localized environments and increase the accuracy of the climate data at any given place.

The researchers used a common species of earthworm for their experiments, keeping the worms in soils at precise temperatures for weeks, then measuring the chemical content of the chalk-like granules found in earthworm excrement. Because the lumps are composed of calcium carbonate, they can even be precisely dated using uranium-thorium dating, which can be used to date site that are hundreds of thousands of years old. (Carbon dating, by contrast, can only date items accurately to about 50,000 years.)

And it’s not like these calcium crystals in earthworm excrement are hard to come by. Previous research has shown that earthworms produce as many as 30,000 granules per year. The researchers still need to figure out if their method holds true outside of the lab setting, and also whether it works on other earthworm species. If all goes well, they hope to use their new “paleothermometer” to archaeological sites in Germany, the Netherlands and the UK.

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