Earthworms could help reveal what the prevailing weather conditions were thousands of years ago, according to a team of UK researchers.
A laboratory study by researchers from the Universities of Reading and York has demonstrated that balls of calcium carbonate (small lumps of chalk-like material) excreted by the earthworm Lumbricus terrestris - commonly known as lobworms or nightcrawlers - maintain a memory of the temperature at which they were formed.
This, say the researchers means that calcite granules, commonly recorded at sites of archaeological interest, have the potential to reveal important information about past climates which could be used to enhance and benchmark climate change models.
The study, which also involved English Heritage's Centre for Archaeology, was funded by the Natural Environment Research Council (NERC). Lead author Dr Emma Versteegh from the Department of Geography and Environmental Science at the University of Reading, said: "These chalk balls will allow us to reconstruct temperatures for specific time intervals in which they were formed. Reconstructions like this are interesting for archaeologists, because they give a climatic context to their finds. More importantly, climate proxies are the only means we have to study climate beyond the instrumental record, which only goes back about 150 years."
"This knowledge about past climates is of vital importance for developing and benchmarking climate models that make predictions for the future. Many different proxies already exist, but no proxy is perfect, or is available in every location, so it is good to have many different ones."
The proof of concept study involved keeping modern-day Lumbricus terrestris at different temperatures, then carrying out isotopic testing on the calcite granules excreted. This successfully demonstrated that the granules remembered the temperature at which they were formed.
Principal Investigator Professor Mark Hodson from the University of York's Environment Department, and formerly of the University of Reading, said: "There are many conflicting theories about why earthworms produce calcite granules, but until now, the small lumps of chalk-like material found in earthworm poo have been seen as little more than a biological curiosity. However, our research shows they may well have an important role to play, offering a window into past climates."
The study has been published in the journal Geochimica et Cosmochimica Acta.