Release Date 09 July 2013

Earthworms could provide a window into past climates, allowing scientists to piece together the prevailing weather conditions thousands of years ago.

A 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.

Knowledge of past climates is of vital importance for developing and benchmarking models that make predictions for future climates. Many different proxies already exist but no proxy is perfect, or is available in every location, so it is imperative to have many options.

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.

The study, which also involved English Heritage's Centre for Archaeology, was funded by the Natural Environment Research Council (NERC) and published in the journal Geochimica et Cosmochimica Acta. The researchers kept modern-day Lumbricus terrestris at different temperatures, then carryied 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 researchers are now gathering samples from archaeological sites dating back thousands of years in preparation for isotopic testing.

Dr Stuart Black, from the University of Reading's Department of Archaeology, added: "We believe this new method of delving into past climates has distinct advantages over other biological proxies. For example, we believe it will work for the full seasonal range of temperatures whereas methods such as tree rings, do not ‘record' during winter. In addition, because the chalk balls are found in direct context with archaeological finds, they will reveal temperatures at the same location. At present, links are often attempted with climate proxies many hundreds or even thousands of miles away."

ENDS