In today’s Academic Minute, Dr. Emma Versteegh of the University of Reading explains how earthworms create a chalky record of the climate.
Emma Versteegh was a postdoctoral researcher in the Department of Geography and Environmental Science at the University of Reading. She recently assumed a postdoctoral post at the California Institute of Technology. She earned her Ph.D. at the University of Amsterdam.
Dr. Emma Versteegh – Earthworms and Climate History
In 1881 Charles Darwin published his last book, which was dedicated to earthworms. He noted that some earthworms produced calcium carbonate granules - balls of chalk up to 2 mm in size. Ever since then, the earthworm granules have been a mystery as to their function and how they are produced. However, these granules are regularly encountered in archaeological finds and buried soils and so are potentially useful archives of past environmental conditions.
Other calcium carbonates, like sea shells, corals and stalagmites, are known to be useful as climate records as they record either temperature, composition of rainfall or sometimes both.
The aim of our research was to find out what the earthworm granules recorded, for how long and if we could work out how this was controlled. We focussed on the species Lumbricus terrestris, also known as the lobworm, since it is one of the major producers of calcium carbonate in its native Europe, and as an invasive species in North America. We analysed the oxygen isotope composition of calcium carbonate granules produced by worms that were kept in soil for a month at a range of temperatures. Our findings show that earthworm granules faithfully record temperatures in a similar way as many aquatic animals. This means that by analysing granules from archaeological finds or buried soils, we can directly determine the full seasonal range of temperatures at the time they were formed.
Reconstructions like this are interesting for archaeologists, because they give a climatic context to their finds. As the chalk balls are found in direct context with archaeological finds, they will reveal temperatures at the same location. In addition, we can directly date the granules so we can have an independent climate record associated with the archaeological materials.