Scientists announced a new discovery about earthworms this week, saying the tiny calcite granules found in their excrement actually contain a detailed record of Earth's climate history.
In a study published Monday in the journal Geochimica et Cosmchimica Acta, researchers from the University of Reading and the University of York explained that the chalky lumps of calcium carbonate appear to be uniquely marked by whatever temperatures they encountered in the surrounding environment at the time the worm pooped them out.
"There are many conflicting theories about why earthworms produce calcite granules, but until now, the small lumps of chalk-like material found in earthworm poop have been seen as little more than a biological curiosity," University of York's Professor Mark Hodson said in an advisory. "However, our research shows they may well have an important role to play, offering a window into past climates."
This window into past climates is especially helpful to scientists who study climatic patterns, particularly as they relate to global warming. There is no longer a debate in the scientific community as to whether the planet's annual average temperature is warming due to human activity, but because man-made recordings of the temperature only go back about 150 years there remains some discussion as to whether this warming is without precedent.
Today, scientists rely heavily upon the climate records stored deep within polar ice, drilling out core samples from deep ice to find ancient, untouched stores of trapped atmospheric gasses. That's how scientists know that the Antarctic's summer ice is thawing this year at a rate that's 10 times faster than at any point in history, among other discoveries this innovation has led to.
Tree rings have also been used by scientists to help track climate changes from year to year. The U.S. government's National Climatic Data Center even runs a program called the International Tree-Ring Data Bank. "In mid- to upper latitudes, or areas where there is seasonality in temperature and/or precipitation, many species of trees form annual growth rings," the Laboratory of Tree-Ring Research at the University of Arizona explains. "Because the same set of environmental factors influence tree growth throughout a region, the patterns of ring characteristics, such as ring widths, are often common from tree to tree."
This latest discovery in earthworm poop, of all places, is likely to bring Earth's past climate into even sharper focus than the portrait painted by ice cores and tree rings. Scientists said that's due to the geographic specificity of the calcite granules being able to record the climate at the time and place they were created. Added, it's simply a fact that earthworms poop all year long, so there's plenty of these little climate records lurking in the soil below.
"We believe this new method of delving into past climates has distinct advantages over other biological proxies," University of Reading Professor Stuart Black said in an advisory. "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."
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