Chronometry of pedogenic and stratigraphic events from calcite produced by earthworms

• Biomineralised calcite from earthworms can be radiocarbon dated.
• We located sealed sites of known age where earthworm granule dating could be tested.
• The dates derived from earthworm calcite are the true date of granule formation.
• The distribution of dates gives evidence for pedogenic processes, site formation and dissolution.

Dating phases of pedogenesis, soil carbonate deposition or even the burial of whole soil profiles using 14C is a valuable goal in archaeology and pedology, but one that has been consistently hampered by the presence of old carbon skewing the measurements to produce apparent dates older than the true formation date. Calcite produced by earthworms could be a useful alternative source of datable carbon. Since earthworms both inhabit and ingest soils with an old carbon content, however, the granules could yield a 14C date older than the date of their formation. In this study, by examining granules from two sites of known-age stratigraphy, we show that the radiocarbon date derived from the granules' calcite closely reflects their true formation date, opening up the possibility of using the granules either individually or as distributions of dates to understand soil processes and date sealed archaeological layers.