Nature Geosci. doi:10.1038/ngeo278 (2008)

Spores in herbaria around the world may help to push back the record of atmospheric ozone concentrations, according to Barry Lomax, now at the University of Nottingham, UK, and his co-workers.

They think that the quantities of two ultraviolet-B-absorbing compounds (p-coumaric and ferulic acid) present in the outer walls of spores and pollen can serve as a proxy for stratospheric ozone. This is because the less ozone there is in the atmosphere, the more UV-B radiation reaches Earth, and the more UV-B-protecting chemicals plants make.

Lomax's team tested the idea on two species of clubmoss: Lycopodium magellanicum and L. annotinum, from which they reconstructed UV-B flux back to 1907 — 20 years earlier than any previous record. Spores from Greenland and South Georgia, an island in the South Atlantic, gave the same pattern.