By Sid Perkins
From Calgary, Alberta, at the Earth Systems Processes 2 meeting of the Geological Society of America and the Geological Association of Canada
The chemistry of plant spores on a frigid Antarctic island chronicles decreasing concentrations of ozone over the region in recent decades. Scientists may take advantage of that trend to learn about ancient extinctions.
At far-southern latitudes, the concentration of stratospheric ozone—an atmospheric constituent that provides protection against the sun’s ultraviolet radiation—has dropped about 14 percent in the past 4 decades, says Barry Lomax of the University of Sheffield in England. Over that same period, the concentration of an ultraviolet-absorbing pigment in the spores of a particular club moss has more than tripled. Lomax and his collaborators studied spores from South Georgia Island, a tiny landmass near Antarctica.
The protective pigment, called sporopollenin, and several of its long-lived breakdown products absorb a specific wavelength of ultraviolet radiation, says Lomax. That makes these substances easy for researchers to measure.
Analyses of the compounds in ancient spores of various ages could identify long-term fluctuations in atmospheric ozone. Such changes could have been caused by major volcanic eruptions, the impact of large extraterrestrial objects, or upheavals in atmospheric chemistry—all of which scientists suspect may be associated with some of Earth’s previous mass extinctions.
