Putting known concepts together..

I know that changing levels of UV exposure would result in changes in melanin levels. I also know that heavy exposure to UV can cause massive extinction. But I couldn't put the 2 together… It's not even rocket science. -.-

 

Spores may fill gap in atmospheric records.

A gaping hole in atmospheric scientists' records could soon be filled thanks to the spores of a primitive moss.

Led by Barry Lomax, at the University of Nottingham, UK, a team of researchers has devised a way to reconstruct past levels of ozone by measuring levels of the chemicals that act as protective 'sunscreens' in the spores.

Lomax had previously used this technique to try to find out whether massive exposure to UV radiation caused the Permian extinction around 250 million years ago, after volcanic eruptions triggered a massive loss of ozone (see 'Plant pollen records ozone holes'). Although that attempt failed because of a lack of suitable fossils, the technique may end up answering wider questions about the evolution of our atmosphere.

Until now, atmospheric scientists have been limited to ozone measurements made by satellites that date back only to the late 1970s and data from ground-based spectrophotometers going back to the 1920s. Lomax's team say that the levels of ultraviolet-absorbing compounds in plant spores can show how much of this radiation they were exposed to, and hence show what the ozone levels were in the atmosphere millennia ago.

"At the moment it's very much an unknown how ozone has changed over recent and geological time," says Lomax. "[This method] could help address issues of climate change and whether we're seeing recovery [in the ozone layer] now, or whether it's natural variation."

The story's in the spores

In a paper published online by Nature Geoscience Lomax details how spores can be use as a 'biological proxy' for ozone levels. Plants subjected to increased levels of UV-B radiation make more of the natural phenolic 'sunscreen' compounds that absorb the potentially harmful rays¹.

By analysing the concentration of these UV-absorbing compounds in the walls of spores from herbarium collections, it is possible to work out how much radiation they have been subjected to. From this it is possible to work out how much ozone was in the atmosphere between the plant and the Sun, says Lomax.

Traces of these compounds are even preserved in fossils. "We certainly should be able to go back into the Tertiary, about 55 million years ago, without a problem," says Lomax. "It will work on fossil spores provided they haven't been heated to over 200 ºC."

The paper details analysis of spores of clubmosses from high- and low-latitude locations, which were found to contain concentrations of UV-absorbing compounds that strongly correlate with known historical changes in UV-B levels. Spores from Ecuador, where there have been no historic changes in UV-B, showed no change in 'sunscreen' concentrations over the same time period.

Using spores from Greenland, Lomax reconstructed historical ozone levels between 1907 and 1993 and found strong correlations between their reconstructions and atmospheric ozone measurements made within this period.

"It would be extremely interesting if we could reconstruct the UV climates in the past," says Geir Braathen, an atmospheric chemist and senior scientific officer at the World Meteorological Organization in Geneva, Switzerland. "It would be very interesting to see how the ozone layer has developed."

Lomax now hopes to do just that. "We're planning to look through to the Holocene and the Quaternary to see just how far back we can take it," he says.

• References
  
  • Lomax, B. et al. Nature Geosci. advance online publiction doi:10.1038/ngeo278 (2008)
    

http://www.nature.com/news/2008/080831/full/news.2008.1071.html?s=news_rss