About a century ago, A.L. Chizhevsky, great Russian biophysicist, was the first to pay attention to the correlation between people's death-rate and the solar activity cycles.
However, in the course of time, it became clear that some powerful natural factor of terrestrial origin interfered in the process. It turned out that there existed a global filter that distributed the solar ultraviolet's influence heterogeneously on various regions of the Earth. This filter turned out to be the ozone layer of the terrestrial atmosphere, the layer being located in the stratosphere. Absorbing the ultra-violet radiation of the Sun, the ozone layer protects the biosphere from the destructive short-wave part of ultra-violet radiation.
Specialists of the Institute of Atmosphere Optics, Northern Branch, Russian Academy of Sciences, took advantage of the fact that excess ultra-violet radiation caused stress to growing trees, the annual rings becoming more dense than the usual ones as the thickness growth of the trunk slowed down. At the end of the last century, geophysicists learned to measure the ozone content both from the Earth and from outer space. That gave the Tomsk researchers an opportunity to compare the ozone observation data within the last 20 years and the respective density of annual rings within the same period. This effort resulted in a formula, which allowed to calculate the ozone concentration in the atmosphere based on dendrochronological data - through measuring the annual rings kept in the International WSL Bank.
Combining the calculations with the death-rate statistics in a certain region within the period under consideration, the researchers can easily review the role played by ozone in the life of region's population. The method invented by the Tomsk biophysics will come in handy to the researchers dealing with paleo-ecology - i.e. reconstruction of natural conditions of the distant past.
Applying this method, the researchers reconstructed the dynamics of ozone screen above Balaam and, for comparison, above Switzerland since 1700 through 2000. Charts of these changes did not coincide, which is quite natural in the scientists' opinion, as ozonosphere is heterogeneous in the space. Then the researchers reconciled the obtained data with the St. Petersburg death-rate statistics for the 18th - 19th centuries and the solar activity observations. As a result, they have learned that the solar activity did not play a significant role. Instead, the link between the death-rate and ozone concentration curves was evident: the lower the ozone concentration was, the more deaths hit that period. The specialists believe that if the solar situation is more or less calm, people are more dependent on the ozone protective action than on minor whims of the Sun.