[Quasi-eleven year modulation of global and spectral features of geomagnetic disturbances].

Variations in spectral characteristics of the Kp-index of geomagnetic activity during the solar activity cycle were studied in order to assess the role of its rhythms in the formation of temporal structure of biological objects. It is shown that most spectral components of the Kp-index are modulated by the 10.5-year periodic rhythms in solar activity variations, while its circasemiseptan component (3.5 days) exhibits an 11-year rhythm. Since it is a circasemiseptan rhythm that is characteristics of biological objects (e.g., unicellular algae), it can be assumed that geophysical rhythms played a substantial role in the formation of biological rhythms during evolution.