  Recent experiments elucidated the structure and function of the
cyanobacterial circadian oscillator, which is driven by sunlight intensity
variation and therefore by Earth's rotation. It is known that cyanobacteria
appeared about 3.5 billion years ago and that Earth's rotational speed is
continuously decreasing because of tidal friction. What is the effect of the
continuous slowdown of Earth's rotation on the operation of the cyanobacterial
oscillator? To answer this question we derived the oscillator's equation of
motion directly from experimental data, coupled it with Earth's rotation and
computed its natural periods and its resonance curve. The results show that
there are two resonance peaks of the "cyanobacterial oscillator-rotating Earth"
system, indicating that cyanobacteria used more efficiently the solar energy
during the geological period in which the day length varied from about 11 to 15
hours and make more efficient use of solar energy at the geological period
which started with a day length of 21 hours and will end at a day length of 28
hours.
