The cycle is based on the 12,800 years between transits of our galactic plane. We pass thru the galactic plane... the densest part of our galaxy, the mid-line of the 'saucer'... every ~12,800 years... more bodies, comets, gravity, etc. This, in turn, causes a much higher probability of impacts, gravitational effects (translating to seismic/volcanic activity), etc. The ~6000 year period is us 'changing direction' within the galactic electric sheet... i.e. reaching the extreme ends of the 'sine wave' of our orbit above/below the galactic plane.
The cycle is based on the 12,800 years between transits of our galactic plane. We pass thru the galactic plane... the densest part of our galaxy, the mid-line of the 'saucer'... every ~12,800 years... more bodies, comets, gravity, etc. This, in turn, causes a much higher probability of impacts, gravitational effects (translating to seismic/volcanic activity), etc. The ~6000 year period is us 'changing direction' within the galactic electric sheet... i.e. reaching the extreme ends of the 'sine wave' of our orbit above/below the galactic plane.