Its not very relavent to this. The apparent periodicity of extinctions in the fossil record, if real, has been attributed to many things, one of the more plausible being tidal disruption of the oort cloud as the solarsystem passes through the galactic plane of our galaxy. This diruption then sends a swarm of comets to the inner solar system, increasing the chances of impact with earth.

The excess radiocarbon is generated by high energy cosmic rays, either through close supernovae, or through large solar flares. There have been a few models suggested to explain this radiocarbon excess, other than supernovae and flares, such as a galactic gamma ray burst, a comet impact with the sun, and a comet impact with earth, but the most convincing so far is the large solar flare/solar proton event. The comet impact with earth though has been shown to be higly implausible, since in order to acount for the amount of excess radiocarbon, the comet would be so large extinction events would have occured.

Jinny

The path to good scholarship is paved with imagined patterns. - David M Raup