The interesting question is, have mass extinction events been periodic?
“The interesting question is, have mass extinction events been periodic?”
I think a 400 million year cycle has been identified.
The solar system oscillates “up” and “down” through the galactic plane on an approximately 400 MY cycle. Thus, every 400 MY the earth passes through a denser segment of the galactic arm in which it lies.
Theories say that this increased density may spawn an increase in extraterrestrial comet and asteroid activity in the solar system.
Theories.