I saw two independently published papers the other day showing a 27.5M year cycle. One was this paper talking about cycles in volcanic activity, another was talking about mass extinctions. Article here: <a href="https://phys.org/news/2020-12-mass-extinctions-land-dwelling-animals-million-year.html" rel="nofollow">https://phys.org/news/2020-12-mass-extinctions-land-dwelling...</a> . I'm going to hazard a guess that the former is very likely a direct cause of the latter. We suspect this to be true of most of the worst mass extinctions, like the Permian extinction. With the dinosaurs it might have been the Chicxulub asteroid impact, or that might have merely been the finishing blow to a system under severe stress from the Decan Traps flood basalt eruptions in India that had been underway for millions of years by that point. There are plenty of indications that species were declining well before the impact.<p>The solar system takes 230 million years to make one complete orbit around the Milky Way, so I don't think this is likely caused by our passage through the galaxy. It's more likely an internal rhythm in activity deep within the Earth.
Looks like bogus statistics to me. (Caveat: I only read the sciencealert link not the underlying publication). But with a sample of 89 "events" over a purported 10-cycle period we are in the small sample realm where it is easy to get spurious apparent relationships.<p>People love to see patterns, and if you aren't really careful you can "prove" a pattern in essentially random data.
For mass extinctions there is the common explanation that it takes a long time after each extinction before enough diversity is built up again for another major extinction.<p>For example after the current Anthropocene one we likely won't have another one any time soon because there is not enough diversity left for a true mass extinction.<p>That gives a natural effect where mass extinctions are spaced with some minimum interval. They're not independent events.
I like the idea that it is a slow charge buildup from galactic ambient high energy rays.<p>These would cause a very slow charge build up, and the piezo electric effect of the earth would come into play. E.g. a very slow quartz crystal clock cycle.