Biodiversity fashionable every 62 million years
- Biodiversity fashionable every 62 million years ››
- Rohde and Muller find biodiversity, as measured by marine animal fossil genera through the Phanerozoic, fits rather well to a beautiful sine wave with a period of 62±3 million years. I'm not qualified to comment on their maths but the cycle is pretty obvious even in the raw data. The implications are astonishing: one author posits an astrophysical cause and the other a geophysical cause but, as pointed out elsewhere, these are catastrophes and therefore unsatisfactory explanations for the multimegayear pace of sining biodiversity. What could cause the number of genera (not number of species, which might reflect environment and niche availability, nor number of individuals, as significantly amended during extinction events) to wax and wane like that? The authors show it isn't an artefact of the data with an obvious cause, and, assuming its reality, they cross off a number of realistic astro- and geophysical explanations: molecular clouds and their effects on cometary impact rate; periodic volcanism due to mantle plume cycles; the oscillating path of the solar system across the galactic plane; long-period fluctuations in solar weather; terrestrial orbital oscillations with gross climatory effects; nemesis or something like it; and planet X. Other explanations they don't consider: perhaps it takes 62 Mya for an intelligent species to arise and annihilate itself; perhaps there's an uber-cycle of bad gamma ray weather; perhaps unfriendly aliens on a tour of duty get round to us every quarter spin of the galaxy. (via)
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