That’s great, it starts with an earthquake, every 26.2Myrs.

It’s not often that reading a research paper makes me literally jump up in my seat and yell “Holy shit!,” but that’s what I did when I saw figure 1.

A fascinating new paper is up on the arXiv today about the Nemesis Hypothesis. This hypothesis originated in the 1980’s, when people noticed that mass extinctions tended to happen every 27 million years or so, and it was suggested that this may be because some hard-to-see star — perhaps a red dwarf — is orbiting with our sun in a very eccentric orbit, passing close to us only every so often and in the process pulling in hordes of comets from the Oort cloud and bringing about death and destruction. (A second periodicity, of roughly 62M years, also exists; it’s known that these extinctions also seem to be tied to oscillations in the sea level, so comets are considered a less likely source and there’s no analogous Nemesis2 hypothesis that I know of)

What the new paper did was accumulate a very detailed record of extinction rates over the past 500Myrs, using all of the best datasets available, and produce a plot of the fraction of species going extinct per unit time. The Fourier transform of this curve is simply shocking: it shows two extremely clear peaks at periods of 62 and 26.2Myr, respectively. Amazingly, these peaks are clear enough to rule out the Nemesis hypothesis; if the periodicity were due to a star’s motion, it would actually have to be less perfectly regular  than the experimental data, because the star’s motion would be perturbed by other stars, the galactic disk, and so on. (Good summary paper of that)

I was up much later than I should have been reading through these papers and thinking through the results. Some things seem clear:

  1. These guys seem to have done fairly serious numeric analysis. I’m not qualified to evaluate their data sources and prospective issues from that side, so I’ll have to wait for the specialist community to weigh in, but I didn’t see any red flags in the paper. From looking at the Nemesis papers, it seems pretty clear that if their statistical analysis is good, then Nemesis is genuinely ruled out; I couldn’t think of any variations on that hypothesis which would survive this data.
  2. The peaks on the graph in this paper are holy-shit sharp and distinct. Something is happening with clockwork regularity that wipes out most of life on Earth.

I’m now spending some time thinking about this and about what these spikes may mean. One interesting question is whether the 62My and 26.2My peaks are related or if they’re caused by completely disjoint phenomena. Interestingly, there’s another bump on the graph at about 17My, although it looks like it’s just above the level of statistical significance, not quite big enough to tell for sure if it’s a real signal. If there is a bump there, then these bumps have the odd property of being evenly spaced in frequency space, at intervals of about 0.02 My-1. The pattern of frequencies ω0+nω1 is familiar from many differential equations — e.g., it’s the pattern of energy levels of a quantum-mechanical harmonic oscillator — so it’s something which could naturally emerge from a fairly wide range of physical phenomena.

On the other hand, the two could be wholly separate, or they could be the only two real spikes. It’s going to be hard to tell without staring some at the raw data, and even then we may not have enough precision to really know. One thing which I do suspect we’ll be able to determine from this dataset is whether either of the two cycles could be coming from purely biological or other complex systems such as Clathrate guns — such systems seem less likely to have extremely precise and stable periods. Honestly, the first thing that pops into my mind when I see this level of stability is pulsars or astrophysical jets; we don’t know a lot about super-long-period pulsars, but because they have such long periods it would be awfully hard to know a lot about them by nature. Call this the “Cosmic Death Ray Hypothesis.” Other interesting possibilities could be long-frequency oscillations of the Sun, or something resonating in the structure of the Earth… although the latter seems a bit less precise to me.

Definitely time to look at the raw data. A lot of this hypothesizing depends on just how tight the error bounds on this data really are. If they’re as tight as they seem from the graphs, this is an amazing source of data.

The good news: We’re still about 16My from the next predicted peak in this cycle, so we’ve got a little while to figure it out. Before the cosmic death rays come to get us.

ETA: There’s a good post about this on the arXiv blog which gives some more context.

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Published in: on July 12, 2010 at 11:16  Comments (4)  
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4 Comments

  1. Fascinating.

    One commenter on the arXiv article points to another paper that seems to reject any real periodicity in extinctions. The commenter claims that this other paper makes use of better raw data and better numerical analysis. I’m completely unqualified to judge either of these claims, but the commenter does at least seem to have done some homework. Any chance he has a point?

    • It’s quite possible. I’d really like to understand the data sources better; I don’t feel that I have a good sense for what the error bars are in this plot, both from statistical and systematic sources.

  2. What is interesting to me is that… if it is true… couldn’t we get a good understanding of what it might be by analyzing what life forms survived each time it happens? That might make it a lot easier to hypothesis
    the cause.

    • That’s an interesting idea. I think that the biggest risk is that it would produce too blurry a signal, something on the lines of “everything which had a robust ecological dependency tree survived; everything which didn’t, died.” For example, any catastrophe which knocks out a base element of a major food chain is going to kill anything else in that chain which can’t find substitutes really quickly.

      On the other hand, that’s far from guaranteed. I think you’re right that the details of these extinctions will have some useful data for tracking this down…


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