Pu-244 is a relatively long-lived isotope of plutonium, with an 80 million year half life. Once upon a time,someone suggested that the Cretaceous extinction might have been caused by a nearby supernova: if so, we should see some Pu-244 around, or so it was thought.  We don’t.

But that needs to be revised: it now looks as if Pu-244 is _not_ made in a supernova.  Instead, it is probably generated by colliding neutron stars.  So nearby supernova over the past couple hundred million years are not ruled out, although they are a priori unlikely.

The asteroid/comet explanation for the Cretaceous extinction is still good.


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13 Responses to Pu-244

  1. Gord Marsden says:

    I’m more along the nemesis theory , Long time ago supernova in an excentric orbit, drops by every 70 million years and kicks comets out of the Oort cluoud for close encounters of the worst kind

  2. ziel says:

    Nearby colliding neutron stars could solve many of our current problems

  3. ignorant reader says:

    any thoughts on the deccan volcanism hypothesis?

  4. Smithie says:

    If we were to follow the more recent extinctions of megafauna and make our guesses based on that, then I suppose the answer must either be lizardmen, aliens, time-travellers, or some combination thereof, perhaps in the form of a syndicate.

    • ziel says:

      I, for one, would not have been thrilled to be on “let’s clear the cave lions out of this den” duty.

      • Smithie says:

        Wouldn’t have liked to tango with one of the bigger rodents from that era, let alone one of the bigger cats.

        A few nights ago, I was sitting outside, and a porcupine came out of the bushes. Didn’t move at first because I thought it might be a skunk. Then because it was too close, and I thought it might swing its tail at me. It came right up to me and sniffed the end of my shoe. For a brief second, I had the fear it might bite through my toe to get at the salt inside.

        • random observer says:

          I prefer the small creatures we have in central Ottawa- rabbits, groundhogs, raccoons, skunks.

          The rabbits have gotten bold- I’ve had one sit and stare at me instead of running away. The groundhogs still seek cover, but they assess me as a threat first. Not as chicken as they used to be. Skunks still rare. Raccoons just look at me as a potential equal and then carry on with their business without further regard. They also seem to understand how to detect oncoming vehicles. Clever buggers. Could probably tear my face off, but show a civilized disinclination to do so.

  5. Abelard Lindsey says:

    A little off-topic. But if a lot of the heavier elements were not made by supernova but by presumably much less common collisions between neutron stars, does this not have implications for the existence of life through out the universe. Some of the heavier elements are used as catalysts in biology. The assumption being that biology would not exist, ir be a lot more limited without these catalysts. There could be large regions of galaxies completely devoid of life simply because there were no neutron star collisions in those areas.

  6. Evidence for several “recent” (< 10 million years ago), “nearby” (< 100 parsecs) supernovae https://www.nature.com/articles/nature17196

  7. Sunoma69 says:

    Supernova or neutron star collision or yet-to-be-discovered real source of trans-uranics.

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