I am in an all day meeting with bio/geo types, as one does, and as I sit here a random thought struck me, since us astronomers will insist on asteroids as the universal explanation for all things
we have a nice medium sized impact structure in Chesapeake Bay,
the ripples seem to have come as far as Pennsylvania, possibly responsible for the rather bothersome acid rock that almost ruined our most recent local attempts to stimulate through the I-99 construction
anyway, the Chesapeake Bay impact structure is about 35 Myrs old.
In fact, at a glance from an outsider, it seems to coincide within the errors, at least the latest errors I have heard of as a non-expert, with the Eocene/Oligocene boundary...
Now this is a moderately significant geological boundary - transition to a lower CO2 and cooler climates, with glaciation, and another burst of mammalian diversification.
Oh, and there was an extinction event - the Grande Coupure.
There were secular geological changes taking place then, notable opening of southern ocean circulation (and remember I Am Not A Geologist)
but, one can't help but wonder.... was the Chesapeake Bay a tipping point?
Or was it just too wimpy an impact?
Ah - wiki already has it - the end of the eocene is already noted to conincide approximately with the Chesapeake Bay impact and another Siberian impact.
Cool.
I think I better go ask a real expert.
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Reminds me of an essay assigned to us in a writing class. It was pretty funny. The gist of it was you have to think through your stories and plan ahead so it reaches a natural conclusion within the format. The example given was if your writing a 500 word essay you don't build up characters and a story line and then, finding yourself at 490 words, tack on a conclusion like: 'Then a metro bus jumps the curb and kills everyone'.
Relying on 'and then an asteroid hit', which conveniently covers any gaps in an otherwise tenuous time line strikes me as a stopgap flourish that conveniently rounds out the story while explaining very little.
true, but...
the thing is asteroids do hit, randomly,
and the impacts are quite major events of planet changing character for the bigger ones
and we do see the scars...
so they have to explain some of the things...
right?
Try google scholar and an abstract browse.
I really wish other fields would get themselves and ADS and ArXiv
Several of the world experts on the Chesapeake Bay impact, and geological effects of impacts will be at dinner tonight.
I'll just ask them.
We were actually just pondering whether you could see the event in the speciation record.
True, asteroids do strike pretty much at random and one or more asteroids may end up as the most likely and reasonable explanation for certain geographical formations. But sketching in an asteroids too early may close off other explanations of what might be a potentially much more complicated process.
Story lines that depending on easy answers, particularly answers involving relatively rare large-scale events that might destroy much of the record of conditions before the event, deserve a slightly more critical review and require some unequivocal physical evidence to back them.
Until there is strong evidence otherwise look for other, less catastrophic, explanations. Too easy to end up in the abrupt and unsatisfying manner of the Greek plays which relied upon deus ex machina to get the hero out of trouble.
Bunch of dinosaurs at the shore of what would become Chesapeake Bay, glancing nervously at their wristwatches, and muttering: "we're 490 words into a science story. This could be trouble."
Ok, I actually consulted with the people who have the data...
There are multiple time resolved iridium/ash impact layers at the oligocene/eocene boundary, and it has been conjectured for some years that there was a cluster of impacts with some smallish time separation (on geological scale) including the Chesapeake Bay and the Siberian multiple impacts - apparently the Russians have some good data. The error on the dating makes it uncertain if there was a causal relation for impacts causing or triggering the extinction/diversification - both the opening of the south polar waters and antarctic glaciation, and a substantial CO2 draw down happened at similar times, though possibly a little later.
So, looks like we had a medium cometary shower about 35Myrs ago, with enough hits to cause some effects, and possible consequential in the major geological era transition then.
For real.
I'd like to know what the biggest impact is that definitely isn't associated with an extinction event.
"I really wish other fields would get themselves and ADS and ArXiv"
So do we. But how?
The biggest non-extinction event crater... hmm. Depends.
Like on what you define as an "extinction event".
But, it depends, 'cause of contingent things - a smallish asteroid hitting the south polar ice cap does not have the same effect as the same impact north-west of Australia - you hit a biodiversity hotspot even a small impact can cause significant extinction.
The Chesapeake Bay crater is 85 km and sixth biggest known crater... statistically it ought to be in the top 100-200 craters that actually ever existed.
But, if I had to pick a number, then probably somewhere around 30 km you'd start expecting strictly local effects and no significant extinctions.
Hm, arXiv came about because a couple of physicists were fedup with SPIRES and hacked a proper electronic preprint index and archive - of course having TeX and PS as community standards makes a huge difference.
It is there, new subfields can just start using it and set their own community expectations.
Oh, and the NSF decided it was really nifty and supported the, very small, core operation. International mirrors sprang up very very quickly.
ADS came about because NASA wanted a central repository for astrophysical data, including papers. So they paid someone to put it together, and then they decided since they had it to open it to all NASA funded researchers, and then they decided to keep it rolling and make it comprehensive, and then they decided the marginal cost of just opening it to everyone was trivial.
And they were right.
Any other similar strength player can follow suit.
NIH?