Asteroid DID kill the dinosaurs, says new Science paper

darjeeling

There's been ongoing debate about whether the massive asteroid impact at Chicxulub, off Yucatan, Mexico killed the dinosaurs. Some have argued that the impact preceded the dinosaurs' demise by hundreds of millennia (see e.g. this thread from last year). A review in this week's Science magazine, though, reports unequivocally that it was the asteroid that slayed the beasts. The article is here for those with (paid) access; for those without, ScienceDaily's report is here.

The dispute has largely turned on the pattern of sediment deposition around the crater site. Opponents of the asteroid-as-killer theory have argued for a slow deposition of sediments lasting perhaps three hundred thousand years between the asteroid impact and the cretaceous-palaeogene (K-Pg) boundary at which the dinosaurs vanished. Those who point to the asteroid as cause have claimed that the intervening sediments were laid down very rapidly as a result of collapse of existing rocks in the impact zone.

Additionally, the asteroid opponents have suggested volcanism in the Deccan region of India as an alternative cause, but the authors of the new paper argue that the environmental impact of this volcanism was not enough to trouble the dinosaurs.

The media have reported this as the end of the story. Maybe so, though I'd be surprised if everyone will agree. Meanwhile, I'll have a closer look at the paper and see what it says in detail.

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dlofnep

Was just about to post this. I've never thought any different tbh.

Galvasean

Another (heavily disputed) theory has emerged, suggesting that the Chicxulub impact messed up the Ozone layer, which eventually killed the dinosaurs.
Read about it here.

Capt'n Midnight

Fine for KT but what about the other extinctions ?

Lets not forget that the most of the earth's surface is covered by ocean floors that are less than 150 million years old.

Chances are that most asteroid craters older than 200 million years old are gone forever.


Also http://www.newscientist.com/article/dn18655-hurtling-star-on-a-path-to-clip-solar-system.html Gliese 710 could pass through the Oort cloud in about 1.5 million years.

marco_polo

Capt'n Midnight wrote: »

Fine for KT but what about the other extinctions ?

Lets not forget that the most of the earth's surface is covered by ocean floors that are less than 150 million years old.

Chances are that most asteroid craters older than 200 million years old are gone forever.


Also http://www.newscientist.com/article/dn18655-hurtling-star-on-a-path-to-clip-solar-system.html Gliese 710 could pass through the Oort cloud in about 1.5 million years.

While it is true that a crater would be long gone, very strong evidence of a massive strike would be the presence of a rock strata worldwide containing high concentrations of iridium which was the main evidence for the impact theory. The finding of a crater was just the icing on the cake in many respects.

I think the problem is moreso that the impact card is played too often in the study of mass extinctions. . At one time a massive strike was a theory put forward as the main cause of the the Permian exinction, with scant enough evidence IMO, mainly some localised iridum and quartz deposits (in Australia I think), that was eventually established as volcanic in origin. In the rocks of the correct age for the end Permian mass extinction there is simply no evidence of any unusual iridium/shocked quartz concentrations worldwide that would suggest a massive metor strike. More recent evidence suggests that the impact theory proposed as the cause of the the demise of American megafauna about 12000 years ago looks set for a similar fate as well.

Actually if you are you are interested in this sort of stuff, a great book on the Permian mass extinction is 'When Life Nearly Died: The Greatest Mass Extinction of All Time' by Michael Benton.

Galvasean

A mass extinction in 1.5 million years huh? Time to start predicting future animals so.


I must agree with Marco here. 'Asteroids did it' seems to be the kop out idea for mass extinctions. Like, when we cant decide what happened, let's just say it was teh meteors until someone figures out something better.

Galvasean

Research in Catalan (Spain) supports rapid dinosaur die off as opposed to gradual die out:
http://news.discovery.com/dinosaurs/dinosaurs-did-not-gradually-die-out.html

marco_polo

(The asteroid just helped a little bit according to Dr Prauss).

http://www.sciencedaily.com/releases/2010/03/100326124654.htm

"The resulting chronic stress, to which of course the meteorite impact was a contributing factor, is likely to have been fundamental to the crisis in the biosphere and finally the mass extinction," says Michael Prauss.

....

Based on an analysis of the appearance and distribution of organic-walled microfossils such as Algal cysts, pollen, and spores of terrestrial plants, Prauss shows that significant and persistent variations in the ecosystem of the Upper Cretaceous started long before the meteorite impact. Among others, these are reflected by fluctuations in sea-level and marine algae productivity.

Prauss also considers it highly problematic to equate the meteorite impact with the position of the Cretaceous-Paleogene boundary: "The actual impact took place well before the geochemically and micropaleontologically defined Cretaceous Paleogene boundary." He supports his assertion with the position of the so-called fern spike, an episodic, significant increase in the proportion of fern spores caused by the pioneering phase of ferns in repopulating landscapes of destroyed ecosystems. In all sections of the investigated area the fern spike occurs well before important stratigraphic evidence for the Paleogene.

darjeeling

marco_polo wrote: »

Asteroid DIDN'T kill the dinosaurs, says new paper
(The asteroid just helped a little bit according to Dr Prauss).

Looking back at the paper in Science, the authors do address the salient points in this new paper.
E.g.:

Faunal and floral changes during the Late Cretaceous do occur [e.g., (12, 47)] but are clearly distinguishable from the abrupt mass extinction and ecosystem disruption coincident with the K-Pg boundary, as indicated by high-resolution records of marine planktonic microfossils and terrestrial pollen and spores (12, 13, 25, 37, 55, 57).

and

On land, the loss of the diverse vegetation and the onset of the fern-spore spike following the K-Pg boundary indicates instantaneous (days to months) destruction of diverse forest communities coincident with deposition of ejecta from the Chicxulub impact (fig. S17) (12, 37, 55). A shutdown of photosynthesis because of low light levels is also indicated by high abundances of fungal spores in a thin layer of sediment preceding the recovery succession of ferns at a New Zealand K-Pg boundary site (56)

So experts disagree. What to think? If science were done by vote, the asteroid crowd would carry the day. Would it were so simple! As it is, this one will run and run.

Galvasean

So now the asteroid did kill off the dinosaurs...
http://www.sciencecentric.com/news/10052562-scientists-conclude-asteroid-ended-the-age-dinosaurs.html

dlofnep

That bastard asteroid. Killed off the coolest things that ever existed!