Naked Science Forum

Non Life Sciences => Geology, Palaeontology & Archaeology => Topic started by: thedoc on 07/02/2013 22:46:00

Title: Did the Chicxulub crater kill off the dinosaurs?
Post by: thedoc on 07/02/2013 22:46:00

A team led by Paul Renne at the Berkeley Geochronology Center in California have shed new light on the asteroid impact that is believed to have wiped out the dinosaurs, 66 million years ago.

Read the whole story on our  website by clicking here (http://www.thenakedscientists.com/HTML/news/news/1000076/)

  

Title: Re: Did the Chicxulub crater kill off the dinosaurs?
Post by: CliffordK on 08/02/2013 06:36:04

I had heard that the decline of the dinosaurs had likely begun prior to the Chicxulub asteroid impact, so the theory that the asteroid was merely the final nail in the coffin makes sense.

I was comparing atmospheric CO₂ and Atmospheric Oxygen.
Charts from Wikipedia:
http://en.wikipedia.org/wiki/File:Phanerozoic_Carbon_Dioxide.png
http://en.wikipedia.org/wiki/File:OxygenLevel-1000ma.svg

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Somewhere BEFORE the KT boundary/extinction event, atmospheric oxygen concentrations peaked, and CO₂ levels dropped to below 1000 ppm (0.1%).  It is  now below 400 ppm, or 0.04%.  Oddly, both the CO₂ and the Oxygen levels have declined over the last 70 million years.

There are three types of photosynthesis, C₃, C₄, and CAM. (http://wc.pima.edu/~bfiero/tucsonecology/plants/plants_photosynthesis.htm), with the primary plant growth now being either the C₃ or C₄.

The two types of photosynthesis have different growth efficiencies with respect to CO₂ concentration (http://buythetruth.wordpress.com/2009/06/13/photosynthesis-and-co2-enrichment/), with the C₃ photosynthesis favored at concentrations above 700 ppm, and C₄ photosynthesis favored at concentrations below 700 ppm.

(https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fbuythetruth.files.wordpress.com%2F2009%2F06%2Fphotosyntheticrates.jpg&hash=c502b770b94d0db584ef1ec61986f362)

Anyway, I would wonder if the event triggering the decline of the dinosaurs was not temperature, but rather a massive decrease in plant growth due to a decrease in CO₂ concentrations.  Less plant growth would have led to less CO₂ being converted into oxygen, corresponding to the observed decrease in oxygen concentration (less O₂ formation).

The megafauna, for example the sauropods would have been hard hit, but a decrease in the growth of plants could have had repercussions throughout the food chain, and both on land as well as in the water.

This article suggests that it may have been a combination of the high oxygen levels as well as the diminishing CO₂ levels (http://jxb.oxfordjournals.org/content/52/357/801.full.pdf) that impeded C₃ photosynthesis plant growth just prior to the KT boundary and leading to the KT extinctions, as well as favoring plants with C₄ photosynthesis.