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There is a site by David Esker named Dinosaur Theory: dinosaurtheory.com. David says that dinosaurs was so big because the early (at dinosaurs age) earth atmosphere was very dense and most mass of extinct giant reptilians and other non-avian dinosaurs was compensated by Buoyancy force from air.

http://www.dinosaurtheory.com/solution.html

the Earth's atmospheric density during the late Jurassic period can be calculated to be 670 kg/m3. This says that to produce the necessary buoyancy so that the dinosaurs could grow to their exceptional size, the density of the Earth’s air near the Earth’s surface would need to be 2/3’s of the density of water.

And he says that now at sea level "air has a low density of only 1.29 kg/m3". Thanks to Dikran Marsupial, 670 kg/m3 is very high, like density of some light wood types.

I have some doubts about so dense (thick) atmosphere and my question is: Is there any scientific evidence of Earth's atmosphere density in the era of dinosaurs?

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  • Related Question: Did the Earth have so little Oxygen that dinosaurs couldn't exist.
    – Oddthinking ♦
    Jan 10, 2014 at 14:07
  • Oddthinking, yes the question is related, but different. He asks about O2 partial pressure, and I asks about total air pressure.
    – osgx
    Jan 10, 2014 at 14:38
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    Oh, I didn't mean it was a duplicate. Just 'if you are interested in this proposed solution to the "dinosaur problem", you may also like...'.
    – Oddthinking ♦
    Jan 10, 2014 at 15:16
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    I'd love to see an extension of this theory: that the atmosphere was so dense that dinosaurs could float like blimps! Then, I'd love to see it made into a movie :-)
    – Nate Eldredge
    Jan 11, 2014 at 20:24
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    One should probably look at all the stuff in that time that could fly and e.g. their wing sizes. If a pterodactyl needed almost a meter of wing size, either it must have been very heavy, or evolution must have been extraordinarily generous to provide it with so much more than needed for that "air" density
    – PlasmaHH
    Nov 17, 2014 at 12:31

2 Answers 2

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Esker has no evidence to support the idea of the Earths atmosphere being more dense in the Jurrasic than it is now, other than the assertion that dinosaurs are too large to have existed otherwise. However this assertion has little support, as evolutionary adaptions (such as the unidirectional breathing discussed in the previous question) are able to explain the size of giant hebivorous dinosaurs seen in the Jurassic, without the need to introduce bouyancy from a dense atmosphere. Resource availability seems to be more of a limiting factor on size than gravitational issues.

See e.g. Saunders et al. "Biology of the sauropod dinosaurs: the evolution of gigantism" Biol Rev Camb Philos Soc. 2011 February; 86(1): 117–155. www

Also, allometry suggests that the ratio of the long bone dimensions and plausible body weight of dinosaurs is similar to that of modern animals.

P.S. you do have to wonder about anybody that refers to themselves in the third person "Esker’s Thick Atmosphere Theory violates no property of science. It is the correct solution." in supposedly scientific writing! ;o)

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    There isn't any ice on the planet nearly old enough to hold air from the Jurassic, and the gasses in lava are dissolved gasses that come from inside the mantle, not from the atmosphere.
    – user18604
    Jan 10, 2014 at 16:21
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    Lava may record atmosphere too: "Vesicular lavas preserve a record of paleopressure at the time and place of lava emplacement" geology.gsapubs.org/content/30/9/807.abstract geo.mtu.edu/~raman/papers2/SahagianJG.pdf
    – osgx
    Jan 10, 2014 at 16:28
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    Very interesting, I stand corrected; of course the air in the lava bubbles isn't atmospheric, but the size of the bubbles would depend on ambient pressures.
    – user18604
    Jan 10, 2014 at 16:46
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    Thinking about this, volcanic pummice has a density of about 640 kg/m3, so if Jurassic air density was 670 kg/m3, then pumice would float... in the air! As would a lot of vegetable matter, such as any wood less dense than mahogany, which rather suggests that Jurassic air density was perhaps unlikely to have been that high! ;o)
    – user18604
    Jan 10, 2014 at 17:04
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    Dikran, there is new article nature.com/ngeo/journal/v9/n6/full/ngeo2713.html "Earth's air pressure 2.7 billion years ago constrained to less than half of modern levels" - Nature Geoscience 9, 448–451 (2016) doi:10.1038/ngeo2713. They did it with bubble's size: "... we calculate absolute Archaean barometric pressure using the size distribution of gas bubbles in basaltic lava flows that solidified at sea level ~2.7 Gyr"!
    – osgx
    Jul 20, 2016 at 0:40
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The claimed air density is about 520 times higher than air denisty now. This means that, according to the ideal gas law, you need 520 times the air pressure - roughly 520 bar.

Now the critical point of nitrogen (main consituent of air) is about 33bar, the critical point of oxygen about 50 bar. Both critical temperatures are far below 0°C. So at this density, the athmosphere would be a supercritical fluids. Most importantly that means:

It can effuse through solids like a gas, and dissolve materials like a liquid.

So, to sum it up, with a little bit of knowledge about physics we can show that gases behave radically different before we are close to the pressures described. Whoever claimed an athmospheric density of 670kg/m³ did not think the physics side through.

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    Thank you mart! Venus has supercritical atmosphere ("93 bar... 735 K ... making the surface atmosphere a supercritical fluid") without any visible side-effects: youtube.com/watch?v=qRGTk0KQhf4 Are there scientific papers saying that Earth atmosphere was not supercritical fluid 300-50 Ma ago?
    – osgx
    May 6, 2014 at 13:04
  • @osgx Are there any scientific papers that say that Earths atmosphere was NOT a supercritical fluid? You mean aside from the full body of physics as it currently exists? Science assumes something is NOT the case unless you have evidence that shows otherwise. Since there is no science that shows that the atmosphere WAS supercritical fluids, we don't ASSUME it was.
    – Everett
    Apr 3, 2016 at 20:31
  • @osgx Actually, it is science fact that Earths atmospher was exactly like Venus. It was a 90+bar and 98% Co2. Where do you think all the Carboniferous rocks came from?. The Co2 has been sucked out of the atmosphere by orgasims and locked up in rocks, so the pressure has been dropping continuously over time. Atmospheric Co2 is currently the lowest it has ever been in geological history. If it reduces much more, plants will not be able to photosynthesis.
    – Andy k
    Mar 29, 2017 at 22:20
  • @Andyk, Welcome to the skeptics. Unreferenced claims requires scientific (published in peer-reviewed and cited) references here. When this 90+bar was, was it in the "late Jurassic period" (as in question) or earlier or later? Unscientific wiki claims that en.wikipedia.org/wiki/Carboniferous period had ONLY "Mean atmospheric CO2 ... c. 800 ppm", not anywhere near even 1% (nor 98%). And just think about how carbon-fixating organism may live on the planet with the supercritical atmosphere; and how it is possible to have "like Venus" atmospheric temperatures and Earth life at same time
    – osgx
    Mar 29, 2017 at 22:51
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    I certainly tread in caution here, perhaps I'm missing something, but since $P={rho}RT\M$, shouldn't a density increase be balanceable not just by P increase (as noted)... but also a T decrease or an M increase?? So it wouldn't be a straight 520 bars per se.
    – JeopardyTempest
    Aug 14, 2017 at 9:14

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