"Thick Atmosphere" theory: anyone ever heard of this?

I got into a discussion with a co-worker on why dinosaurs were so big. After lunch I did a quick Google, and found a few pages mention a so-called "thick atmosphere" theory. Basically, it says that during the time of the really big dinosaurs, additional amounts of carbon dioxide and other gases made Earth's atmosphere much thicker, close to two-thirds the density of water. This thicker atmosphere would have been enough to provide "buoyancy" in the same way that water allows whales to be so much larger than any possible modern land animal. The theory points to larger hind legs and long tails of all large dinosaurs as more indicative of water based animals than land based.

Sounds like quack science to me, but at the same time, plausible enough to work. Thoughts?

than dry air.
Reason is water H2O is molecular weight 18, oxygen O2 is 32.

can't remember what show it was. But it helped explain why at certain times you had such huge insects.

Not sure why you think it's quack science, seems to make a lot of sense.

"seems to make a lot of sense".

x(

:wtf: :rofl: :spray:

I've been a lifelong dinosaur/paleontology enthusiast and I have never heard of the 'thick atmosphere' hypothesis.

Quite a number of more reputable websites say that this is one of the most irritating questions a paleontologist can get. It seems that, like a bumblebee's ability to fly, such large creatures are not physically possible.

:)

great size is as a buffer against temperature changes. And as a sort of predator-prey arms race that we frequently observe in evolution. As the prey got larger the predators had to get larger to cope.

Well and it was warmer, so the lizards didn't have to hang out in the sun so long

> It seems that, like a bumblebee's ability to fly,
> such large creatures are not physically possible.

i.e., the people who claim that a bumblebee is not able to fly
are too ignorant to understand how it does ...

A politer form of the above would be to refer to an apples & oranges
comparison but the honest (if blunt) approach works for me!
:hi:

with the heavier gases on bottom. If there was enough CO2 to make the air that viscous, it would probably suffocate all O2 breathers.

I vote for Junk Science.

The OP is referring to this crank: http://dinosaurtheory.com

It's junk science but not for that reason. I do not believe that the stratification you mention exists at lower altitudes (except for the occasional catastrophic release of carbon dioxide and even that is temporary).

to make the air viscous and buoyant.

That amount of CO2 would displace virtually all the O2 available.

The OP hypothesizes that there is enough CO2 to make the air viscous and buoyant.

That amount of CO2 would displace virtually all the O2 available.

As long as you sufficiently increase the pressure, it does not need to displace all the oxygen. As long as there is about one fifth of an atmosphere worth of pressure due to oxygen it doesn't matter if the pressure due to CO2 is over 300 atmospheres because there will be enough oxygen (actually, you'd have a major fuckup with the bicarbonate buffering system in air breathing organisms but that's not really related to oxygen being displaced). Of course, I just looked at the CO2 phase diagram and things get a little weird (supercritical fluid) at well below those pressures.

Of course, it's still retarded.

Of course, it's still retarded.

2/3 the density of water just ain't gonna happen.

If I remember correctly the atmosphere is rouchly 4/5 N2 and 1/5 O2. (there are other gasses, but for the sake of easy math, this is good enough.

Nitrogen has an atomic weight of 14, it is a diatomic element and therefore a Nitrogen molecule = 28 g/22.4 L (gas) at Standard pressure and temperature
Oxygen has an atomic weight of 16, it is a diatomic element and therefore an Oxygen molecule = 32 g/22.4 L (gas) at Standard pressure and temperature.

Hence 1/5 L of 02 (gas) + 4/5 L of N2 (gas) = + 1g + .29g = 1.29 g/L at stsndard Temperature and pressure.

Water (liquid form) is 1 kilogram per liter

For the atmosphere to be 2/3 as dense as water, (666g/L) the pressure of the earth would have to be higher than 516 atmospheres (and the volume of the atmosphere to be 1/516 its current size.

Now granted, that doesn't take into account the weight of water vapors, etc, but on the face of it, the "theory" is absurd.

:toast:

Why does a dog lick his own.... you know.


Why is this here and not on the Science Forum?

R/T and Science are right next to each other on my shortcut list. Sorry about this. :blush:

thought you were trying some creationist crap :-)

And anyway, baiting creationists is as much fun as trying to get a clock to tick: no effort is required and the results will be depressingly regular.

The notion being that prior to the flood all the water was held up in the atmosphere keeping harmful radiation out. The claim is this is why people lived so long back then. Trouble is it wouldn't keep just harmful radiation out. It would keep pretty much all radiation out. This includes the visible spectrum. It would be pitch black down here. And freezing. Except that the pressure from all that water in the atmosphere would pretty much crush everything and raise the temperature via compression. Life would be pretty much impossible. And that begs the question of where the heck did all the water go to afterwards.

but it sounds like something science fictiony. I could see it in a Godzilla movie!

Anyone else remember that?

Let's assume that "other gases" means something really, really dense to obtain a limit value. Maybe something like tungsten hexafluoride which would be about 13.1 g/l at STP. That would surely do the job, right? Well, not really. Two thirds of the density of water would be about 667 g/l. Of course, it would be foolish to assume STP with such an atmosphere. So what pressure would it take for a ridiculously dense example, such as tungsten hexafluoride to actually have a density of around 2/3 of water? Using Boyle's law, density would be inversely proportional to pressure giving about 51 atmospheres for the tungsten hexafluoride example (note that tungsten hexafluoride may not even remain a gas at this pressure --I have not checked).

Of course, WF6 is an extreme example meant to illustrate a densest case scenario but it does tell us that you could indeed have an atmosphere as described but that it would have to exist at a pressure greater (probably much greater) than 50 atmospheres. This would be somewhere around 300 atmospheres for CO2 (you could find such a pressure on earth right now under approximately 3 kilometers of water) or even higher for an atmosphere made out of mostly nitrogen. This would only seem plausible to a stupid YEC (assuming they even get this far in their reasoning and are not merely parroting what other YECs have said).

in that the composition of the atmosphere has changed over time, which shows up in things like maximum insect size.

Nothing dramatic enough to get near water, though, as far as I am aware.

Interesting aside on insects: They (for the sake of simplicity) breathe through their skin. As you increase the volume they take up, the surface area (and thus the amount of skin) increases slower than the volume does. If you kept increasing the volume, they would eventually have very little skin compared to amount of them (that needs to breathe) and so they would die. If you have different air, then you can get away with more volume per surface area/bigger insects. :)


Yes, insects don't have skin. I know. I was cutting out lots of stuff for simplicity.

you'd have a runaway greenhouse problem: hotter, so more H2O vapor -- but H2O is the major greenhouse gas

That is a potentially huge problem for the ancestors of any animal still present on earth: chemical reaction rates vary with temp, and different reaction rates vary differently with temperature. Thus, an organism typically has a very limited temp range inwhich it functions, because outside that range essential cellular reactions are out of sync with each other. That's why temperature regulation (warm-bloodedness) is so critically important. Any cold-blooded species would have to re-engineer itself substantially at the cellular level to cope with a planet that had a radically different temperature range than we experience today: if the average temperature were (say) 30C higher, the arthropods we find in amber would have to be radically different than modern arthropods -- and yet the amber fossils look morphologically very much like modern arthropods. I can't imagine that the necessary cellular level re-engineering wouldn't be accompanied by significant morphological differences, if such a re-engineering occurred -- so I conclude the hypothesis is likely bunk