A look at diminishing atmospheric pressure
Guest post by Andi Cockroft
In an unrelated article of mine on Isostacy and Mean Sea Level posted here, I mentioned in passing a thesis paper by Theresa Cole (here) and here: ColeTheresaN2011MSc – which included this graph depicting an observed fall in global annual mean atmospheric pressure since 1916 (from NOAA I believe)
A recent exchange with Theresa, has caused me to revisit this apparent anomaly, and wonder where this is all heading – and indeed how long this has been going on !
But why the heading – So Dinosaurs Could Fly ?
Well, seems that engineers are of the opinion that the pterosaurs were just too heavy to get off the ground given today’s environment, and they must have been helped by far denser air.
Denser air of course means a higher pressure – I have seen estimates ranging from about 3.5 to 8 times that of today. Let’s pick a mid-point of say 5 for the purpose of this post. (I trust these are not the same engineers who state categorically that a Bumble-Bee is incapable of flight)
So from 100Mya to today, how has air pressure gone from a possible 5000 mbar to 1013 mbar of today? And why is it still (possibly) continuing to fall?
Questions that spring to mind are:-
· Is our atmosphere being sucked out in to space?
· Is the composition of the atmosphere changing and so getting lighter?
· Change in water vapour?
· Increasing CO2
· Burning hydrocarbons + O2 -> CO & CO2
· Volcanic eruptions
· Release/Uptake of gases from/to the ocean
· O3 -> O2
· Is an increase in temperature causing a somehow related increase in pressure?
For those who might not remember, I remind readers I do not have strong scientific qualifications in meteorology, hydrology chemistry etc., just an enquiring mind – so feel free to disagree with my arguments here.
In researching this post, I came across many conundrums. Many contradictions or seemingly incongruent theories. But hey, let’s look at what is out there starting with young Earth and work forwards to see what we shall reveal.
I also found myself using those well used weasel words such as could, may, might, suppose etc. Sorry, but given the nature of the discussion – this is just what it is a discussion of some possibilities – not proven fact!
So, just looking at the graph in figure 1 of the past 90 years:- Temperature may have localised effects, but in general, global mean atmospheric pressure at sea level is directly proportional to the mass of the entire atmosphere – the current accepted mean value is around 1013.25 Mbar. So any warming observed over the past 90 or so years should be ruled out as causation – warm or cold the air weighs the same (within reason)
A drop of 1 Mbar may seem trivial over 90 years, but at that rate mother Earth may run out of atmosphere altogether in just 100,000 years !!
Going back 100 million years, for a pressure equivalent to 5000 Mbar, there would have to be either (a) a lot more air, or (b) different composition – or a combination of each.
And of course the raging question – how has a 5000 Mbar atmosphere reduced to todays 1013.25 Mbar?
The Levenspiel et al 2000 paper is well worth a read, and has been cited indirectly here as part of 450 Peer-Reviewed Papers Supporting Skepticism of AGW caused Global Warming here, and referred to at WUWT here.
What was the air pressure for the 97% of Earth’s life before the age of dinosaurs? Levenspiel et alhave three possible alternatives, as shown in Figure 3.
- The pressure could have been at 1 bar throughout Earth’s earlier life, risen to 4–5 bar ~100 Mya (just at the time when the giant fliers needed it), and then returned to 1 bar (curve A).
- The pressure could have been ~4–5 bar from Earth’s beginning, 4600 Mya; and ~65 Mya, it could have begun to come down to today’s 1 bar (curve B).
- The atmosphere could have started at higher pressure and then decreased continuously through Earth’s life to ~4–5 bar ~100 Mya and down to 1 bar today (curve C).
The third alternative seems to be the most reasonable, so let us pursue it. We will also look into the composition of Earth’s atmosphere, but we will first discuss Earth’s surface and see how it affects the atmosphere.
From http://www.engineeringtoolbox.com, the specific gravity of some common gases can be found in the table below:
| Gas | Specific Gravity |
| Acetylene (ethyne) – C2H2 | 0.90 |
| Air1) | 1.000 |
| Alcohol vapour | 1.601 |
| Ammonia – NH3 | 0.59 |
| Argon – Ar | 1.38 |
| Arsine | 2.69 |
| Benzene – C6H6 | 2.6961 |
| Blast Furnace gas | 1.02 |
| Butadiene – C4H6 | 1.87 |
| Butane – C4H10 | 2.0061 |
| 1-Butene (Butylene)- C4H8 | 1.94 |
| Isobutene – C4H8 | 1.94 |
| Carbon dioxide – CO2 | 1.5189 |
| Carbon monoxide – CO | 0.9667 |
| Carbureted Water Gas | 0.63 |
| Chlorine – Cl2 | 2.486 |
| Coke Oven Gas | 0.44 |
| Cyclobutane | 1.938 |
| Cyclopentane | 2.422 |
| Cyclopropane | 1.451 |
| Decane | 4.915 |
| Deutrium – D2 | 0.070 |
| Digestive Gas (Sewage or Biogas) | 0.8 |
| Ethane – C2H6 | 1.0378 |
| Ether vapour | 2.586 |
| Ethyl Chloride – C2H5Cl | 2.23 |
| Ethylene (Ethene) – C2H4 | 0.9683 |
| Fluorine | 1.31 |
| Helium – He | 0.138 |
| Heptanes | 3.459 |
| Hexane | 2.973 |
| Hydrogen | 0.0696 |
| Hydrogen chloride – HCl | 1.268 |
| Hydrogen sulfide – H2S | 1.1763 |
| Hydrofluoric acid | 2.370 |
| Hydrochloric acid | 1.261 |
| Illuminating gas | 0.4 |
| Isobutane | 2.01 |
| Isopentane | 2.48 |
| Krypton | 2.89 |
| Marsh gas | 0.555 |
| Mercury vapour | 6.940 |
| Methane – CH4 | 0.5537 |
| Methyl Chloride | 1.74 |
| Natural Gas (typical) | 0.60 – 0.70 |
| Neon | 0.697 |
| Nitric oxide – NO | 1.037 |
| Nitrogen – N2 (pure) | 0.9669 |
| Nitrogen – N2 (atmospheric) | 0.9723 |
| Nitrous oxide – N2O | 1.530 |
| Nonane | 4.428 |
| Octane | 3.944 |
| Oxygen – O2 | 1.1044 |
| Ozone | 1.660 |
| Pentane | 2.487 |
| Phosgene | 1.39 |
| Propane – C3H8 | 1.5219 |
| Propene (Propylene) – C3H6 | 1.4523 |
| R-11 | 4.742 |
| R-12 | 4.174 |
| R-22 | 2.985 |
| R-114 | 5.9 |
| R-123 | 5.279 |
| R-134a | 3.522 |
| Sasol | 0.42 |
| Silane | 1.11 |
| Sulfur Dioxide – SO2 | 2.264 |
| Toluene-Methylbenzene | 3.1082 |
| Water gas (bituminous) | 0.71 |
| Water vapor | 0.6218 |
| Xenon | 4.53 |
1) NTP – Normal Temperature and Pressure – is defined as air at 20oC (293.15 K, 68oF) and 1 atm ( 101.325 kN/m2, 101.325 kPa, 14.7 psia, 0 psig, 30 in Hg, 760 torr)
Since specific gravity is the ratio between the density (mass per unit volume) of the actual gas and the density of air, specific gravity has no dimension. The density of air at NTP is 1.205 kg/m3
To change the “mass” of the atmosphere to any meaningful way would require say a 75% mercury vapour composition – something not altogether conducive to life as we know it. The alternative is of course just a lot more atmosphere.
Turning our attention for a moment to Earth’s twin, Venus, formed in probably very similar environs, yet Venus retains an atmosphere composed of CO2 and Nitrogen, with a pressure equivalent of around 90 Bar. Venus is closer to the Sun, so receives greater energy, but that cannot in itself account for the very significant differences in today’s environments.
Levenspiel postulates that the creation of Earth’s companion Moon stripped off much of Earth’s mantle, leaving it a rather fluid lithosphere compared to Venus. It is this fluid lithosphere that has allowed continental drift to rearrange and directly affect the planet’s atmosphere. Couple that with a slightly cooler Earth (less sunlight), allowing liquid water to form, and the basis for removal of CO2 is formed.
If say 4 Bya, Earth did have an atmosphere with a 90% CO2 concentration, with a high atmospheric pressure, Levenspiel proposes that simple dissolution in water would see a 50% reduction in nett CO2 atmospheric concentrations.
But it doesn’t stop there
Several cycles take place to remove CO2 from the atmosphere, not least by dissolution in rain, combination with minerals on land and ultimately flowing into the oceans and deposit as sedimentation.
True, some subduction at plate boundaries would recycle carbonates through volcanisms and back into the atmosphere, but over time a gradual reduction of CO2 takes place.
As carbon life-forms take up even more carbonates to build homes for themselves, then die and bequeath these homes to the sea floor as sediment, more and more carbon is tied up as rock.
In Potential Errors in Estimates of Carbonate Rock Accumulating through Geologic Time (pay walled here), Hay calculates that today the continents contain at least 2.82 × 106 km3 of limestone, which are the remains of deposits over the past 570 million years that have not been washed to sea or subducted back into Earth’s interior. This is equivalent to a CO2 atmospheric pressure of 38 bar. If we add the carbonates found on the ocean floor, the equivalent CO2 atmospheric pressure rises to 55 bar.
Adding all this together more than accounts for a 90% CO2 concentration at 90 Bar being reduced over time to a much lower say 20% CO2 and 4 or 5 bar – just right for the pterosaurs to take wing.
Whilst all this was going on, plant life took a turn all of its own.
Evolving from the primordial soup, cyanobacteria initially removed Iron from the oceans and created Oxygen. It was this oxygen that then led to multi-celled life-forms and ultimately diverging between the plants and animals such as protozoa, fish, land animals and dinosaurs
Above: A laminated rock formed by the growth of blue-green algae (i.e., cyanobacteria)
So, if we now accept that 100Mya, there was an atmosphere with about 20% CO2 and say 5 Bar pressure, would plant and animal life have thrived under such conditions? Do we even know that these values were anywhere near accurate?
If we believe the aeronautical engineers, pterosaurs needed a denser air to succeed – that estimate is between 3.5 and 8 times current density (=pressure). So that part of our assumption looks OK on the face of it – yes air would have had to have been more dense.
And what of O2?
Well perhaps it comes down to some type of proxies – yes our old friends !
We do know that there were some pretty impressive flying insects around back then, and it seems well known that insects breath through their “tracheae” – narrow tubes – rather than having lungs or gills. These tracheae transfer O2 directly from the surface of the skin into the organs of the body. The ability to uptake O2 is governed by the length of the tracheae. Big insects naturally have longer tracheae, so uptake less O2 – that is unless O2 is served at higher concentrations and/or pressure so the body can get all the O2 it needs.
Since we know there were huge dragonflies and cockroaches around during the Carboniferous and Permian (300-250Mya), it seems to support a postulation that O2 concentrations were of the order 35% back then, compared to today’s 20%.
Meganeura, a genus of dragonfly from about 300Mya had a wingspan of up to 65cm (2’1”), and Meganeuropsis Permiana from about 250Mya grew even larger – up to 71cm (2’4”).
Neither survived to compete alongside the pterosaurs however. Many believe the concentrations of O2 dropped too low to allow such mega fauna to survive beyond the Permian.
In Part II, I will pick up on your suggestions from comments here, and look to what has happened to reduce Atmospheric Pressure from 5 Bar to 1 Bar, and why it continues to drop today.
Brian H: There ain’t no difference nohow between pulling and pushing.
Ah, but there is. Take a look at
http://sites.bio.indiana.edu/~hangarterlab/courses/b373/lecturenotes/water/waterintro.html
Scroll down to the sections “Capillary Rise” and “Tensile Strength”. We can’t get water to the top of a 200 foot tree by capillarity or by suction (max lift c. 32 ft).
Janice says:
June 2, 2012 at 7:51 pm
Question that comes to mind: What do we not know about the pterosaurs? We don’t know if they could fly, or if they could glide, or if they had scales or feathers. We only know that they appear to resemble some of the birds that live today. Some of the birds that live today do not fly, nor glide. Some appear to use their wings to simply maintain their balance, or sometimes to help them swim. As further muddying of the water, what’s to say that the pterosaurs weren’t some sort of swimming animal?
The only nonflying birds are ones that lost flight secondarily, except possibly the ratites. The bat-like membrane wings of the pterosaurs stretched between thin fingers would be no use whatsoever in the sea, these were no manta rays. The first thing you need to understand in biology is the unity of form and function, if something looks like it flew, it probably did fly.
Or of course if they did not fly, then what purpose could these huge wing structure have played? Perhaps the pterosaurs had discovered morality, and used the large thin structures as clothing to conceal their genitals. Or maybe they had developed a taste for holidays on the beach, and evolved wings to be deployed as beach-umbrellas?
Steve P says:
June 2, 2012 at 3:40 pm
MacCready’s Q. northropi “model” was not very realistic, and proved little.
However, the model was not anatomically correct and embodied vertical and horizontal tail stabilizers that were lacking in pterosaurs. The weight distribution of the model was also different due to the longer tail of the model.
An aircraft designer’s contributions to compensate for the lack of a computer light enough (and fast enough) to make the minute corrections necessary to keep it flying. Quetzalcoatlus was essentially a B-2 — no empennage meant it was highly unstable in all three axes. It had to make dozens of small corrections every minute it was in the air, either with its wings or head, in order to stay aloft.
Unless, of course, it made a living by renting itself out as a beach umbrella…
davidmhoffer says:
June 2, 2012 at 10:23 am
Besides, he built his model out of wood and all the fossils we’ve found so far were made out of rock…
Okay, that’s it. No more popcorn for you until I get my keyboard cleaned off…
phlogiston says:
June 3, 2012 at 7:54 am
Perhaps the pterosaurs had discovered morality, and used the large thin structures as clothing to conceal their genitals.
That was actually my first thought when Steve P said that MacCready’s model was not anatomically correct…
@ur momisugly Stephen Rasey
Touche’. Thinking in terms of energy vice power.
Here’s a good paper on wing shapes at low reynolds numbers, also some discussion about power requirements. Still unsure about power requirements for soaring reptiles. Reaching minimum drag flying speed is the flight regime that requires the most power. Then power requirements aren’t as high, especially if they are “soaring designs”.
http://www-scf.usc.edu/~tchklovs/Proposal.htm#_Toc110650543
Bill Tuttle says:
June 3, 2012 at 8:35 am
Bill, that part came from Wikipedia. Not that I disagree, but at June 2, 2012 at 3:40 pm
I said this:
Period. The part in italics in my original post at 3:40 pm came from Wikipedia and my formatting should have made that crystal clear. Apparently not.
You also said that
I think that qualifies as a misleading oversimplification, at the very least, like Venus being Earth’s “twin.”
You then went on to say:
Well the B-2 may require a computer to fly – not that it is alone – but the B-49 managed to fly pretty well without one. It was the development of the deep-chord monoplane wing that allowed these aircraft to fly, not the computer.
At any rate, neither the B-49 nor the B-2 have a long neck extending forward of the wings. For that, you’d have to cite the B -70, but it didn’t have big, wide wings. It did have powerful engines however. With enough thrust (power-to-weight ratio greater than 1), even a brick can fly, but I wonder of Q. northropi perhaps tucked/folded its long neck against its breast ala Great Blue Heron when flying?
At any rate, for the pterosaurs , all that’s really required for them to fly easily is a thicker/heavier/denser atmosphere than what we have today. They had all the special adaptations necessary for flight: long wings, hollow bones – pneumatic in some cases – specialized keel bone for flight muscle attachments, and specialized brain development for flight control.
No flying bird today weighs much beyond about 40 lbs. Elephants and other pachyderms, while massive, are small compared to some marine creatures.
Video of hippos moving while underwater is revealing, and entertaining. Who knew these seemingly clumsy, awkward beasts could move so gracefully while submerged?
Phlogiston, looks like the pterosaurs may have been a lot like ducks. Ducks, if their wings are stretched all the way out, look a lot like a pterosaur, especially if you remove all the feathers. And even though ducks can fly, they are much more at ease simply floating around on shallow water and grubbing in the mud for food. Many wild ducks don’t fly much, using their wings to escape from danger by stretching them out to allow their little legs to work better for running (not really flying, but doing a very shallow glide). So I will agree that a pterosaur might be able to fly, but I would hedge on that by saying that it may never have felt the need to do so.
http://www.citeulike.org/user/martydaniel/article/6090353
Speculations on this subject should include an awareness that the diameter of the Earth itself during Pangaea was about 60% of today’s. The Earth has expanded since “antediluvian” times, whatever length of time ago those actually were.
This can be proven for oneself by getting a couple of inflatable globes. Cut one of them up, and patch Africa into the Americas, etc, and you will see the collapse as you go back in time. You can see the corkscrew that happened in the Arctic. You notice the shapes of continental edges and how they tore open as –whatever it was– happened. You see why there are mountains as wrinkling of the crust was inevitable with the diameter change.
I was introduced to this reality on a Young Earth Creationist website. This was supposedly the catastrophe that led to Noah’s Flood. But that explanation is far from the only one possible and is denied by some of the layers found in the Earth’s fossil record. It seems more likely that there have been repeated catastrophes that led to successive ages of life and fauna, or that something has been going on gradually for a long, long time, related to Wegener’s Plate Tectonics..
—–
Another relevant factor in understanding greatly different atmospheric pressure is the Gas Law equation PV =nRT, where P is pressure, V = volume, n=number of moles, T is the temperature in Kelvins or some other measure where absolute zero is zero on the scale, and R is the “gas constant,” a fudge factor that makes all the units come out right. It value will depend on what units you use to measure everything else. In the SI system of units, its value is 8.3 J per Kelvin per mole.
Using this equation for an entire atmosphere is a bit problematic, for pressure will be different at different depths and so on. But it is still relevant.
I am of the same opinion: The diameter of the Earth grows
because the gain in the Pacific is 20 cm/year and in the Atlantic
is 10 cm/year, where the continent plates drift apart… It is falsely
shown that the continental plates move downwards under
the adjacent (in California for example) plate, maintaining the globes
diameter…. but I am sure
this is wrong….
The ongoing globe expansion will also produce a atmospheric
volume expansion
with the atmospheric material thus thinning, thus less dense for
flying……
JS
Quite a mix here–brilliant comments from Phlogiston, Chuckles, and others, combined with a medley of sheer quack science–growing earth, shrinking earth (gained a following before plate tectonics), diminishing G, Noah’s flood taken seriously with other Creationist nonsense. I wonder if meteor accretion exceeds hydrogen and helium loss.
It seems to me that a wildly varying atmosphere would be as problematic to evolution as an unconstant G would be to cosmology. The distant galaxies appear to have the same gravity behavior as the near ones–none of them flying apart even when colliding–usually. Likewise an undependable atmosphere would be nearly as dangerous for life as a solar system which had not been mostly cleaned of collison debris. In a very thick atmosphere big animals could fall out of trees and off cliffs and not be hurt. Penguin like creatures could fly. Frogs would not need lungs, and amphibians might never have lost their ocean hegemony.
Land vertebrates rely heavily on precise sensing of O2 and CO2 to control breathing–it seems unlikely that such highly tuned systems have survived a roller coaster of air pressure. As with climate, there must be negative feedback systems that keep air pressure and gas mix in check. Rain drops typically fall in air with no vertical wind component, and if fossil rain drops indicate similar atmospheres, that may be as good evidence as we get for a while. –AGF
agfosterjr says:
June 3, 2012 at 2:04 pm
No one is making that argument.
@agfosterjr The distant galaxies appear to have the same gravity behavior as the near ones–none of them flying apart even when colliding–usually
While I do not accept that the gravitational constant is changing, nor that the Earth’s diameter has significantly increased in 2 billion years, I must point out that it is the “gravity behavior” of near and distant galaxies that has caused cosmologists to hypothesize otherwise unknown Dark Matter and Dark Energy.
Sorry for coming in late, but I’ve been busy. The mathematician who posted up above is quite correct. The Earth (and all of the other planets) are constantly losing atmosphere by thermal outgassing — molecules that happen to bounce just right and end up with escape speed on a trajectory that takes them away from Earth. Lighter molecules are lost faster than heavier ones — hence little hydrogen or helium in the atmosphere, while O_2, O_3, and CO_2 last a fair bit longer.
IIRC, the lost atmosphere is constantly being replenished by outgassing from the Earth’s crust and biological processes. But “constantly” should be taken with a grain of salt — the process very likely has large fluctuations associated with it as the crust turns over on time scales of tens to hundreds of millions of years, not decades. So I wouldn’t worry a lot about a short-term decreasing trend over the absolutely trivial period of humans’ ability to measure pressure in the first place. That’s almost certainly just noise on some (possibly trendless!) million-year timescale function.
Besides, long before we reach 100,000 years, humans will either be able to manipulate and replenish the atmosphere with sheer engineering or we’ll likely be extinct anyway. At any rate, by then we will arguably no longer be “human”.
rgb
Andy Smith says:
“If you increase the air density, yes you will certainly increase the lift but at the same time you will also increase the drag, meaning that that you probably have not gained a great deal. ”
Perhaps, but I’m dubious. Water is denser than air, but all kinds of creatures not adapted to flight can nevertheless swim. Not just fish, but dogs, humans, and even elephants. Lacking further argument, this armchair philosopher finds it plausible that denser air makes easier flight.
Janice says:
June 3, 2012 at 11:38 am
Phlogiston, looks like the pterosaurs may have been a lot like ducks. Ducks, if their wings are stretched all the way out, look a lot like a pterosaur, especially if you remove all the feathers. And even though ducks can fly, they are much more at ease simply floating around on shallow water and grubbing in the mud for food. Many wild ducks don’t fly much, using their wings to escape from danger by stretching them out to allow their little legs to work better for running (not really flying, but doing a very shallow glide). So I will agree that a pterosaur might be able to fly, but I would hedge on that by saying that it may never have felt the need to do so.
The long bills of some pterosaurs do suggest an ecological niche similar to a pelican or cormorant (the set of animal / bird types and corresponding niches is broadly similar in dinosaur/pterosaur times a now). They would have needed quite a substantial waterproof feather plumage in order to have floated – do you know if there is any fossil evidence for feathered pterosaurs?
mfo says:
June 2, 2012 at 6:24 am
There is a NASA project to obtain the first quantitative measurements of atmospheric pressure on the early Earth, from the Archean Eon >2.5 billion years ago:
———
Now that’s what I like to see!
I take it back. It’s the roots: they’re pushing water up the trunks, and forcing it to squirt out of the leaves.
Steve P says:
June 3, 2012 at 11:28 am
@ur momisugly me: I think that qualifies as a misleading oversimplification, at the very least, like Venus being Earth’s “twin.”
Not *that* much of an oversimplification to compare Q. northropi to a B-2, considering the Northrop connection to both…
You then went on to say: “no empennage meant it was highly unstable in all three axes. It had to make dozens of small corrections every minute it was in the air, either with its wings or head, in order to stay aloft.”
Well the B-2 may require a computer to fly – not that it is alone – but the B-49 managed to fly pretty well without one. It was the development of the deep-chord monoplane wing that allowed these aircraft to fly, not the computer.
The B-49’s four vertical stabilization fins (extending above and below the wing) served well enough to controll yaw stabilization.
With enough thrust (power-to-weight ratio greater than 1), even a brick can fly
Heh. That statement always produces red faces among my fixed-wing brethren.
but I wonder of Q. northropi perhaps tucked/folded its long neck against its breast ala Great Blue Heron when flying?
Could be — it appears to have been flexible enough to do so.
At any rate, for the pterosaurs , all that’s really required for them to fly easily is a thicker/heavier/denser atmosphere than what we have today. They had all the special adaptations necessary for flight: long wings, hollow bones – pneumatic in some cases – specialized keel bone for flight muscle attachments, and specialized brain development for flight control.
No flying bird today weighs much beyond about 40 lbs.
No dispute there, actually, but the atmosphere would have to have remained fairly dense right up through the Miocene — Argentavis magnificens is estimated to have weighed at least 150 pounds.
Amidst all this speculation about what extinct flyers could or couldn’t do I repeat, we have an extant bird which is almost universally credited with the ability to dive at 240mph (=386kph=107m/sec). So I ask, how thin would the air have to be for such a stoop to be possible? Maybe all our barometers are wrong. Or maybe Alerstam’s radar gun is right (85mph max). But I challenge any to find skeptical aerodynamic discussion of the claim. Why should we put any credence in dead bird aerodynamics when we can’t get the live ones right? –AGF
agfosterjr says:
June 3, 2012 at 2:04 pm
Your question about equilibrium status of the atmosphere amd feedback was taken up by Robert Brown:
Robert Brown says:
June 3, 2012 at 10:13 pm
It makes sense that the atmosphere isnt just running out from a static starting stock but instead is the result of an equilibrium.
More on the avian and dinosaur lung arrangement can be found here:
http://people.eku.edu/ritchisong/birdrespiration.html
The special edition on dinosaurs in the journal Anatomical Record is available at palaeoblog here – the articles are all downloadable:
http://palaeoblog.blogspot.be/2009/09/anatomical-record-special-issue-on.html
Here is Emma Schachner et al 2009 on recent evidence for dinosaurs having avian lungs:
http://onlinelibrary.wiley.com/doi/10.1002/ar.20989/pdf
The basis for my “ten times more efficient claim” is this quote on page 1505:
Respiration in Extant Birds
Lung morphology. The avian respiratory tract is
composed of two main components: the rigid gas
exchanging bronchial lungs and the nonvascularized
ventilatory air sacs (Duncker, 1972, 1974). The air sac
system permits unidirectional airflow over the paleopulmonic
parabronchi during both inspiration and expiration
(Maina, 2005). This system, enabled by the rigid
structure of the lung, provides birds with the most efficient
respiratory apparatus of any air-breathing vertebrates
(Maina, 2002). The rigidity of the avian lung and
constant volume throughout the respiratory cycle provide
the mechanical foundation for an enlargement of
the oxygen exchange surfaces into a three-dimensional
mesh network of blood capillaries 10 times larger than
the gas exchange surfaces found in mammalian lungs
(Duncker, 1974).
Bill Tuttle says:
June 4, 2012 at 4:50 am
Bill, good post. Thanks for keeping a sense of humor intact, and also for raising the question of the Mesozoic bird-of-prey A. Magnificens, with its 70 kg mass and 7 meter wingspan.
It’s interesting to talk about the airplanes, but I don’t think we should go too far with the analogy. Birds generate lift and thrust with their wings, while airplanes have separate parts for these tasks – wings for lift, engines for thrust.
Birds also employ variable geometry in their flight – easy for them being a flexible, living organism, but not so easy for machines. I don’t think man has done very well trying to build machines that mimic flapping flight, at least not big ones… In recent decades, variable geometry has been applied primarily to the engines rather than the wings.
But in a larger sense, the implications here are staggering, and I’m eagerly looking forward to Part II. As a student of life, I find WUWT serves as a virtual university, where I have the privilege of sitting in on the fascinating lectures of brilliant men as we all work to understand our dynamic planet.
And to be precise, airplane wings do use variable geometry on leading and trailing edges, and other control surfaces like the rudder, but typically, the term variable-geometry is applied to aircraft such as the F-14 Tomcat, that have swing-wings. Also, it occurs to me that some modern fighters employ a third set of variable-angle wings forward of the cockpit.
agfosterjr says:
June 4, 2012 at 8:42 am
Good question. I’ve had doubts myself that the Peregrine really attains that speed in a stoop, although it seems to be possible according to the Wiki article on terminal velocity. Falco peregrinus strikes with its talons clenched into a “fist” to deliver a blow – actually a kick – to the prey bird’s head, back, or wing at the bottom of its stoop, so I’d think that too much velocity might be dangerous for the Peregrine, and unnecessary. Golden Eagles are also said to attain speeds approaching 150 mph in a dive, but I’d like to see some precise data.
A recent study about the variability of atmospheric pressure (a poster presented by students of the Natl Tech Univ of Athens at the EGU 2012): http://itia.ntua.gr/1208/
Attempting to determine ambient air pressure based on fossil flyer anatomy and aerodynamics seems futile and unscientific. If by studying a dead bar goose you could determine how high it could fly (7 lbs at 21,000 feet), then you might be able to figure out how fast a peregrine falcon could dive (85mph), and you might set NASA, the Smithsonian, National Geographic, and the BBC straight (they all buy into the 240 mph stoop nonsense–at least NG used to). It seems the geese are not limited by aerodynamics but by oxygen deficit–the Himalayas rose up across their migration path and the fittest survived.
Of course birds have no problem flying around the Dead Sea; accordingly on our present planet flight is obtained over altitudes that range through more than a doubling of pressure. Vance Tucker’s “ideal falcon” could dive at super speed in his mathematical world. In the real world it seems they don’t. Maybe ancient air was thicker and maybe it wasn’t, but the most feeble evidence is the aerodynamic–excepting rain drop fossils. –AGF
I think the latest theory on Venus is that it is actually the result of two proto planets colliding some 500 million years ago. This also is theorized to have had the effect of moving Earth’s orbit further away from the Sun than it originally was. The theory coincides well with both the surface age of Venus, the strength of the Sun back then, the climate conditions of Earth at the time and after, and some other parameters.
So, Venus is actually a really poor analog for Earth, especially if that’s true.
We know we lose atmosphere to space though, and we know volcanism has slowed down (so less material being put back into the atmosphere), so seems highly likely that we did have a thicker atmosphere back then, which could provide more oxygen to such massive animals (even if the percent oxygen was the same, the density would have provided significantly more uptake by the lungs. Same with CO2 for plants), and allowed flight.
These theories seem to fit the facts so far.