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.
Steve P says:
June 4, 2012 at 8:59 am
Oops.The giant bird-of-prey Aregentavus magnificens dates from the late Miocene – not the Mesozoic – or about 6 mya, but the class Birds arose during the Mesozoic, or about 160 mya, during the Jurassic.
A. magnificens appears in artist’s renderings looking like a giant Golden Eagle. No bird that size could fly today on Earth.
Steve P says:
June 4, 2012 at 12:34 pm
“No bird that size could fly today on Earth.”
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Some serious problems here:
1) The weight of these birds is typically estimated by wing span, which is in turn estimated by the size of the tibiotarsi, assuming of course an atmosphere comparable to the present one.
2) The thicker the atmosphere the smaller the wing area is necessary to provide adequate lift for a given weight.
Accordingly the best ornithological evidence we might discover for a changing atmosphere would be an altered ratio of wing span to weight, which is of course difficult to determine from the partial and mangled fossil remains. Claims such as Steve P’s are based on a priori assumptions and circular reasoning: a thicker atmosphere should in fact lead to stubbier wings. –AGF
A couple of decades ago I read a fascinating book called “Why Big Fierce Animals are Rare” by Paul Colinvaux. The basic takeaway is that big fierce animals are rare because they sit atop the food chain and there just isn’t enough food to sustain that many large carnivores.
When I think about the thundering herds of immense herbivores from the age of the dinosaurs & the huge scale of ancient sharks and T-Rex’s, it is plain there is something fundamentally different about the amount of food available at the bottom of the food pyramid. You probably had more CO2 & O2 and a thicker atmosphere creating a richer organic soup in the oceans and faster growing plants on the land, maybe the earth weighed less and spun faster so you had slightly less effective gravity, maybe there were areas of fertile shallow marshes and seas before the continents finished breaking up… Whatever the cause, there was clearly more food available all along the line back in the Jurassic.
–
(aside)
I’m an artist. When I look at paintings of long dead animals, I’m frequently dismayed by the unlikely way the animal is arranged. Every time I come back to this thread, the Quetzalcoatlus illustration bugs me ’cause I think the way that bird is holding its neck just looks wrong. I can’t help but think it ought to be held more like the folded back position used by pelicans in flight.
agfosterjr says:
June 4, 2012 at 1:54 pm
s
It think it depends on how the bird does business. Many small songbirds have rather short, rounded wings like Chickadees, while others have long rather narrow ones, like swallows. Chickadees don’t do much fly-catching, but swallows make their living that way, so they need different types of wings, all under the same atmospheric pressure. Based on that observation, I don’t know if your conjecture has any merit, or not.
And I think you’ll look long and hard to find a flying creature with short, stubby wings, excluding the F-104, of course. True, Penguins are birds, and they have short stubby wings, but they are used for swimming, not flying. I think most marine creatures tend to have rather short, stubby fins, rather than long ones.
The long, probably narrow chord wings and other specialized adaptations of the pterosaurs must have served some function. If not to fly, then what?
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/
Dear Dimitris,
What a pleasure to see you post on WUWT! I discovered one of your papers quite by accident several years ago, and was most impressed. And I think your work on Hurst-Kolmogorov processes and climate is extremely compelling. I’m a physicist (who is currently dabbling only in climate science — random numbers and statistics and e.g. Monte Carlo simulations are more my line) and have worked with Langevin and Fokker-Planck (or more generally, Master equations) and appreciate the general idea better than most, and think there are very likely some very interesting e.g. Poincare cycles in high dimensional spaces that projectively become the stationary transitions you so beautifully describe (and that qualitatively fit the time series data!).
I’m hoping to get more people on this list to become aware of your work. In particular you might want to communicate with Bob Tisdale, who has some Sea Surface Temperature (SST) data that could all by itself be a poster child for Hurst-Kolmogorov with El Nino being a possible driver of (some of) the transitions. But the data series are too short to be able to really differentiate pure stochastic from driven in some way.
rgb
Nikolov & Zeller speculated that the decline of the planetary temperature over the 60 million years since the PETM was caused by a 47% drop in atmosperic pressure.
If they are right we should stop worrying about CO2 causing a “Runaway Greenhouse Effect” and start worrying about combating any further reduction in atmospheric pressure.
De-sequestration anyone?
The dinosaurs had a really great sense of humor. Hence there was a lot of levity, and not much gravity.
RGB, thanks for the flattering comment. I have the feeling that a better connection of (nonlinear) dynamical systems and stochastics is needed. About difficulties in differentiating stochastic and deterministic components, you may wish to see my paper “A random walk on water”, http://itia.ntua.gr/923/
Also, thanks for the kind comment in http://wattsupwiththat.com/2012/06/02/what-can-we-learn-from-the-mauna-loa-co2-curve-2/#comment-1000735
Steve P says:
June 4, 2012 at 9:54 am
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.
The term for that set of wing/control surface combination is “canard” — probably because the French claimed naming rights for aircraft parts (aileron, empennage, etc.) on the theory that it gives them more of a mystique than “fin” or “stuff that hangs off the rear of the fuselage.”
The canard configuration got its name from someone who evidently thought a few of the early aircraft using them looked like ducks in flight.
Also, thanks for the kind comment in http://wattsupwiththat.com/2012/06/02/what-can-we-learn-from-the-mauna-loa-co2-curve-2/#comment-1000735
I first ran into the preprint of your hydrology paper where you show a roughly sinusoidal curve that is statistically analyzed at three different scales. That figure alone is sheer brilliance, and should be required “reading” for every single person involved in climate research. The entire IPCC political force should be required to sit down and have it explained to them, using simple words and speaking slowly and distinctly so they cannot possibly fail to understand. Then they should be made to understand that the entire thermometric era — and quite possibly the entire last millennium — is arguably still just “region A” in this figure, since the only meaningful variability trend visible in the ten-million year data is the punctuated decline over the last 3.5 million years, with what appears to be warm/cold phase oscillations associated with strange attractors (poincare cycles) in some at least 3 or 4 dimensional phase space, projected onto global temperature. Enormously nonlinear and chaotic, with unknown feedbacks and capable of synchronizing itself to weak quasi-periodic external forcings like those provided by the general planetary orbital variables (tilt, eccentricity and so on).
Everything on top of this appears to be exotic noise — driven noise, to be sure, non-Markovian noise quite possibly, but resolving signal from the noise, causal trend from Taylor-series accident returns us once again to your figure.
I finally got a few of the better physics people who post on the list to look at your Colorado State talk (which is brilliant and so very easy to understand). And I wasn’t kidding — look up a few of Bob Tisdale’s many posts on SSTs and take a gander at his data. If perfectly meshes with the Hurst-Kolmogorov model, IMO — punctuated transitions to locally stable (on a decadal scale) states, with a POSSIBLE weak bias in the direction of transition and the period (in SSTs, they appear to weakly synch with El Nino).
Anyway, a pleasure (once again) to see you on WUWT. There are some very good discussions that take place on some of the threads, sometimes with halfway decent physics and statistics, along with a certain amount of (possibly understandable) ranting — not really terribly constructive except as an opportunity to vent against political solutions imposed by force to ameliorate a problem that has not been soundly demonstrated to exist. But focus on the science and math as sometimes it is quite good (and unlike the IPCC reports and RealClimate, a few of us try to police claims against the CAGW hypothesis that don’t hold water or are just bad science — we try to be critical of our own plausible beliefs and not just knee jerk oppose CO_2 mediated CAGW because we don’t like the idea of carbon taxes that even according to their political proponents WILL NOT WORK to significantly ameliorate the worst-case projected problem).
rgb
You’re living proof that rumours of brilliant thinkers in Ancient Greece may have some basis in fact, despite the apparencies of recent history. .
😉
Steve P says:
June 4, 2012 at 3:57 pm
“And I think you’ll look long and hard to find a flying creature with short, stubby wings, excluding the F-104, of course.”
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And I would maintain the reason is that we don’t have a dense atmosphere. If the atmosphere doubled in density a robin might take to soaring (and starve) or it might reduce its wingspan. And consider that the weaker the flyer, i.e., the lower the power to mass ratio, the longer the wingspan, as exhibited by the Gossamer Albatross.
Ashby says:
June 4, 2012 at 3:41 pm
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The biggest animal that ever lived is alive in the ocean today. –AGF
PS, if you want to see some stubby wings the Gee Bee had the Bee Gee beat all to pieces:
http://en.wikipedia.org/wiki/File:GeeBee_R2_Oshkosh.jpg
http://cdn-www.airliners.net/aviation-photos/middle/5/5/7/0575755.jpg
http://flyawaysimulation.com/media/images2/images/wolf-aircraft-cyclone-bee-gee-racer-fsx1.JPG
agfosterjr says:
June 5, 2012 at 7:22 am
Yes, marine animals can be much bigger than terrestrial ones because water is much more buoyant than air for floating bodies.
Because of water’s buoyancy, enormous marine creatures can live today, but no terrestrial beast is bigger than a bull African Elephant, an animal that can neither run, nor jump, and weighs up to 10 tons. Out to sea, a Blue Whale can weigh up to about 200 tons.
The design of terrestrial animals is different from the design of marine animals, and both differ from that of birds. To fly, birds need a relatively light-weight, streamlined body, wings to generate lift, a breastbone to attach the wing muscles, and hollow bones to reduce weight, to mention just some of their specialized adaptations for flight.
Terrestrial animals, meanwhile, must support their own weight with the structure of their bones, and there are numerous ways to do that, some seemingly better than others, but all constrained by gravity and physics.
Marine forms can become streamlined rather like a missile to reduce drag, because the buoyancy of water is providing most of the support for them, and that allows massive size.
So how did 35 ton Supersaurus manage to get around on land when an elephant can only shuffle? Some dinosaurs are estimated to be even more massive, approaching 100 tons, or more.
Similarly, no flying bird today weighs much more than c40 lbs., and the vast majority weigh much less.
You also wrote about my no stubby wings comment:
Or, the robin might just get a little bigger to take advantage of a denser atmosphere, but as you allow, an American Robin would have no reason to begin soaring, because there is no food up there for it, unless worms too someday sprout wings.
An American Robin can see potential prey much better down on the ground, where it does most of its summertime hunting for smallish insects, and neither its wings nor its tail are shaped or adapted for soaring anyway.
And that example illustrates the problem with hypothetical situations: there are too many unknowns, both known and unknown, along with the unwarranted assumptions. I work to base my arguments on empirical evidence, not theory.
As far as I know, the only songbird to soar is the Common Raven, which species is also the largest and heaviest songbird, btw. Soaring is a strategy for big birds, not small ones. Birds with long, narrow wings like the Albatrosses use them to stay aloft for long periods, and to cover great distances as they feed. The general rule is the more aerial the bird, the longer its wings, and I wouldn’t be surprised if the same rule should apply to the Pterosaurs.
Again, the design of the wing is a function of the bird’s way of making a living, and birds have many different ways of doing that. Similarly, the shape of a fighter’s wing is distinct from that of a transport because the two aircraft have different missions even though both fly in the same airspace.
So, again, based on real-world examples, your conjecture about a direct wing-size-to-atmospheric-density relationship is refuted by modern birds, who have wings short and long, but all fly in the same sky.
I don’t think we know nearly enough about how Pterosaurs made a living to object to the way their wings were conformed. There was something about their environment that prompted nature to design them that way. Perhaps early ones had shorter wings – isn’t that how evolution would work? – but most seemed to have had longish wings, and by no means were all of them large.
@Bill Tuttle: Yeah; newer canards work better than some of the old ones.
The biggest animal that ever lived is alive in the ocean today. –AGF
Ah yes, but look how far down the food chain it eats! Krill?? Where’s the drama in that? Where are the 19′ high carnivores tromping around devouring bison? I suppose we’re now the keystone predator and have outcompeted any alternative predators…
>>
agfosterjr says:
June 3, 2012 at 2:04 pm
I wonder if meteor accretion exceeds hydrogen and helium loss.
<<
On page 73 of the book: “The World’s Greatest Book of Useless Information,” it reads:
“The Earth gains about twenty to forty tons of weight each day due to meteors and other space debris landing on the surface. At that rate it would take 450,000 trillion years to double the mass of the planet.”
If we assume an average rate of thirty tons per day, then in 100 million years the Earth’s mass would change by about 1/10^10. It’s a lot, but not enough to account for a significant change in surface gravity.
Jim
Steve P says:
June 5, 2012 at 2:41 pm
And that example illustrates the problem with hypothetical situations: there are too many unknowns, both known and unknown, along with the unwarranted assumptions. I work to base my arguments on empirical evidence, not theory.
Steve P says:
June 4, 2012 at 12:34 pm
A. magnificens appears in artist’s renderings looking like a giant Golden Eagle. No bird that size could fly today on Earth.
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Utterly incompatible claims. And I might as well ask, why were there no Jurassic marine animals as big as our whales? The best reason I can think of for large dinosaur size is their superior respiratory systems, not yet equaled by the mammalian.
Why are bats nocturnal? I.e., why is there only a single species of mammal that flies by day (the fruit bat)? Because mammals can’t compete with birds, about 99% of which fly by day. Birds are superior in almost every way. Mammals were nocturnal while dinosaurs roamed; like birds, dinosaurs were probably diurnal, with poor night vision. After the dinos were gone mammals ventured out into daylight and got bigger. Of course a few birds specialized on hunting little mammals at night, and a few even compete with bats, gathering fruits and bugs at night. The oil bird in the equatorial western hemisphere even uses echo location.
Your remarkable and unexplained claim that Argentavis magnificens could not fly today is in line with the whole discussion, which has appealed to both possible and outlandish speculation. We may safely assume gravity has not changed. We may also safely assume that the atmosphere has never been dense enough to appreciably “float” either land lubbers or flyers. We don’t know to what extent atmospheric mass and composition has varied, but we can place reasonable limits on max O2 because there have been forests since the Carboniferous–they did not spontaneously combust.
Accordingly you seem to be claiming that A. mag. couldn’t fly today because air is too thin–that air was substantially denser 5mya. And your reasoning seems to be that…what? Its wings are too big? It was too heavy? I don’t know–you merely state it as an unsubstantiated article of faith, and then you say, “I work to base my arguments on empirical evidence, not theory.” When in fact the whole notion that big wings imply denser air is backwards: denser air entails greater lift per wing area.
So I repeat and refine: until evidence of systematic modification of wing area to weight is identified within various functionally continuous flyer types, we have no ornithological or zoological flight evidence for atmospheric variability. Why might A mag have gone extinct? It happened when the Panama Strait appeared with the rising Cordillera. Winds changed and new predators appeared. Maybe the pumas were too much for A mag just as they were too much for the marsupial carnivores. If a puma caught an A mag without a breeze or a cliff nearby, it could not take off. So all we need is a puma than could climb better than the marsupial predators. Another possibility is a smaller invader able to reach its eggs. –AGF
agfosterjr says:
June 6, 2012 at 9:09 am
You’re all over the place with your arguments here, but these facts remain:
Argentavis magnificens does not fly today, nor does any bird that massive. Try as you might, you can’t find one.
You wrote:
Wiki:
Or about the time A. magnificens is thought to have flown.
Birds arose much earlier, and so did Pterosaurs. I don’t understand the pace and permutations of evolution, and neither do you.
It wasn’t until cetaceans became fully aquatic that they also became massive, because marine creatures can be much larger than terrestrial ones, and both can be much bigger than flying animals, because of a law of physics articulated in Archimedes’ Principle on Floating Bodies
I said:
No, I was wrong about that, having misread 5-10 million years later as 5-10 million years ago. My flub
A. magnificens dates from c6 mya not 40-45 mya
Steve P says:
June 6, 2012 at 10:43 am
You’re all over the place with your arguments here, but these facts remain:
Argentavis magnificens does not fly today, nor does any bird that massive. Try as you might, you can’t find one.
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So what? There’s nothing as big as a mammoth or mastadon either. And nothing as big as a brontosaurus. And nothing bigger than a whale. What’s your point? –AGF
Looks like previous estimates for the weight of Dinosaurs may have been dramatically too high! From today’s LA Times “Dinosaurs weren’t as heavy as we thought, researchers find”:
http://www.latimes.com/news/science/sciencenow/la-sci-sn-dinosaur-weight-20120606,0,6506496.story
Quote:
Estimating the weight of prehistoric animals by examining their fossilized skeletons is notoriously difficult. Estimates for the weight of larger species, such as dinosaurs, can vary by a factor of three or four. Now British researchers have developed a new way to estimate weight and conclude that our previous estimates are much too high: Dinosaurs were, in fact, much lighter than we thought.
A team headed by biologist William I. Sellers of the University of Manchester used a laser scanner to compile a three-dimensional image of the skeletons of various animals, then calculated the minimum amount of skin that would be necessary to cover the skeleton. Using well-known estimates for the average density of tissue, they could then calculate the weight of the animal. When they applied this technique to animals whose weight was known, including reindeer, polar bears, giraffes and elephants, they consistently underestimated body mass by 21%, they reported in the journal Biology Letters.
The team then went to Berlin’s Museum fur Naturkunde and scanned the nearly complete skeleton of the Berlin brachiosaurus, Giraffatitan brancai, one of the largest complete sauropod dinosaurs. Using their algorithm, they then concluded that the living animal weighed 23,200 kilograms (51,150 pounds). Previous estimates for the brachiosaurus mass had gone as high as 80 metric tons, or 176,000 pounds.
“Our method provides a much more accurate measure and shows dinosaurs, while still huge, are not as big as previously thought,” Sellers said.
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Why didn’t they use flightless birds to calculate the weight vs. skeleton size? Might have ended up with an even lighter ratio…
So the math WAS off, but the problem wasn’t gravity/atmosphere, it was bad estimates of mass!
agfosterjr says:
June 6, 2012 at 12:26 pm
My point is the part about Archimedes’ Principle:
It wasn’t until cetaceans became fully aquatic that they also became massive, because marine creatures can be much larger than terrestrial ones, and both can be much bigger than flying animals, because of a law of physics articulated in Archimedes’ Principle on Floating Bodies.
Simply put, water can support heavier creatures than air because it is much denser and inherently more buoyant. The whale for example, does not have to support itself with its bones, like an elephant does, so it can grow much bigger. There are limits to the amount of bones and muscle that can be used to support a creature on Earth, and let it get around. As I say, an elephant can only shuffle because of these limitations, and it can neither jump, nor run. Its size is its primary defense, and it is about as big as a terrestrial beast can be these days.
Finally, big males of the flightless, terrestrial bird known as Ostriches can weigh well over 300 lbs., and flightless, aquatic Penguins over 75 lbs. Prehistoric Penguins were even bigger.
But for flying birds these days, 40 lbs. is about it, and most are much, much lighter.
Ashby says:
June 6, 2012 at 1:03 pm
I’ll say. The numbers quoted in that story neither add up nor make sense. Did they mean they constantly overestimated by 21%?
I noticed that too, but on further reflection I think the editor had abbreviated the science writer’s prose into virtual incomprehensibility.
But I assume the scientists first calibrated the program using known skeleton to mass ratios:
Using well-known estimates for the average density of tissue, they could then calculate the weight of the animal. When they applied this technique to animals whose weight was known, including reindeer, polar bears, giraffes and elephants, they consistently underestimated body mass by 21%, they reported in the journal Biology Letters.
If the program is consistently 21% low, then that’s useful info. Just increase the numbers by 20% and you are probably in the ball park.
If you then apply it to dino skeletons and the numbers it spits out are off by 3-4 fold compared to existing estimates, then existing estimates are probably about 3x too high.
The team then went to Berlin’s Museum fur Naturkunde and scanned the nearly complete skeleton of the Berlin brachiosaurus, Giraffatitan brancai, one of the largest complete sauropod dinosaurs. Using their algorithm, they then concluded that the living animal weighed 23,200 kilograms (51,150 pounds). Previous estimates for the brachiosaurus mass had gone as high as 80 metric tons, or 176,000 pounds.
“Our method provides a much more accurate measure and shows dinosaurs, while still huge, are not as big as previously thought,” Sellers said.
The article is ambiguous about whether the new weight estimates corrected for the 21% low algorithm, but I assume they corrected for that since they identified it prior to analysis of the dino skeletons. So, I think I understand what they were saying, but I agree the article is incoherent as published. We shouldn’t have to guess about something that central to the results being discussed.
Ugh. My html quotes didn’t work. Sorry.
We’ve had fully aquatic marine animals for half a billion years, but none as big as our modern whales, toothed or baleen. The atmosphere has nothing to do with this. But what limits a bird’s size?
Speculation that Argentavis magnificens was too big to take off without a breeze or fall is just that–speculation–but it’s possible. Bird size otherwise must take into account gigantism and dwarfism rules in general. Species trapped on islands sometimes grow big (like the Kodiak bear) and sometimes small (like extinct pygmy hippos and rhinos on Mediterranean islands). In the case of the bears their size increase may have to do with their ability to fish in the ocean, or it could have to due with sexual selection. In the case of the hippos it probably has to do with a more limited food supply: the bigger the animal, the more it eats, the more easily it starves. Small mammoths survived on Wrangel Island till less than 5000 years ago. Why were they small? They had a limited food supply and no predators, while on the mainland having a predator proof size outwieghed problems of limited food supply.
We certainly don’t want to compare birds with whales, but we do want to compare whales with fish. And the blue whale is so big because of a plentiful and reliable supply of filter food. The bigger the mouth the more it can catch. Most sharks require warm water. Having higher metabolism than most fish isn’t enough to keep them warm when their gills constantly cool them; lung breathers have an advantage in this regard. But big mammals can also overheat. Size x activity spells heat exhaustion, so gigantism and speed aren’t typically combined in mammals as they were in dinos. The dino/bird respiratory system was also a cooling system, enabling them to be big AND fast.
So what limits a bird’s or pterosaur’s size? Here are some initial considerations:
1) Available niches–big birds can’t land on leafy trees and eat fruit; flying birds don’t land on the ground and eat bananas–flight is of little advantage for such a niche. Hence,
2) The size of its prey–big flyers tend to be carnivorous.
3) The efficiency of its respiratory/cooling system.
4) The size and ferocity of its predators.
At this point it’s worth noting that these avian experiments in size extremes have been largely limited to the New World where competition with advanced placentals has been restricted in time and area–hummingbirds inhabit only the western hemisphere, like condors and A. mag. And while the hummingbirds are the most energetic vertebrates extant, the soaring birds are the most efficient energy consumers among the flyers. For whatever reasons, larger birds are more energy efficient than smaller birds, but this is clearly necessitated by the limitations of feeding and digestion–a hummingbird consumes its own weight in nectar each day, and of course the nectar is easier to digest than meat. Soaring not only saves energy but prevents overheating. And while a hummingbird is always just a few hours away from starvation–it has to “hybernate” at night–a condor is always a few generations away from extinction. These are precarious niches.
Accordingly, aerodynamic limitations constitute a part of many considerations controlling flight behavior and morphology. That a giant vulture or raptor living on the edge of existence went over that edge when its territory was invaded by North American fauna is hardly reason to suppose that the atmosphere was very different. –AGF
The reduced surface gravity of the Phanerozoic per The Gravity Theory of Mass Extinction (www.dinoextinct.com) explains why the megafauna existed, among other things.