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.
And here are some arguments for a flat earth:
http://www.earthnotaglobe.com/library/daniel_shenton_flat_earth_essay.pdf
This is another problem with Apollo hoax: the moon isn’t round either.
It’s best to consider the various ideas each on its own merits, if any.
agfosterjr says:
June 7, 2012 at 9:03 am
Good read.
It’s also true that we’ve had mammals scurrying around, diversifying, growing larger, evolving into a myriad of different forms since the extinction event 65 mya, but smart ones like H. sapiens appeared only within the last few hundred thousand years, or so.
The modern Blue Whale appears to be the most massive animal ever, but even its great size doesn’t protect it from another mammalian denizen of the deep, blue sea and that is the Killer Whale, sometimes called Wolf of the Sea, but I think Lion of the Sea is better, even though Orcas are much larger than lions. In fact, Killer Whales are not a whole lot smaller than T Rex. They eat Great White Sharks for lunch.
All that proves is what I said before: we don’t understand the pace or permutations of evolution but it does appear that endothermy – warm blood – confers significant evolutionary advantages.
A few more thoughts:
Big birds don’t land on trees to eat fruit, but they do land on big trees. Flying birds don’t land on the ground to eat bananas, but they do land on the ground to eat insects. Raptors also land on the ground to catch and eat prey they spot while sitting in those trees. When worms sprout wings, birds fly out to catch them, also from a perch. Even great fliers like Peregrine Falcons and Barn Swallows spend a surprising amount of time just sitting around, preening, singing, sunbathing, and doing what perched birds do.
Finally, convergent evolution is found from one hemisphere to the next with the New and Old World vultures being a good example, and the Hummingbirds and Sunbirds being another.
The maximum size reached by the New World Condor is very nearly matched by a couple of the Old Word Vultures such as the Cinereous Vulture.
But I agree we really don’t know why A. magnificens no longer flies, any more than we know why all the megafauna of the Americas went extinct sometime in the relatively recent past.
Maybe Andi Cockroft will help clear it up for us in Part II.
And I should note my mistake: Peregrine Falcons don’t sing.
And further one: a few birds are indeed bananivorous.
And so the question is:
If a banana falls in the forest, is it heard by a bird who’d be lured to eat it?
Apparently, yes, there are really some banana-eating birds. Oddly enough, they’re sometimes called Banana Birds, and a few of these are familiar species.
I’d read somewhere before that species known as “plantain eaters” actually didn’t eat bananas, but it turns out that other birds do, including some of our Orioles.
http://www.wordnik.com/words/banana%20bird
http://coo.fieldofscience.com/2008/04/banana-eating-birds.html
Bugs or bananas, there’s a bird who’ll eat ’em.
True, a banana makes for nutritious food for lots of different critters, but they are native to South East Asia. So a bird that evolved in tandem with bananas would be found there. I think it’s safe to say there is no symbiotic relationship between bananas and birds–that is, bananas don’t depend on birds for reproduction. But I could be wrong. –AGF
The problem with bigger things is a tricky one, how Chares realised when he agreed to build the Colossus of Rhodes.
Legend say that he was approached to build a statue half the size, and after long discussions and preliminary calculations, when he finally came with the model and agreed the price, he was asked if he would build the statue double-size at double-price and he hastily agreed.
The result was that he thus ruined himself and committed suicide after finishing the statue, not being able to pay his bills.
Whatever the truth of the story is, the point is that double height is the square of base surface and the cube in volume for the same body. We have not only huge flying dinosaurs but also walking giants, giant fern, giant insects how could they exist? All because of denser air? Or gravity is variable?
A weird theory says the Earth was smaller (the expanding Earth theory). Ok, I know it is weird, but let it be for a moment:
It explains in an original way how the continents perfectly fit on a smaller Earth 1/1.7 size which would have only 50% gravity – which would perfectly allow for the dinosaurs to thrive and run and jump, the giant insects to fly and fern to grow to gigantic dimensions:
http://www.dinox.org/index.html
The Earth grew through material accretion and maybe through cosmic neutrons bombardment. BTW, did anybody made the calculation how much substance is contained in the neutron bombardment and how deep do they really penetrate the ground?
Well I fear it has only the problem that the neutron count is much too low and the limited time since the existence of the Earth and universe are too short for the needed material accretion, or else life would be really interesting with many more meteors and a real neutron shower…
Now I stop before fabulating too much. OK not before a last link, the dinos left an egg – a cosmic egg near Saturn:
http://www.planetary.org/blogs/emily-lakdawalla/2012/05211206.html#ad-image-0
Lars….. the Earth must expand (like a baloon) and the
expansion is loosening up the Earth’s crust….the continents
thus drift all away and there is no place, where it is measured
that a continent submerges under the other…. all expansion lines
expand to the sides and no tectonic plate disappears by sliding under
the neighboring plate….this is not weird but very clear….
JS
Lars P. says:
June 12, 2012 at 1:07 pm
OK, I’ll bite (no one else is reading this).
But, but, what makes it grow? Why does all the new mass land in the ocean? Where did it land when there was no ocean? Where does it land now, or did it quit landing? Why doesn’t it land on the sun too? Or does it? If it does, why doesn’t the sun’s growing gravity draw us closer? And make us hotter? And make the year shorter? And the day longer? And burn our forests and calendars?
Neutrons are the least of our problems. This makes climate scientists look like little Einsteins, and brings us skeptics into disrepute by association. Nobody with the tiniest shred of intelligence can take such a theory seriously. Here’s a small sample of quantitative evidence for a planet of stable mass:
http://gsabulletin.gsapubs.org/content/82/4/1085.abstract:
“Daily growth increments and monthly markings on Silurian and Devonian corals and brachiopods were counted using a maximum count method. Early and Middle Silurian fossils indicate that the number of days per year during these periods was 421 and 419, respectively; the number of days per year in the early Middle Devonian Period was 410. The number of days per month has decreased from 32.4 in the Early Silurian to 31.5 in the early Middle Devonian.”
The earth slows down just a little, the moon moves out, the years and months grow longer–quite the opposite of what would happen if planetary and solar mass were growing. The earth isn’t flat, etc. –AGF
Mr. Foster: Accumulation of cosmic dust is indeed a bad
idea…. but better is that the compressed Earth solid core
is loosening up, releasing compressed gases (now found
with the fracking drilling technology….etc) and this way, the Earth
is expanding…thus Earth does not have to change its orbital
parameters….also the axial revolutions can be as they want,
this does not change the orbital flight around the Sun….
JS
Joachim Seifert says:
June 12, 2012 at 4:17 pm
JS, your explanation makes no sense: the gas cannot expand until it comes very near the surface. Gases are only compressible to the point that they reach their liquid or solid state density, which pressures are achieved at the deepest places of the ocean and about a mile down on the continents. So only the top mile could expand even a little, and of course there is no evidence for such high concentrations of gas (a mass majority?) even in the top layer. What little methane there is best explained as of organic origin.
And in the context of the other pseudoscience in this thread, where increasing earth mass has been the theme rather than increasing volume, your theory makes for decreasing surface gravity (equal mass, more distant from center of gravity). At the same time this hypothetically decreasing density at great depth would greatly increase LOD, not just a little as through tidal friction.
There’s a reason a planet’s atmosphere is on the outside rather than the inside. Being lighter, free gases float to the surface as soon as they can, very early in the processes of planetary formation (even in their solid states common gases are lighter than SiO2). Helium and radon continue to surface as the products of radioactive decay. Small amounts of hydrogen are freed as the result of chemical reactions, and escape to space with the helium. Methane formed beneath the surface as the product of fossilizing organic matter 2 or 3 hundred million years ago; most escaped but some is trapped under impermeable layers of sediment. If it were of inorganic origin it would have escaped with early accretion, billions of years ago. –AGF
agfosterjr says:
June 12, 2012 at 3:59 pm
“But, but, what makes it grow? ”
Well, you ruined the whole story with this question AGF and I was so proud of my little post. I should have said that I modelled it and my model proved it ok as only in the smaller world did the modelled dinos survive, in the bigger one they could not stand up.