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.
Correction to penultimate paragraph: “mega flora” would be large plants; you probably want “mega fauna”.
I’d like to see the model that these ‘engineers’ used to determine how pterosaurs flew. Do you have a link for it?
See, there are some details of the fossil record that strongly suggest these ideas of pterosaurs needing ‘higher air pressure’ don’t hold up. Other much smaller flyers, contemporary with pterosaurs, show adaptations for flying that suggest the air then was pretty much the same as air now. Birds in particular. All flying birds, large and small, have a feature called an alula on the leading edge of the wing. It adds wing area and increases lift during low-speed maneuvering like landing. The first known bird with an alula dates back to about 131 million years ago – the mid-Cretaceous. Birds with alulas are also known from 115 million years ago – not that long before the 100-75MYA window talked about in your source. And of course, birds from after that time also have alulas. If air pressure was that much higher, conferring that much additional lift, then why did these early birds need an alula?
Biomechanics analyses are notorious for being nonlinear — that is, small changes in the input can lead to enormously out-of-proportion changes in the results. I know that people have built pterosaur-shaped drones that fly quite well in today’s atmosphere. I also know that Don Rumsfeld’s much-mocked quote about knowns and unknowns applies strongly to prehistoric lifeforms. There are things we know, and things that we know we don’t know, but there are also things that we do not know we don’t know. There are also an awful lot of things we think we know, but ain’t really so. The fossils don’t tell us everything, and we should not ever assume that they do. As a result, I simply don’t trust esoteric analyses like this that arrive at extraordinary results.
The story of Noah and Noah’s ark is being told in many nations and peoples as a legend. Nevermind the apparent variations in the story from people to people, due to the fact that it is being told so universally all over the world, would seem to suggest to me that there was a time in the past when part of the whole atmosphere came down on us. Noah reports that after the big flood he saw a rainbow for the first time in his life. That would seem to suggest, as reported by others even earlier, that life existed without rain or snow falling down. Deposits of coal found in Antartica seem to support this argument.
So apart from blaming high CO2 – although I do not deny it is a good possible factor – I would definitely also investigate the possibility of a much higher water vapor content in the atmosphere.
The assumption of 5000 bars seems plausible to me – it explains that conditions for life were much more favourable for living longer and being bigger as well. That explains the exisitence of a certain town in south America as well that is still raising many eyebrows to this day. It might perhaps explain Stonehenge as well.
Increasing gravity??? I don’t think so. The film clip appeared sensible for about 12 mins. then went haywire. Where did all the extra material come from? Why did we not loose all atmosphere 300Ma ago since it is gravity that holds the atmosphere in place?
Makes sense to me. I would be utterly surprised if atmospheric pressure had not been higher than present. To be honest when I think of the early Hadean era Earth I always picture it with a 90 bar atmosphere, just like Venus.
I just never really considered the implications or rate of a declining atmospheric pressure and the modern world we live in… It’s funny how a person can have two different modes of understanding. The one that you live in everyday, and the theoretical… and every now and then you bang the two together in an epiphany and go “D’oh, I shoulda realized that!”
So if the theory is correct, there are some very interesting implications concerning CO2’s non role as a climate driver for starters, and it becomes more of a concern as to how long life sustaining amounts of CO2 remain in the atmosphere coupled to a decent atmospheric content/pressure.
I look forward to the second part of this post….. Interesting stuff!
Raindrop impressions and air pressure from 2.7 billion years ago.
http://www.sciencedaily.com/releases/2012/03/120328135928.htm
I have some rocks with ripple marks and raindrop impressions from 3.5 billion years.
The “bumble bees can’t fly” canard just won’t die. Here’s the absolutely true story I found on the somewhere Internet, or someplace else. I’ll provide a citation some time. Honest.
Engineers at one of the large aerospace firms were working with a computer program designed to analyze the efficiency of jet aircraft wings. Keep in mind that fixed-wing aircraft are gliders, aerodynamically–as opposed to birds and bugs which use their wings for both thrust and lift.
A bee invaded their space, and got swatted. Somebody got the bright idea to measure the bee-corpse’s wings and plug that information into the program to see what popped out. Clearly this is far outside the program’s design parameters.
The program’s output actually meant that bumble bees can’t glide. Which is true, but that’s probably pure coincidence.
Anthony is correct, temperature cannot change the total mass (and therefore the average surface pressure) of the atmosphere. It DOES change it locally, though, but vertical circulations and horizontal redistributions of mass are involved, for example, low pressure formation in one region must be matched by higher pressure elsewhere.
Also, don’t confuse density with surface pressure. Water vapor is less dense than dry air, but if you add more water vapor to the atmosphere, the surface pressure will go up. It’s like adding a log to a bathtub full of water…the log is less dense, but the total weight increases.
I tend to think that it is the existence of life which has sucked almost all of the CO2 out of the atmosphere, since Mars and Venus have atmospheres which are almost 100% CO2. But I don’t have an opinion regarding how high atmospheric surface pressure was in the past. Not enough data. 🙂
So Dinosaurs Could Fly !
Sure, and just like us, they preferred 1st Class (but the leg room in Coach was h-u-u-ge compared to today). ;o)
The wild card I’d think would be what happened to our atmosphere as the earth encountered other stellar systems while we’ve been moving about the universe. Depending on the encounter, the earth might add to its atmosphere or have some of it stripped away.
Now if you would propose that a decreasing atmosphere might be harmful to humans or a national security risk, there just might be a very large grant coming your way. I believe the equation (known as the Hansen equation) is:
h-d+F=$
where h is hypothesis, d is data and F is fear.
While many people laugh at the “expanding earth” theory (just like some laugh at AGW skeptics) – simple logic says this…. each day, tonnes of dust and micro meteroites fall to earth. I`ve seen some estimates that claim up to 200,000kg per day. If it`s 100 tonnes per day (100,000Kg), then in just 1 million years, this equals 36 trillion Kg. Now if the “100 tonnes” per day is actually more like 1000 or 10,000 tonnes per day ( we have no accurate measure)…. then the expanding earth theory has some validity. We ALL know that the planets formed by accretion of dust and rock…. why do we assume this just magically stopped 4.5billion years ago !! Of course it slowed down to an almost stop – but it could not have stopped completley. Obviously some of the crazy “expanding earth” theories that claim earth has doubled or tripped in size are crazy, but if you do the possible numbers, then it`s quite plauside that a 10-20% increase in the past billion years may have happened.
“which included this graph depicting an observed fall in global annual mean atmospheric pressure since 1916 (from NOAA I believe)”
Oh Oh! Mr. Watts: Can you remember this link: http://wattsupwiththat.com/2012/06/01/phil-jones-gives-a-talk-at-knmi-in-de-bilt-meanwhile-temperature-and-paleo-researchers-are-still-blowing-off-data-requests/
I am looking for the source of that graph and cannot find it on NOAA or anywhere else so far. You have to produce a credible source for that graph and data.
Now I have the feeling that Cole 2010 made that graph up.
Besides Cole 2010 cannot open in Internet Explorer as well as in Google Chrome. It gives warnings that downloading this file could seriously harm or damage my computer. So I won’t open it.
Please would you give us the link on NOAA or from any other harmless scientific organisation so I can verify that this graph is not fictional!
It is a very interesting piece however.
REPLY: Your paranoiaware is probably set too high on your computer. I had no trouble downloading the Cole PDF file, stored at Google docs. Since you’ve demonstrated you probably can’t get past this limitation (or won’t), I’ve placed the file on the WUWT server and updated the link. The post is by Andi Cockroft in New Zealand.
Note that the difference here is that I solve the problem rather than writing back “Why should I make the data available to you, when your aim is to try and find something wrong with it?” like Dr. Jones did. – Anthony
wolfwalker says:
June 2, 2012 at 4:16 am
I know that people have built pterosaur-shaped drones that fly quite well in today’s atmosphere.
Radio-controlled models, actually. Aircraft designer Paul MacCready built and flew a half-scale Quetzalcoatlus in 1986.
http://www.sciencenews.org/view/generic/id/338224/title/Soaring_pterosaur
Carl Chapman says:
June 2, 2012 at 12:47 am
I had an email discussion a few years ago with Steve Nerem of the Colorado Uni, which is where the sea level numbers come from. I had noticed that all the increase in sea level came from the adjustments due to global average atmospheric pressure. Without the adjustment the sea level was falling. ,,,,,,,,,,,,,,,,,,,,. The fact that the University of Colorado showed more sea level rise after the adjustment means, IMO, there is something wrong with their adjustment process and it is exaggerating the sea level rise.
========================================
exactly…..measurements show sea levels falling……adjustments/math/assumptions show sea levels rising
“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 !!”
Yes but how many years until humans expire b/c of lack of air pressure. Or will we all be wearing spacesuits 24/7 by then? This could be Algore’s new cause.
There are two periods when, at least, oxygen was significantly higher. The Cretaceous, 100 MYa 29% and the Devonion/Carboniferous, 400 to 300 MYa at 30% (briefly 35%) which made for higher air pressure.
This also allowed for giant insects in the Carboniferous for example. Giant spiders, giant dragonflys. One of the more interesting things it also allowed for was giant forest fires. With oxygen over 30%, forest fires were unstoppable and could burn half-way across a continent. Some of the coal is really just repeatedly burned-down forests.
Figure 1 looks very much like a proxy for atmospheric temperature, excepting the 1970s and 1980s. Which fits with my theory that the measured surface warming during that period was a spurious signal from increased solar insolation, due to decreased anthropogenic aerosols and didn’t result from increased atmospheric temperatures.
Any idea on what stations were used and are they the same??
Agree with Les Johnson that it’s not clear that this is guest post.
I can see AW’s small-minded foes getting their tight tights in a twist and flailing away in a twittering frenzy over this passage…
REPLY: My error, now repaired. This is in fact a guest post by Andi Cockroft, but he put his home address etc at the top along with his name and I deleted the whole lot, neglecting to put his name back. My excuse is that it was late at the end of the week when I composed the post – Anthony
I think the increased oxygen levels are a more likely reason for the mega fauna. That would explain the size of the dinosaurs. They were essentialy supercharged. It might also explain their extinction if they weren’t able to adapt to a lower oxygen level.
Since Venus is closer to the sun and smaller you would expect that the solar wind would have stripped more of it’s atmosphere than Earth’s. The moon was also closer to the Earth in the past so could it also have caused more striping of the atmosphere?
Ok, notwithstanding the pterosaur vs dinosaur discussion, we don’t know that the large versions could actually fly. Just because they were built sorta like birds, and looked sorta like birds, doesn’t mean they could actually fly like birds. Evolution and hybrid vigour being what it is, there is just as good a chance that the biggies were no different ecologically than modern counterparts: flightless, maybe a little gliding, probably mostly evolutionary dead-ends – literally, the down-side half of the foodchain. We simply don’t know if the flight crew evolved out of the big dummies, or the other way around. You could argue either, and it wouldn’t surprise if both were true.
There is this unfortunate characteristic of physical scientists to pretty much always misunderstand the range of adaptiveness built into complex organisms (trees, pterosaurs, climate scientists) as a result of their evolutionary progress. This would have been substantially true millions of years ago as it is today. It is an unwarranted and naive assumption to assume that old necessarily means primitive in terms of adaptability to their environment.
Vukcevic,
Interesting graphs, what do you think happened in the1920s? It seems an event or collection of such kicked off about then. Similarly something happened in 1972 and 1992/3. What?
Once a “particle” of air reaches escape velocity, ~18k mph, and has a clear shot, it can leave the earth’s gravitational well permanently. Surely energetic particles or photons from the sun would be capable of washing some percentage of the atmosphere from the earth.
Then there is that whole business about the speed of light not being constant. If that’s possible, maybe God decided to change the gravitational constant one morning when he discovered his design bureau had super sized some reptiles beyond accepted design limits.
I believe gravity is increasing. Everyone I know, including myself, weighs more now than 20 years ago. 🙂
Besides whether pterosaurs could fly, there are also questions about whether large dinosaurs could breath while standing in deep water. From paleontologist, Donald Prothero:
http://www.skepticblog.org/2012/04/04/bad-science-journalism-101/