So Dinosaurs Could Fly ! – Part I

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)

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Figure 1 Historic global annual mean atmospheric pressure at sea level between 1916 and 2007

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 ?

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Figure 2 – Artists impression of Quetzalcoatlus with its 45’ wingspan

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 !!

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Figure 3 Three possible alternatives for the atmospheric pressure early in Earth’s lifetime, given that it was at ~5 bar, ~100 Mya.

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.

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Figure 4 History of deposition of CO2 as carbonates. The red area represents continental deposits that “float” on denser material and are not subducted. The blue area represents ocean deposits. These are frequently subducted and therefore relatively young.

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.

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Figure 5 Progressive lowering of CO2 pressure due to carbonate formation and deposition on Earth’s surface.

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

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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 !

clip_image013We 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.

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I wonder how much fluids have been lost to space from Earth over the last Billion years or so.

Dodgy Geezer

We are running out of air!
Quickly – we must convene a UN-supported set of conferences and get all the citizens of the world to breath less. Breathing more rapidly than one breath every 8 seconds will be an offence – or maybe we could simply tax people on their breathing rate….
We had wondered when they were going to tax air – it looks like the time has come….

Glenn

Perhaps this change in global atmospheric pressure has affected sea level.

Oh, dear. You’ve also opened the dual cans of worms that Venus is actually a new “young” planet (@10K years by some catastrophists’ estimates) still cooling and losing atmosphere, and that gravity has increased since dinosaur days (which would account for massive critters that apparently couldn’t survive today.
Note that I do not subscribe to either idea; just pointing out that moderation is about to get interesting. (On the bright side, I don’t think “chemtrails” can figure into this. [grin])

Carl Chapman

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. Each depth reading must allow for the local atmospheric pressure, as a low pressure will increase sea level at that point and a high local pressure will push the water out of that area, decreasing the depth. To determine whether the local pressure is above or below global average, you have to know what the global average is. They assume that the global average is changing over time, and work with that changing number.
The point I was trying to make to Steve Nerem is this: If the satellites take thousands of readings per day, then they will be taking some readings where the pressure is low and some where it is high. The adjustments for local pressure must therefore cancel out. The adjustment for local pressure compared to global average should make no difference because over thousands of measurement they have to average out.
Steve Nerem couldn’t see my point and I didn’t have the time to analyse what is wrong with the adjustment process.
I maintain that if you take thousands of measurements all over the globe, the average pressure at those places must be the global average pressure, and the average adjustment due to local pressure must be zero. 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.

Andrew30

2006 – 1916 = 90
1008.6 – 1002.2 = 6.4
Since we know that climatology operates in liner straight line trends (sea level since xx, temperature since xx, sea ice since xx, CO2 since xx, etc) and the atmosphere is a major factor in climatology then the liner straight line is the correct method to use for paleoatmosphereology expraolationology.
The trend is 7.1 per century.
Dinosaurs existed 230 million years, or 2,300,000 centuries ago.
7.1 per century times 2,300,000 centuries equals 16,330,000.
So the global annual mean atmospheric pressure was 16,331,002.2 Exactly!
The Dinosaurs actually walked on the outer edge of the atmosphere. However their methane emissions diluted to atmosphere to the point that the surface tension could no longer sustain their weight. Like a needle in a glass when the surface tension is broken, they came crashing down to earth with incredible velocity.
This is why we find dinosaurs a) Flattened, and b) Deep under the surface of the Earth. The location and condition of their remains proves the above paleoatmosphereology expraolationology.
Please refer to the respective national archeological theologies for the raw data.
Mike

Ville

How about burning hydrocarbons´hydrogen sucks oxygen out from atmosphere and turns it into water.

steveta_uk

I assume this is by Andy Cockroft – you seem to have missed the by-line.

Andrew30

“So Dinosaurs Could Fly !”
They still do, but now we call them birds.

Graeme M

A couple of sites relevant to this question… Just another take on it.
http://www.dinosaurtheory.com/index.html
http://milesmathis.com/atmo.html

Rosco

One would suppose that it is not improbable that the solar wind and magnetic activity could act to remove some of the outer atmoshere. I seem to remember eading as a child that air entrapped in an Egyptian tomb had ~ 2% more O2 than current air.
A primordial atmosphere could also have contained more longer cgain hydrocarbon gases, perhaps even some aromatics although these tend to be more toxic.
Co2 in greater concentrations seems a logical proposal but doesn’t that mean the Earth died due to the runaway greenhouse effect ?? (Actually I do not believe that hypothesis at all.)
Also a denser atmosphere would mean there is no faint young sun paradox as the adiabatic lapse rate would be greater and the tropopause would be higher in the atmosphere – does this sound right as I believe a huge atmosphere is the reason for Venus’ high temperatures due to very high compression of the atmosphere ?

Les Johnson

eyeball 1.0 suggests that air pressure is related to temperature. Which it should be. But, which drives which?
I would be interested in seeing if solar UV matches the pressure. UV driving the stratophere height….

Steve Allen

“Is an increase in temperature causing a somehow related increase in pressure?”
Don’t you mean “decrease” in pressure?

Duncan B (UK)

Am just about to settle down to read Theresa’s paper over a cup of tea and a slice of toast (liberally spread with Marmite) but I do like your thinking…..

Change in the Arctic’s atmospheric pressure is a good indicator of the future temperature changes in the lower latitudes
http://www.vukcevic.talktalk.net/AMO.htm
including the long term North Atlantic hurricane activity
http://www.vukcevic.talktalk.net/AHA.htm

Les Johnson

Perhaps I missed it, but I could not see Andi’s name as author in this post. One could get the impression that Anthony was the author, if one didn’t go to the link.

biff33

Byline?

MJW

To be pedantic, pterosaurs weren’t actually dinosaurs.

Ceri Phipps

Presumably a denser atmosphere would have more energy intense winds and consequently produce more wind borne dust. This in turn should produce large deposits of loam especially in comparison to modern times. I am not aware of anything in the geological record that indicates this.

Fascinating article – just wanted to say, though, that “mega flora” in your 2nd to last para should be “mega fauna”.

Julian Braggins

Even if animals could exist at that concentration of CO2 it would not explain how the large terrestrial dinosaurs could walk on land, and there are fossil tracks that support this.
Lowered gravity would explain both especially with a denser atmosphere, but in searching threads on this for years have not come up with a satisfactory answer, other than ‘forbidden’ answers that deal with close association with other planets,( V anybody?)

Manuel

· Is our atmosphere being sucked out in to space?
I guess so. I am a mathematician, but from my physics days I remember being shocked by that. I have found the reference in Volume 5 (Statistical Physics), §38, of the monumental Physics Course by Landau and Lifshitz.
The idea is: the distribution of molecules in a classical gas is given by Boltzmann’s Formula:
n = n_0 · exp ( -U / kT)
where n is the distribution of molecules, U the classical potential affecting the gas, n_0 the molecular density when U = 0, T the temperature, and k Boltzmann’s constant.
So for example, since the gravitational potential near Earth’s surface is U = mgh, we have:
n = n_0 · exp (-mgz / kT)
So, as is well-known, the density of the atmosphere decays exponentially when you go up, for low altitudes.
If the altitude variation is bigger, the full Newtonian potential U = GMm / r^2 must be taken, but since U tends to zero when r tends to infinity, we have that exp(-U/kT) does not vanish at infinity.
Therefore Boltzmann’s formula predicts that the state of equilibrium for a gas under Newton’s gravity is to expand with nonvanishing density to the whole space.
Of course, Earth’s atmosphere is far from equilibrium, and the relaxation time for such a big system must be astronomical. Even so, physics certainly hint at a constant loss of gas to space.
Sorry if this was too long, or my English too limited. I am not a professional physicist, by the way. But Landau is was an eminence.
Manuel.

Well, that certainly explains why trilobites were flat, right?
Ummmmm — what?

Jonathan Smith

The first line of enquiry should be to establish the veracity of the atmospheric pressure graph. In the cAGW debate it has been questioned as to whether an average global temperature has any meaning and how do you actually measure such a thing. Could not the same charge be levelled at average atmospheric pressure (how many measuring stations, location etc).
Still, an interesting topic nonetheless. I do enjoy the variety you get on this site, keep up the good work Mr Watts.

Andy Smith

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. Looking at reconstructions of what pterosaurs looked like it seems obvious that one must define their flight rather like Buzz Lightyear’s ie “falling with style”. Their wings are far too rudimentary to take off and fly like a modern bird, rather, I think they must have chucked themselves off of cliffs and ridge-soared or maybe soared the thermals which in mountainous areas are frequently well over 10knots up which should be more than enough for a pterosaur to climb.
It is rumored that a Boeing 747 was soared the length of the New Zealand Southern Alps in wave. So there is loads of energy up there to exploit if you know how.

agwnot

My first reaction was the ideal gas law: PV=nRT, and if the atmospheric temperature increases as most believe has occurred over the last 90 years, then value for PV must increase. Yet, NOAA pressure data shows just the opposite, i.e., P decreasing. Consequently, the slight increase in temperature can not explain the small pressure decrease.
However, I don’t think you can rule out atmospheric warming just yet. As an example, a lower pressure could be explained (as you imply in the post) by a composition change. From Engineering Tool Box; “When water vapor content increases in the moist air the amount of Oxygen and Nitrogen decreases per unit volume and the density decreases because the mass is decreasing.”
Revisiting ideal gas law, and re-writing it to include gas species density, from Wiki we have:
P = p (R/M)T
where;
p = m/V; density
M = molar mass in grams/mole
So if density (p) of the gas mixture decreases due to higher concentration of water, then pressure would decrease proportionally. Remember, moist air is less dense than dry air.
Maybe someone can model this pressure as a function of known or averaged water vapor concentrations as a function of time and then compare to the NOAA pressure chart.

Max

Many of the large dinosaurs could not have walked the earth unless the gravitational force was much lower than it it today. Their bodies would have simply crumpled. Plants were larger also. Why gravity was less beats me. How it effects the atmosphere also. But with less gravity these birds could well have flown.

Raveninghorde

http://www.abc.net.au/science/articles/2012/03/29/3464923.htm
Suggests pressure double about 2.5 billion years ago.

Anopheles

You seem to be describing an atmoshere in which bricks would float. Is there any paleo record which might point to density or pressure, or are we confined to inferences from carbon fixing?

Keith Gordon

What a fascinating article, the reason why myself and many others visit your site continually. I can hardly wait for the next article. I would like some comment if possible, in part 2 on the Pressure/Temperature theory that has been discussed recently, If pressure was higher way back, then it should also have been warmer, according to the theory. I look forward to see if your article and future comments has any support for this controversial theory.
Best regards
Keith Gordon

Matt

When they’ll find penguin fossils in 50 million years from now, scientists will conclude that the atmosphere must have been 2500 denser in our days 😉

tchannon

Who wrote the article because I take it to be someone other than AW?

Kev-in-Uk

I would have thought that water and CO2 was the ‘key’ to all this – given that we have a flipping lot of it! but of course if the atmosphere had bucketloads more atmospheric CO2 (before deposition via carbon based lifeforms?), it would have meant higher density and surface pressures.
The thing is that everything changes at higher pressures – at 4 to 5 bar, the boiling point of water is around 150degC, so presumably evaporation would be less (assuming similar to current atmospheric temps) and air density with less water vapour would be higher? but that would mean less clouds = lower albedo = higher surface temps,etc, etc…
Hmm…seems like a lot to speculate on……!!

Odin's Raven

Some people have suggested that gravity was less, as the big dinosaurs would not have been able to stand with today’s gravity. Presumably that would also have made flight easier.

Simon Barnett

Has anyone compared this to the sea level record to check for inverse proportianality??? Could this offer a better explaination of observed sea level rise than the “evil capitolist polluter” explaination offered by the Malthusians?

Roger Carr

Fascinating (yet again), Anthony.
     And please don’t forget to subtract all the air held under pressure worldwide in vehicle tubes and tyres (tires); sporting balls; and myriad other balloons and bladders.

Stephen Skinner

Great article. Looking forward to part II
Some questions re atmospheric pressure. Surely it is the amount of atmosphere and the mass of the planet that determines what the atmospheric pressure more than it’s composition? As Venus has an atmosphere that is mostly CO2 which has a specific gravity of 1.5 does that explain why the pressure is nearly 100 times that of earth? I put this question to a Nasa expert in response to an article suggestion that the high temperature on Venus was CO2 driven, but his response was they didn’t know why the pressure was so high. From what I can find the depths of atmosphere are: Venus = 250km; Earth = 100km.
Slightly off to one side: What I remember from physics was temperature went up with pressure in a fixed volume. Planetary atmospheres are not confined and on Earth we have extremely hot and cold weather with high pressure systems. I understand high pressures are where the air builds up (gets deeper/higher) and lows where it’s drawn out, both by either a slowing or speeding up jet stream respectively. Therefore atmospheric temperature may be more to do with the speed with which surface temperature is removed, high pressures being slower than low pressures.
Off a bit more to one side: What if the extremely dense atmosphere on Venus was acting like a giant Newton’s cradle and transferring heat right around the planet?

Almah Geddon

Earth and Venus are twins, with the exception of the moon. They probably started out with roughly the same composition, with about the same amount of CO2 and water. This makes sense as they formed in the same part of the original solar dust cloud. So, to distill your musings above : Earth with the creation of the Moon gave us Plate Tectonics, this combined with the distance from the Sun allowed the retention of water, which in turn lead to the carbonate cycle. Venus however never had plate tectonics, which combined its proximity to the Sun lead to disassociation of water, which has lead it to have a 90bar CO2 atmosphere. Life then also turned up on Earth. Life is also very efficient at removing CO2 from the atmosphere.
If a Mars sized impactor not hit the Earth in the Early Heavy Bombardment, we would have had a smaller Earth with no plate tectonics and an atmosphere like Venus’s. There would also be another Mars out there somewhere.
It is somewhat amusing to contemplate that given the CAGW view that humans are destroying the planet by burning fossil fuels, we in fact are most likely extending the habitiability of the Earth by many millions of years by injecting CO2 back into the atmosphere.

Rob L

Air samples from amber suggest atmospheric composition at 100MY only differ greatly in that there is about 35% 02. Assuming same total N2 would result in about 23% higher air pressure but 2x the partial pressure of oxygen (up to 0.4bar from 0.2bar), helpful for making larger insects.
Nitrogen and Oxygen bleed away into space extremely slowly due to magnetosphere, so the only means for loss of pressure is geosequestration, which seems very unlikely for largely inert nitrogen. I can’t see a mechanism that would allow Levenspiel’s suggestion of much higher pressure to be real. http://levenspiel.com/octave/OL_images/DinosaurW.pdf
That 20% increase in air pressure in a 35% O2 atmosphere is not enough to make it possible for 15m wingspan Quetzelcotalus to take off and fly in no wind, but it adds another 2000m depth to the atmosphere thickness. That thickness at typical lapse rates means about 15-20K average increase in temperature taking global average to 25-30°C as well as greatly increased rates of heat convection from equator to pole (polar regions much warmer, tropics just a little). Convection = wind so maybe reliably much stronger winds helped to get big bird aloft.

Bloke down the pub

Neither survived to compete alongside the pterosaurs however. Many believe the concentrations of O2 dropped too low to allow such mega flora to survive beyond the Permian.
Fauna?

Andy

Pterosaurs are not dinosaurs.

Bloke down the pub

The first thing that made me suspicious of the global warming BS was the knowledge from my geology studies that CO2 levels had been much higher in the past and yet the Earth hadn’t gone to hell in a handcart.

John Niclasen

Quite interesting! Some comments:
Life may be the direct cause, why we have continents and therefore plate tectonics. Cyano bacteria produced the oxygen needed to oxidate the rocks into lighter forms, that make up the continents. See:
http://en.wikipedia.org/wiki/Talk%3APlate_tectonics%2FArchive_1#Minik_T._Rosing
I support the idea, that the atmosphere was more dense in ealier times. Our neighbor planets, Venus and Mars, have more than 95% CO2 in their atmospheres, and they don’t have life as we have on Earth. The Earth would most likely have a dense atmosphere with much CO2, if we didn’t have life.
Gravity is hard to grasp completely. The equivalence principle tells us, that gravity locally is the same as constant acceleration. But higher in the atmosphere, the gravity is less than at the surface, which correspond to less acceleration. So what if the atmosphere is constant in weight over time (a short time like 100 years), but it take up more space? Then more of the atmosphere would be higher above the ground, where the gravity is smaller. Would that mean less pressure at the surface? (The atmosphere could take up more space by thermal expansion, if it’s hotter.)

mfo

I don’t know much about pterasaurs but I recall they had hollow bones and were up to the size of a modern day glider.
There is an idea which I’m sure you’ve encountered about a reduced gravity earth in the past:

JuergenK

Time in mya before today / O2 ratio in %
130 / 28; 115 / 29; 95 / 35; 88 / 33; 75 / 35; 70 / 35; 68 / 35; 65,2 / 31; 65 / 29;today / 21
according to Robert Sloan,
http://www.geo.umn.edu/people/profs/SLOAN.html

Tenuk

The atmosphere is not a static system and pressure is constantly varying at any particular place over any period of time due to temperature changes, wind speed changes, topography, particulates and, importantly, how much is being lost to space versus being generated from the crust (e.g. volcanic/tectonic activity). Trying to find an average for such a complex dynamic system is difficult – trying to find a trend from this non-linear average is meaningless.
There also seems to be much confusion about atmospheric dynamics amongst mainstream scientists, who often confuse atmospheric pressure and weight, which are two different things. The atmosphere is a gas and you do not weigh a gas by measuring its pressure. Pressure is a vector in all directions, but (because of gravity), weight is a vector in one direction only, down. The atmosphere does have mass, but weighs nothing. To get a good estimate of the total weigh the atmosphere you would need to freeze a column of air stretching from the ground to the top of the thermosphere of one square meter in cross section and multiply the weight of this by the surface area of the planet, Counting molecules of all the different types of gas making up the atmosphere and adding their molecular weight could also work.

Roy

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 !!
Look on the bright side. There is absolutely no need to worry about the Earth becoming like Mars in 100,000 years’ time. Don’t you realise that global warming will finish us all off long before then?

Interesting. I agree that if these dinosaurs did fly, rather than glide down slope in mountainous areas, the air pressure/density would have to be higher. It was also warmer back then and, no not GHG’s, but an increased air density will increase temperature due to adiabatic compression due to gravity. Back in the Carboniferous there were very large insects which leads to the conclusion that the O2 levels were higher and air denser again leading to higher temperatures which also helps with insect metabolism.
It seems that you are on the right track.

Blokedownthepub claims that past CO2 levels were higher than today. Correct! The Ordovician had levels up around 8000ppmv and suffered a severe ice age.

beng

Some study I read recently suggested that when atmospheric pressure reaches some critical value (above modern values), the Hadley-cell pattern changes dramatically to a “single cell” configuration in each hemisphere, something like Venus. This is a more efficient thermal transport configuration, and is the reason polar temps were temperate-like in ancient times as opposed to today’s arctic temps.