Is there any evidence for higher air pressures in the geological past?

Question

I was curious about how the Earth's overall air pressure has varied over time, and tried to take a look around the internet. However, Google pops up a lot of sites with questionable science proposing that the air pressure was much higher in the past. The more outrageous claims (such as those by David Esker) are dealt with on Skeptics.SE.

However, there are more reasonable claims that air pressure was perhaps 4 or 5 times higher in the Mesozoic, thus allowing pterosaurs to fly more effectively, etc. The websites making such claims do heavily set off my pseudoscience alarms, but then some are published by the American Chemical Society by reputable sounding scientists with references to papers.

There is evidence that in the far distant past, air pressures were lower than they are currently. But after the changes to the atmosphere wrought by photosynthetic life, is there any evidence supporting the various theories of higher air pressures?

Answer 1

Yes, there is. But the data is still very sparse and errors are large.

Past atmospherics pressures have been estimated by at least three different methods:

1. Isotopic composition of fluid inclusions trapped hydrothermal quartz ( Nishizawa ey al 2007; Goldblatt et al 2009; Marty et al, 2013)

Image from Fig. 2 of Nishizawa et al 2007.

2. Size distribution of gas bubbles in basaltic lava flows (Som et al 2016)

Figure 3c of Som et al (2016): Beasley River geologic context and flow detail (scale bar, 1 cm)

3. Size distribution of fossilised raindrop imprints (Som et al, 2012; Kavanagh & Goldblat, 2015)

Figure 1 of Som et al (2012) The 2.7-billion-year-old Ventersdorp Supergroup raindrop imprints lithified in tuff at Omdraaivlei, South Africa.

Each study is based on samples that capture the conditions at a fairly specific point in time. Therefore, different results not necessarily contradict each other, but offer a sense of how variable has been the atmospheric pressure over geological time.

The size distribution of fossilised raindrop imprints might have a large range of error due to the many factors that influence drop size beside atmospheric pressure. However, some studies suggest that the Archean (4 to 2.5 billion years ago) atmosphere was almost ten times denser than it is today (Kavanagh & Goldblat, 2015). That figure is based on fossilized raindrop imprints dated about 2.7 billion year ago, that is after the evolution of photosynthesis, but still in its early stages, when most oxygen was absorbed by the oceans and there was very little of it in the atmosphere. On the other hand, studies based in isotopic composition of fluid inclusions and bubbles in basaltic lava have found that the atmosphere was less dense than it is today.

These studies are of great interest, as a denser atmosphere even if poor in greenhouse gasses can produce warmer surface condition, helping to resolve the faint young Sun paradox. In a nutshell, this paradox refers to how could liquid water exist on Earth in the past when the sun was much fainter than it is today.

It is important to note that the additional temperature in a thick atmosphere doesn't come from adiabatic warming as some people have suggested here. A good treatment of the phenomena is presented by Chemke et al (2016) in the paper "The thermodynamic effect of atmospheric mass on early Earth's temperature", there they say:

We find that higher atmospheric mass tends to increase the near-surface temperature mostly due to an increase in the heat capacity of the atmosphere, which decreases the net radiative cooling effect in the lower layers of the atmosphere. Additionally, the vertical advection of heat by eddies decreases with increasing atmospheric mass, resulting in further near-surface warming.

Answer 2

All manner of isotopic analyses confirms that the chemical composition of the earth's atmosphere has fluctuated wildly in the past. Besides the Archean hypoxic atmospheres of 2.5 billion years ago, the late Paleozoic saw oxygen concentrations that were much higher than they are today allowing a wide variety of giant insects to thrive (simple diffusion is a large part of insect respiration). Some believe that in addition to much higher oxygen levels, a much higher air density (pressure) may have accelerated the development of flight in these insects:

ATMOSPHERIC OXYGEN, GIANT PALEOZOIC INSECTS AND THE EVOLUTION OF AERIAL LOCOMOTOR PERFORMANCE

By the way, the internets are full of people who don't understand the difference between "high oxygen partial pressure" and "high atmospheric pressure".

Answer 3

I think there is good evidence that air pressure was 3-5 times higher during hothouse periods like the Mesozoic Era.

It solves how 1 Pterosaurs could fly 2 Sauropods could grow up to 80 metric tons 3 Why arthropods were much larger 4 The climate was so warm and wet, even at the poles.

Someday I plan on getting a team together to investigate this further; not that the atmosphere was denser at the surface, but how it would be possible. The obvious answer will be found in the correlation between ocean chemistry cycles and hothouse/icehouse climate cycles. The correlation suggests that the oceans were significantly warmed via geothermal heat flux but more importantly hydrothermal pumping, causing increased degassing and evaporation, and thus a thicker atmosphere.

The fact that marine chemistry and the major climate cycles correlate very well and marine chemistry is controlled by variable rates in sea floor production suggests some link between the two and it is sad to me that no one has investigated this link beyond invoking that CO2 is the overarching climate control knob, which all evidence suggests to be erroneous. It's basic physics - gravitational potential energy and kinetic theory of gases - the heavier the atmosphere over your head the warmer the surface will be.

http://ftp.earthbyte.org/Resources/Pdf/Muller_etal_2013_Seawater_chemistry_driven_by_Supercontinent_assembly_breakup_dispersal_Geology.pdf

https://s3.amazonaws.com/academia.edu.documents/3468640/Veizer_Nature_2001.pdf?AWSAccessKeyId=AKIAIWOWYYGZ2Y53UL3A&Expires=1534442228&Signature=3Pxz67vBnWWnBbh%2BUzIp%2BwnewP4%3D&response-content-disposition=inline%3B%20filename%3DEvidence_for_decoupling_of_atmospheric_C.pdf

Another good comparison would be crocodilia since they are still extant today. They were much larger in the mesozoic (up to 8 tonnes!) but food availability is not limiting the size of these creatures today. The size limitation is due physical limitations as body mass increases. In a denser atmosphere you explain why these physical limitations are at a much larger body size.