3
$\begingroup$

In many introductory geology courses, a great deal of time is spent on the historical composition of earth's atmosphere: the great oxygenation event, oxygen maximum during the carboniferous, ups and downs for the CO2 trend...

The graphs supporting those discussions always (according to my memory) show the fractional composition of the atmosphere. But given that for many of the phenomena one wants to explain with this composition trend it would rather be the partial pressures or total mass of each of the composing gases that would be relevant, my question is whether there is (in the scientific literature) an account of the total pressure and / or the total mass of earth's atmosphere on geological time scales?

$\endgroup$

1 Answer 1

3
$\begingroup$

There are few studies of paleobarometry, but to my knowledge at least three different proxies have been used to infer past atmospheric pressures, and they pretty much agree:

  • Fossil raindrop imprints. Som et al. (2012) used such imprints found in tuffs of the Ventersdorp Supergroup (South Africa), dated around 2.7 Ga, to determine the terminal velocity of raindrops and, finally, surface air density. They estimate that it was, at that time, less than twice modern levels (2.3 kg m−3 compared 1.2 kg m−3).
  • $\ce{N2}/\ce{^36Ar}$ ratio. Marty et al. (2013) used fluid inclusions trapped in three different Archean hydrothermal quartz samples to determine the past partial pressure of nitrogen and carbon dioxide, finding $P_{\ce{N2}} \leq 1.1$ bar and $P_{\ce{CO2}} \leq 0.7$ bar.
  • Lava flow vesicle size. Som et al. (2016) used this proxy in a basaltic lava flow from the Pilbara Craton (Australia), emplaced around 2.7 Ga, finding that the late Archaean atmospheric pressure was likely less than 0.5 bar.

But these are only a few data points giving a snapshot of a particular moment in time. I'm not aware that there has been efforts to reconstruct a more comprehensive paleobarometric record.

$\endgroup$
2
  • $\begingroup$ Thx! The wikipedia-page "paleo-atmosphere" to me suggests the empirical methods to determine abundance of atmospheric oxygen and carbon-dioxide should give estimates of their part. pressures (that would be sufficient to discuss most of the remarkable phenomena). So a sober scientific approach would have been to use graphs of these part. pressures. To go to fractional atm. comp., one needs additional info on nitrogen, argon, methane... and this would seem somewhat unnecessary (although the matter seems to be relevant to address the faint young sun paradox, suitable boiling point for water) $\endgroup$
    – 5th decile
    Mar 4 at 16:23
  • $\begingroup$ Ok, in my previous comment (and in my original question) I'm sloppily conflating partial pressure, partial number density, partial mass density... I'm obviously aware that the temperature mediates between them and that paleo-temperature is not constant and an interesting subject in itself. $\endgroup$
    – 5th decile
    Mar 4 at 16:33

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.