Earth’s Ancient Barometric Pressure

Posted: March 6, 2020 by oldbrew in atmosphere, History, paleo, pressure

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A rare chance to brush up on your *vesicle paleobarometry* — or to put it another way, learn that air pressure at sea level has not always been around the 1 bar (1000 mb) that we expect to find nowadays. According to the ideal gas law, pressure and temperature are closely related, implying historic climate variability, but results so far seem inconclusive.

NASA says:
Researchers supported in part by the NASA Astrobiology Program have attempted to better understand global barometric pressure on Earth during the Archaean by studying vesicle sizes in 2.9 billion year-old lavas that erupted near sea level.

Today, Earth’s global barometric pressure is 1 bar at sea level. However, barometric pressure has changed throughout the planet’s history.

Samples were taken from the Pongola Supergroup from Mahlangatsha and Mooihoek, eSwatini (formerly Swaziland), and the White Mfolozi River gorge of KwaZulu-Natal, South Africa.

This study is only the second time the method has been employed, and the team was unable to gather reliable results due to aspects of the sample site.

The researchers recommend that future studies be undertaken at other locations, and provide guidelines for vesicular paleobarometry based on the outcomes of this project.

The study, “Vesicle paleobarometry in the Pongola Supergroup: A cautionary note and guidelines for future studies,” was published in the journal South African Journal of Geology. The work was supported by NASA Astrobiology through the Exobiology Program.
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Vesicle paleobarometry in the Pongola Supergroup: A cautionary note and guidelines for future studies
E.A. Goosmann ; R. Buick ; D.C. Catling ; C. Luskin ; N. Nhleko
South African Journal of Geology (2020)

From the abstract:
Earth’s global barometric pressure, currently 1 bar at sea level, may have changed over its 4.5-billion-year history. Proxy measurements, including N2/36Ar ratios in ~3.5 to 3.0 Ga hydrothermal quartz, ~2.7 Ga raindrop imprints, and ~2.7 Ga vesicle sizes in subaerial basalt lava flows indicate Archean air pressure could have been between 0.1 and 1.2 bar. However, some models argue air pressure in the Archean should have been much higher than now and could allow pressure broadening of greenhouse gas absorption lines to counteract the “Faint Young Sun”. Thus, additional paleobarometric measurements would be useful to further constrain Earth’s atmospheric evolution.

  1. Curious George says:

    At the first glance, it may be about as reliable as a temperature divined from tree rings. There are just too many variables.

  2. oldbrew says:

    This 2016 research finds atm pressure quite low in the Archaean.

    Earth’s air pressure 2.7 billion years ago constrained to less than half of modern levels

    Then they fall back on greenhouse gas theory, despite all the evidence clearly showing that historical temperature rise preceded rises in carbon dioxide.

  3. gallopingcamel says:

    I don’t buy the low surface pressure argument absent a plausible mechanism for increasing or decreasing the amount of oxygen, nitrogen, carbon dioxide, methane or whatever.

    If the surface atmospheric pressure was less than 0.5 bar 2.7 million years ago the average global temperature would be -18 degrees Centigrade (aka Iceball Earth) whereas according to Robert Rhode, based on geologic evidence the climate was warmer than today: