Early Earth’s air weighed less than half of today’s atmosphere

Posted: May 10, 2016 by oldbrew in research, solar system dynamics
Tags: ,

credit: cgtrader

credit: cgtrader


This will have theorists scratching their heads.

The idea that the young Earth had a thicker atmosphere turns out to be wrong. New research from the University of Washington uses bubbles trapped in 2.7 billion-year-old rocks to show that air at that time exerted at most half the pressure of today’s atmosphere.

The results, published online May 9 in Nature Geoscience, reverse the commonly accepted idea that the early Earth had a thicker atmosphere to compensate for weaker sunlight.

The finding also has implications for which gases were in that atmosphere, and how biology and climate worked on the early planet.

“For the longest time, people have been thinking the atmospheric pressure might have been higher back then, because the sun was fainter,” said lead author Sanjoy Som, who did the work as part of his UW doctorate in Earth and space sciences. “Our result is the opposite of what we were expecting.”

The idea of using bubbles trapped in cooling lava as a “paleobarometer” to determine the weight of air in our planet’s youth occurred decades ago to co-author Roger Buick, a UW professor of Earth and space sciences. Others had used the technique to measure the elevation of lavas a few million years old. To flip the idea and measure air pressure farther back in time, researchers needed a site where truly ancient lava had indisputably formed at sea level.

Their field site in Western Australia was discovered by co-author Tim Blake of the University of Western Australia. There, the Beasley River has exposed 2.7 billion-year-old basalt lava. The lowest lava flow has “lava toes” that burrow into glassy shards, proving that molten lava plunged into seawater. The team drilled into the overlying lava flows to examine the size of the bubbles.

A stream of molten rock quickly cools from top and bottom, and bubbles trapped at the bottom are smaller than those at the top. The size difference records the air pressure pushing down on the lava as it cooled, 2.7 billion years ago.

Rough measurements in the field suggested a surprisingly lightweight atmosphere. More rigorous x-ray scans from several lava flows confirmed the result: The bubbles indicate that the atmospheric pressure at that time was less than half of today’s.

Earth 2.7 billion years ago was home only to single-celled microbes, sunlight was about one-fifth weaker, and the atmosphere contained no oxygen. But this finding points to conditions being even more otherworldly than previously thought. A lighter atmosphere could affect wind strength and other climate patterns, and would even alter the boiling point of liquids.

“We’re still coming to grips with the magnitude of this,” [one researcher] said. “It’s going to take us a while to digest all the possible consequences.”

Full phys.org report: Early Earth’s air weighed less than half of today’s atmosphere

Comments
  1. tallbloke says:

    More datapoints needed. This lava flow could have formed during a period when nitrogen fixing bacteria were rampant, but there could have been a sharp turnaround later. Interesting technique though.

  2. Stephen Richards says:

    I’m sorry, but this idea of using bubble trapped air to analyse past atmosphere is almost certainly crap. Molecules move in way as yet uncertain. It has been noted some 40yrs ago that tunnelling can occur where molecules have been trapped. This effect has not been well studied because it is unimportant in the scheme of things.
    I think that their measurements could be showing the effects of molecular tunnelling.

  3. tallbloke says:

    It’s not the pressure of the bubble trapped air they are measuring, it’s the physical size of the bubble frozen into the cooled lava.

  4. oldbrew says:

    The headline should end with: ‘researchers say’ or ‘study suggests’.

  5. Bloke down the pub says:

    With lower atmospheric pressure, and hence a lower boiling point of water, it seems we are luckier than we thought that we still have a watery world.

  6. oldbrew says:

    Bloke: the sun was about 30% dimmer in the distant past. Greenhouse gas theorists claim the Earth should have frozen but didn’t due to the composition of the atmosphere.
    http://phys.org/news/2012-03-fossil-raindrop-imply-greenhouse-gases.html

  7. Perhaps Shaviv’s or Rosing et al.’s theories may be correct, instead of a lot of GHGs, to explain the ice-free earth.

  8. A C Osborn says:

    So now they need to come up with a theory of how Dinasours (pterodactyls) could fly, because it was always assumed that they needed a thicker atmosphere to be able to do so.

    How they think cooling lava bubbles represent the air density I am not, isn’t the air superheated?

  9. gymnosperm says:

    Want to point out that we banter the young dim “sum” with great certainty, even though we have no direct evidence. It is conjecture based on the apparent status of our sun as a main sequence star.

  10. Adam Gallon says:

    AC, no, they don’t.
    These lava flows are dated from 2.7 billion year ago. Pterodactyls didn’t appear until 228 million years ago. Oh, they’re also reptiles, not dinosaurs.
    I’m highly sceptical about using this as a method of estimating atmospheric pressure.

  11. oldbrew says:

    Geological history of oxygen – From Wikipedia

    Stage 1 (3.85–2.45 Ga): Practically no O2 in the atmosphere.
    http://en.wikipedia.org/wiki/Geological_history_of_oxygen

    That covers 2.7 billion years ago [as the report says].

    Timeline of the evolutionary history of life
    http://en.wikipedia.org/wiki/Timeline_of_the_evolutionary_history_of_life

  12. Crosspatch says:

    Assumes ocean quenching. Could have been a lake at altitude for all we know.

  13. Graeme No.3 says:

    Crosspatch:
    The land there is quite ancient, although some argument about its age (one source 2145-2215 Ma, another 2445 -2629 Ma) and it is noted that the volcanic rocks deposited are “only” 10km. thick. They were laid down before the huge deposition of iron oxide thought to have been triggered by the evolution of algae.

    The argument about pterosaurs is clouded by the continuous re-evaluation of their flying abilities.
    The original claim was they couldn’t take to the air at all. This was modified to them being able to glide only. Then they weren’t supposed to be able to take off but hang by their feet from trees or cliffs. When the pteranodon was found with 6 metre wing span this was proof that it must have lived on the ground until someone built a model and showed it could glide, but it was confidently asserted that nothing larger was possible. So when Quetzalcoatlus turned up with a 12 metre wing span things had to change again.
    In the meantime they found track of pterosaurs proving that they could walk on all fours, and studies of the wing structure showed it was capable of flapping. Then computer modelling of the arms revealed that these animals were capable of ‘catapulting’ themselves into the air. A model of a smaller Quetzalcoatlus flew with the aid of a computer and small motors, although mostly gliding but flapping for direction change etc. That this would require endurance impossible in a cold blooded creature was then contradicted by the discovery of some specimens with fur – indicating they were warm blooded. The other problem is the estimation of their weight, Quetzalcoatlus has been put at from 75 to 250 kilograms, with 75-125 more likely for flight.

    So the air 240 – 65 mya didn’t have to be thicker, but some new discovery may upset current thinking.

  14. hunter says:

    Hmmm, we have problems with proxy tree rings that are not even fossilized. Now we are going to have proxies from bazillions of years back based on bubble size to serve as proxy for air density….. What could go wrong with that?

  15. p.g.sharrow says:

    ‘The layers on this 2.7 billion-year-old rock, a stromatolite from Western Australia, show evidence of single-celled, photosynthetic life on the shore of a large lake.” The new result suggests that this microbial life thrived despite a thin atmosphere. Credit: Roger Buick/University of Washington

    Large Lake? not necessarily sea level. The logic here is a bit thin.

    I think I will reserve some disbelief here…pg

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