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  1. 15 May '16 09:20 / 1 edit
    http://phys.org/news/2016-05-early-earth-air-today-atmosphere.html

    I find it just a bit surprising that they could actually estimate that from the rocks.
  2. Standard member sonhouse
    Fast and Curious
    15 May '16 14:55
    Originally posted by humy
    http://phys.org/news/2016-05-early-earth-air-today-atmosphere.html

    I find it just a bit surprising that they could actually estimate that from the rocks.
    I would assume it would have to be independently verified, vetted and such. The question then would become how did Earth double that pressure in the last couple billion years.
  3. 15 May '16 17:57
    It is based on evidence that the lava entered sea water. There are salty lakes at high altitudes, so I think it needs to be confirmed with more locations before considering it proven.

    The atmosphere has changed considerably with the great oxygenation with the arrival of plants being one of the best known. It is not surprising that the pressure would change. A more interesting question is what keeps it in balance today?
  4. 15 May '16 20:39
    Originally posted by twhitehead
    It is based on evidence that the lava entered sea water. There are salty lakes at high altitudes, so I think it needs to be confirmed with more locations before considering it proven.

    The atmosphere has changed considerably with the great oxygenation with the arrival of plants being one of the best known. It is not surprising that the pressure would change. A more interesting question is what keeps it in balance today?
    From a probability standpoint it is overwhelmingly more likely that if lava flows into salty
    water it will be into the sea at or near sea level. So while further confirmation would obviously
    be nice [as ever] I wouldn't have this high on my list of possible error factors. And it might
    be possible to tell the difference between a salty lake and sea water [likely different compositions]
    from their effects on the lava.

    One thought I had was in wondering what the tides were like back then, when the moon initially
    formed it was so close that it could well have raised mile high tides every few hours.

    But the paper I found placed the moon at about ~57 Earth radii ~2.5 Ga ago, which is ~80% the
    current separation which leads to about a 30% stronger pull... not enough to raise tides significant
    enough to effect this result. And I don't think that the +~0.2 Ga time difference would affect that
    significantly.
  5. 15 May '16 21:13
    Originally posted by googlefudge
    From a probability standpoint it is overwhelmingly more likely that if lava flows into salty
    water it will be into the sea at or near sea level.
    I disagree. Most major mountain ranges in the world have salt lakes or former salt lakes (salt flats). They are considerably more common than you appear to realise.
    What the continents were like at the time being discussed, I do not know. Do you?
  6. 15 May '16 23:35
    Originally posted by twhitehead
    I disagree. Most major mountain ranges in the world have salt lakes or former salt lakes (salt flats). They are considerably more common than you appear to realise.
    What the continents were like at the time being discussed, I do not know. Do you?
    We are doing a differential here between shorelines of salt lakes and shorelines of the
    worlds oceans...

    I don't care how many salt lakes there are... Sea front is going to massively dominate.

    https://en.wikipedia.org/wiki/Kenorland

    According to the great oracle Wikipedia around 2.7 Ga ago we had a supercontinent named
    Kenorland at that time, and while that would have reduced the coastline some, it's still going
    to dominate over salt lakes. Particularly as a lot of rainfall over land is caused by plant life
    [specifically trees] which pump large amounts of water into the air... and there was no land
    plant life back then. Also supercontinents tend towards having large dessert interiors because
    they are so far from the sea that they don't get rain.

    All factors that make me fairly confident that probabilistically speaking lava flows hitting salt water
    are much more likely to be hitting sea rather than land.

    I'm by no means saying it's impossible [without knowing if they can rule such things out by studying
    the rock formations for chemical signatures to differentiate sea salt water from salt lake water] but
    it's got to be much less likely just given the sheer difference in scale between sea front and lake front.
  7. 16 May '16 06:08
    Originally posted by googlefudge
    We are doing a differential here between shorelines of salt lakes and shorelines of the
    worlds oceans...

    I don't care how many salt lakes there are... Sea front is going to massively dominate.
    I disagree. And certainly not on such a scale that the possibility that it was a salt lake can be ignored.

    it's still going to dominate over salt lakes.
    Ten to one? Hundred to one?

    Particularly as a lot of rainfall over land is caused by plant life [specifically trees] which pump large amounts of water into the air... and there was no land plant life back then.

    Also supercontinents tend towards having large dessert interiors because
    they are so far from the sea that they don't get rain.

    This all might favour salt lakes. Most salt lakes seem to be in low rainfall areas.
  8. 16 May '16 19:30
    Originally posted by twhitehead

    it's still going to dominate over salt lakes.
    Ten to one? Hundred to one?
    [/b]
    I would imagine more like ~10,000 to one or more judging from the map of modern Earth and extrapolating a very rough bold-figure estimate from that.
  9. 16 May '16 19:58
    Originally posted by humy
    I would imagine more like ~10,000 to one or more judging from the map of modern Earth and extrapolating a very rough bold-figure estimate from that.
    https://en.wikipedia.org/wiki/List_of_countries_by_length_of_coastline
    Ignoring for now the coastline length paradox, the whole world has something like 1.1 to 1.6 million kilometres of coastline. Great Salt Lake, Utah, is over 100 kilometres long with a very irregular coast, but lets assume it was dead straight, that is already 200 kilometres of coastline. That's already better than 10,000 to one with just one lake.
  10. 16 May '16 20:06
    If the earth were a single continent then it would have considerably less coast line.

    The Caspian sea is over 1000 km long and below sea level.
  11. 17 May '16 00:20
    Originally posted by twhitehead
    I disagree. And certainly not on such a scale that the possibility that it was a salt lake can be ignored.

    [b]it's still going to dominate over salt lakes.

    Ten to one? Hundred to one?

    Particularly as a lot of rainfall over land is caused by plant life [specifically trees] which pump large amounts of water into the air... and there was no lan ...[text shortened]... t rain.
    This all might favour salt lakes. Most salt lakes seem to be in low rainfall areas.[/b]
    I was wrong, looking over the data I could find, papers on the topic, the figures for
    lake shoreline length significantly exceed coastline length.

    And while I can't find figures specific to salt lakes as opposed to fresh water lakes
    the numbers I found on salt lake volume puts them around 40% total, and as they
    tend to be shallower than non-salty lakes they are likely to at least match fresh
    water lakes in shoreline.

    I still don't know if the study in the OP would be able to differentiate and so they know
    it was sea water and not salt lake water, and I'm still not sure that high altitude salt
    lakes near volcanoes/lava flows is a common enough occurrence to be a likely flaw in the
    study [barring in mind you need to be very high altitude to get a 50% drop in pressure].

    Nevertheless, I was wrong to dismiss this as a factor, lake coverage is much more significant
    than I believed.
  12. 17 May '16 06:19 / 3 edits
    Originally posted by twhitehead
    https://en.wikipedia.org/wiki/List_of_countries_by_length_of_coastline
    Ignoring for now the coastline length paradox, the whole world has something like 1.1 to 1.6 million kilometres of coastline. Great Salt Lake, Utah, is over 100 kilometres long with a very irregular coast, but lets assume it was dead straight, that is already 200 kilometres of coastline. That's already better than 10,000 to one with just one lake.
    I did not know that.

    They estimated that the atmospheric pressure when the lava cooled was ~0.5 atm thus, if it cooled in a salt water lake and if, say, the pressure at sea level was actually ~2 atm back then, the salt water lake would presumably had to be at an unrealistic high altitude and higher than mount Everest.
    Thinking this way makes me think even if it was a salt water lake their estimate couldn't be too far out because, how many salt water lakes do you know of that are at extremely high or low altitude so to massively effect their estimate of atmospheric pressure if the rock was cooled in a lake of equal altitude?
    -those are the only ones that count given the high error of measurement.
  13. 17 May '16 06:31 / 3 edits
    Originally posted by twhitehead
    If the earth were a single continent then it would have considerably less coast line.

    The Caspian sea is over 1000 km long and below sea level.
    If the rock they tested was cooled in a lake below sea level then their estimate of atmospheric pressure at sea level may be slightly too low and it may have been actually slightly below 0.5 atm at sea level. But, given the very high error of measurement, I assume such a lake would be unlikely to have been so below sea level as to massively effect their measurement.
  14. 17 May '16 06:42 / 4 edits
    If the rock cooled in a salt water lake, for their estimate of atms at sea level to be 'wrong' given their high error of measurement, the salt water lake would have to have been at very high altitude. If it was close to sea level, then their estimate will still be about right despite their false premise.

    How many very high altitude salt water lakes have lava flowing into them?
    -Compare that with the number of places where lava flows into the sea.
    What is the ratio of volume of lava flowing into vary high altitude salt water lake to volume of lava flowing into sea?
    I think THAT is a more critical number than the length of coastlines.
  15. 17 May '16 07:47
    Originally posted by humy
    They estimated that the atmospheric pressure when the lava cooled was ~0.5 atm thus, if it cooled in a salt water lake and if, say, the pressure at sea level was actually ~2 atm back then, the salt water lake would presumably had to be at an unrealistic high altitude and higher than mount Everest.
    Thinking this way makes me think even if it was a salt water la ...[text shortened]... ffect their estimate of atmospheric pressure if the rock was cooled in a lake of equal altitude?
    Then why did they take the trouble to search for lava that was supposedly 'at sea level'? If you are right about Mt Everest, then they could simply test all lava finds and if most of them are below 1 atms they can be pretty sure the atmospheric pressure was lower than it is today.