Snowball Earth

Life goes on.

Given my current interest in ice ages, I naturally took a lot of interest in Youtube’s Snowball Earth, when some 700 million years ago there was ice covering the entire planet. According to Wikipedia:

Global temperature fell so low that the equator was as cold as modern-day Antarctica. This low temperature was maintained by the high albedo of the ice sheets, which reflected most incoming solar energy into space. A lack of heat-retaining clouds, caused by water vapor freezing out of the atmosphere, amplified this effect.

The whole Earth got covered in ice, and stayed encased in ice for some 50 million years. The most interesting thing to me was that, according to the Youtube video, the ice age ended with the eruption of “10,000 volcanoes”.

And this is what I would have expected. For once the entire Earth was covered in kilometres of ice, the surface rocks beneath the ice would have gradually warmed up. The centre of the Earth is currently believed to have a temperature of 7000ºC, and so the Earth’s  mean temperature is maybe 2000ºC, and if no heat could escape through the ice, the Earth would have very gradually acquired that uniform temperature throughout.

And 2000ºC is well above the melting point of granite (about 1200ºC). So the surface rocks beneath the ice would have slowly climbed towards melting point. More or less the entire surface of the Earth beneath the ice would have turned into molten or near-molten rock. So of course there would have been 10,000 volcanoes. And they would have melted the ice pretty rapudly.

The same programme said that in the end-Permian ice age also ended with large scale volcanic eruptions. Volcanic eruptions at the end of ice ages should be expected.

But I think that when the surface of the Earth heats up by several hundred degrees, the surface will expand: most materials expand when heated. And this thermal expansion would have meant that rocks all over the surface of the earth would have been in compression as they pushed against each other, and the compression would have have been stronger the higher the surface rock temperature was. And when rocks become highly compressed at the surface of the Earth, they are likely to buckle or fracture, and the only direction they can buckle is upwards. They’ll form hills and mountains.

I wondered how compressed the rocks would become. The coefficient of linear thermal expansion of sandstone, α, is about 12 x 10-6, such that the length L of a rock is given by

L = Lo.( 1 + α.ΔT )

where Lo is the initial length, and ΔT the increase in temperature. And so if Lwas 1,000 km, and ΔT was 500ºC, the sandstone rocks along the 1,000 km length would have increased in length by 6 km. And if the crust was 1 km thick, a total of 6 cubic km of rock would have to buckle or get squeezed upwards to form a mountain. And given a 30º angle of repose of a pile of broken rock, the resulting mountain would be 1.86 km high.

And these mountains would form along ridges, one range along one expanding axis, another at a right angle to that axis. And in between these upthrust ridges would be unbuckled plains.

And this suggests a variant of plate tectonics, one in which the forces acting to build mountains are the product of thermal expansion of surface rocks rather than the up-welling convection in the Earth’s mantle beneath the plate.

And these mountain ranges would lie roughly along N-S and E-W axes, because the Earth’s poles are cooler than its equatorial regiions, and so there would be a distinct  N-S and E-W symmetry about the system of mountain ranges (the Andes being one  N-S  range of mountains and the Himalayas an E-W range of mountains).

And these expanding and contracting plates would push and pull each other around. During ice ages, the plates would warm up and expand and push against each other, and during interglacial periods when the surface rocks cooled down, they would contract and pull against each other. And this would produce flat plains like the US midwest or the Russian steppes. And if they pulled strongly enough apart, the rigid crust would fracture, and molten rock would well upwards to fill the gap (e.g. the mid-ocean Atlantic ridge).

The forces acting horizontally in these plates would be purely a function of their temperature and their lateral width Lo. Large plates would generate larger forces along their perimeters than small plates. So if the large Pacific plate has volcanic activity all around its perimeter (the “ring of fire”), it’s largely a consequence of its size.

Periods of orogeny (mountain-building) would be largely restricted to the ends of long and deep ice ages when surface rock temperatures had risen to sufficient temperatures for surface rock buckling to commence, and volcanoes to erupt through the broken rock. They would probably have been quite short and sudden. Entire mountain ranges might have been thrown up in days. And then when the compressive stresses had been relieved, very little mountain-building would take place until the end of the next major glaciation.

And life did go on through the Snowball Earth episode. In fact, the end of it brought the appearance of the first multicellular lifeforms. But that’s another story.

About Frank Davis

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10 Responses to Snowball Earth

  1. RdM says:

    Lots of bright minds out there. For instance:
    https://malagabay.wordpress.com/2017/06/29/flipping-geology-forgotten-friction/

    And I’m not sure what to make of this:
    https://malagabay.wordpress.com/2017/05/14/plate-tectonics-versus-earth-expansion-a-gravity-problem-by-louis-hissink/

    I don’t quite agree with Louis Hissink, he doesn’t think gravity extends down to the sub-atomic
    level, as I read him earlier, whereas Miles Mathis does, and shows how it does.
    But still … Plenty of reading… and I respect his geology background and other writings.

    • Frank Davis says:

      “A fundamental tenet of this Ecclesiastical Science stipulates sinful strata is condemned to hell for millions of years before being resurrected as metamorphic rock.”

      :-)

  2. Pete j says:

    Frank, this may be of some interest too.

    • Frank Davis says:

      Yes, I’ve heard the idea that there’s a mantle plume under the Hawaiian islands. And it’s a pretty good explanation for the Hawaiian islands. But I’ve never heard an explanation for mantle plumes. So I think they’ve just kicked the problem downstairs.

      Approaching the problem my way, with rocks under glaciers heating up, and cooling down again when the glaciers melt, and hot rocks being in compression, and cool rocks in tension, I wondered whether the whole very large Pacific plate (which pretty much covers half the Earth) might actually be in tension, and the Hawaiian islands and other islands might appear where the tensed plate has fractured, and molten rock come up through the fracture. But that was just an idea I was toying with.

      • beobrigitte says:

        Yes, I’ve heard the idea that there’s a mantle plume under the Hawaiian islands. And it’s a pretty good explanation for the Hawaiian islands. But I’ve never heard an explanation for mantle plumes. So I think they’ve just kicked the problem downstairs.
        The mantle plume is the explanation for the existence of the Hawaian Islands; it had puzzled me simply because Hawaii is right in the middle of the pacific plate
        https://qph.fs.quoracdn.net/main-qimg-764c8a5f7aabe7f4bea869624d987122
        Your theory:
        I wondered whether the whole very large Pacific plate (which pretty much covers half the Earth) might actually be in tension, and the Hawaiian islands and other islands might appear where the tensed plate has fractured, and molten rock come up through the fracture. But that was just an idea I was toying with. does make sense.
        I have been following the Hawaii eruption for a while; Mt. Kilauea has been erupting since 1983 and despite this there had been a lava lake in the main crater. This has now drained (?into the fissures) presumably below groundwater level and there are steam explosions from the main crater.
        Perhaps the most natural state of our planet is being covered in ice with an occasional accumulation of warmth below the ice sheet causing the melt of it to then cool down again.
        The tectonic plates’ movements + volcanic activity also may well prolong/amplify the warmer periods?
        In any case, we find that nature (a little of it can currently be observed with the naked eye in Hawaii) is far more powerful than mankind, so a “climate change” industry is a waste of money which could be invested into living with our ever changing planet.

  3. Pingback: Marvel Loose Sat-Ear-Day – Library of Libraries

  4. sackersonwp says:

    Could this be a factor in climate change also?

    • Frank Davis says:

      Milankovitch cycles include variations in the ellipticity of the orbit of the Earth. But that is said to happen every 100,000 years. Maybe they’ve found a new cycle to add to the three existing ones? At present, because they all entail quite small variations in the amount of sunlight reaching the Earth, they are not believed to actually cause ice ages and interglacials, but to instead regulate them a little.

  5. Pingback: Hills | Frank Davis

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