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Thread: When was the earth totally ice/snow-free?

  1. #1
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    When was the earth totally ice/snow-free?

    When was the last time that the earth was completely ice-free ie no ice at the poles, zero snow on Kilimanjaro, Alps, Everest etc: thousands, millions or billions of years ago?
    Last edited by wd40; 2020-May-03 at 07:56 AM.

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    Since the Sun has been graduallly increasing in luminosity over time, I doubt very much that the Earth has ever been ice free - not since the end of the last great bombardment, anyway.

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    The Late Heavy Bombardment ended about 3.8 billion years ago. That long ago, the Alps, Himalayas and Kilimanjaro did not yet exist.

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    Paleocene-Eocene period, I believe.

    https://en.wikipedia.org/wiki/Paleoc...hermal_Maximum
    Last edited by Roger E. Moore; 2020-May-03 at 12:53 PM.
    Do good work. —Virgil Ivan "Gus" Grissom

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    When the continents were lumped together as Gondwanaland, the remaining oceans might have been ice free For a long time (although i believe there was an ice age in pangia) for the reason that you need either a land mass like Antarctica or a restricted land passage near the pole to prevent strong tidal mixing of the oceans.
    sicut vis videre esto
    When we realize that patterns don't exist in the universe, they are a template that we hold to the universe to make sense of it, it all makes a lot more sense.
    Originally Posted by Ken G

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    The Eocene is probably the best candidate for a 'recent' ice free period (~50 million years ago). The Eocene optimum and Paleocene–Eocene Thermal Maximum were very warm periods and the polar ice caps were probably not present. They were not permanent features in the Palaeocene (the Antarctic one started forming in the late Eocene, the Greenland one about 20 million years later) and there is no evidence for them in the temperature responses in the Eocene. Trouble is that even in this period I suspect quite strongly (but cannot find references to support) that there were places with an altitude high enough to see permanent snow and ice. The planet was very humid at this point so each 1000m of altitude probably produce only 3-5C or so drop in temperature. It still wouldn't take a particularly tall mountain to see permanent snow.

    So your answer could be millions (Eocene) but more likely to be billions (Hadean), as Eburacum45 says.

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    Quote Originally Posted by Shaula View Post
    So your answer could be millions (Eocene) but more likely to be billions (Hadean), as Eburacum45 says.
    Well, Hadean lavaworld for sure.
    Do good work. —Virgil Ivan "Gus" Grissom

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    A Farewell To Ice by Peter Wadhams of Cambridge University Polar Centre includes a chapter titled A Brief History of Ice on Planet Earth. I just wrote the following summary of this chapter, hopefully not over-simplifying.

    Chapter Three: A Brief History of Ice on Planet Earth

    This chapter provides a superb contextualisation of human history within the deep time horizon provided by geology, over the 4.54 billion years since our planet condensed out of the solar nebula. Earth had no ice at all for several billion years. The surface was at first molten, with almost no oxygen in the atmosphere. Life started up after half a billion years or so, and then photosynthesis began about two billion years ago, gradually starting to inject oxygen into the air.

    One big icy setback was the first known snowball earth, when the temperature of the whole planet fell below freezing and ice covered all the oceans up to a kilometre deep. (Not sure if these glaciers also covered all the land or if some mountains poked through). The Huronian glaciation lasted for a hundred million years until 2.3 billion BC, but somehow microbial life survived this harsh period. The sun was 15% dimmer than today. It seems that a slowing of volcanic activity reduced the greenhouse effect, expanding glaciation until the white surface reflected 80% of the sunlight back to space, generating a completely white planet until volcanoes broke up the ice by sending up warming clouds of methane and CO2.

    The next snowball earth period was 710 million years ago, when all the continents came together to form the single super-continent Pangaea, near the equator, which somehow caused silicate weathering that removed so much CO2 from the air that the planet froze again. The last snowball was 635 million years ago, lasting about ten million years, possibly caused by a cloud of space debris blocking the sun. But the primitive algae survived all this and kept on pumping oxygen into the air, which eventually reached a threshold in 580 MBC whereby single living cells could combine, producing the Cambrian Explosion.

    The relevance for current iciness is the speed in the geological record of changes in CO2 level. We now add about three parts per million of CO2 to the air each year. The fastest geological rate of CO2 increase looks to be about 0.2 ppm after the asteroid wiped out the dinosaurs in 65 MBC. That caused major heating, but nothing compared to what we are now doing.

    For the last 50 million years, ocean sediments show the temperature gradually fell until the ice age temperature oscillations started about 6 million years ago. The interesting thing is that the natural temperature reached a point whereby tiny oscillations of our orbit – the roundness, tilt and wobble – were enough to trigger advance and retreat of glaciers. Previously these orbital factors were swamped by terrestrial effects. The orbital change in incoming sunlight against the seasons was enough to create accelerating feedback loops. CO2 and temperature gradually fell for a hundred thousand years, until suddenly bouncing back to their previous level. So we see the sawtooth graph of CO2 over the last million years producing repeat ice ages until humans came along and stopped them.

    Ruddiman argues that the rise of agriculture in the Neolithic period about ten thousand years ago released so much methane from rice and cows that it disrupted the natural process which would have already had the planet fall back into a new ice age. The situation now is that the great climate disruption we have created with fossil fuels dwarfs anything agriculture could cause, sending us on an iceless hothouse trajectory. The last time the planet had the current CO2 level the sea was about 20 metres higher, so that is the equilibrium that will arise unless we work out a technological fix for climate change.

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    Thanks for that useful summary. In forming a background to current heating trends, it should be more widely known. I do not think any of that history is controversial. Maybe the triggering of ice ages in the last million years, the evolutionary period for humans, is of interest. Clearly the ice free period was a long time ago .
    sicut vis videre esto
    When we realize that patterns don't exist in the universe, they are a template that we hold to the universe to make sense of it, it all makes a lot more sense.
    Originally Posted by Ken G

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