Comments below:
> [Arlo]
> Chapter One of Columbia's History of the World is a
> good overview of
> the large-scale geologic forces that operate on the
> planet. The
> geologic record indicates that during each "Ice Age"
> (defined as a
> period when the north and south magnetic poles occur
> over land
> masses, allowing for the formation of large polar
> ice caps) there are
> recurring cycles of glaciation, where glaciers
> progress towards the
> equator and then rescind to the caps. The end of the
> actual Ice Age
> occurs when the magnetic poles move over water,
> allowing for the mass
> de-icing of the polar caps. Earth's geologic record
> indicates that
> the "norm" for the planet is the long periods of
> "tropic" conditions,
> as during the Mesozoic Era, that occur when the
> magnetic poles occur
> over water. "Ice Ages", times when the poles occur
> over land (as they
> do now), are period aberrations to the norm.
> From Wikipedia on the glaciation cycle:
> "Within the ice ages (or at least within the last
> one), more
> temperate and more severe periods occur. The colder
> periods are
> called glacial periods, the warmer periods
> interglacials, such as the
> Eemian interglacial era.
> Glacials are characterized by cooler and drier
> climates over most of
> the Earth and large land and sea ice masses
> extending outward from
> the poles. Mountain glaciers in otherwise
> unglaciated areas extend to
> lower elevations due to a lower snow line. Sea
> levels drop due to the
> removal of large volumes of water above sea level in
> the icecaps.
> There is evidence that ocean circulation patterns
> are disrupted by
> glaciations. Since the Earth has significant
> continental glaciation
> in the Arctic and Antarctic, we are currently in a
> glacial minimum of
> a glaciation. Such a period between glacial maxima
> is known as an interglacial.
> The Earth is now in an interglacial period known as
> the Holocene. It
> was conventional wisdom that "the typical
> interglacial period lasts
> about 12,000 years" but now appears to be incorrect
> from the evidence
> of ice core records. Therefore, it has been widely
> contradicted
> recently; for example, an article in Nature[4]
> argues that the
> current interglacial might be most analogous to a
> previous
> interglacial that lasted 28,000 years."
> From Wikipedia on the causes of Ice Ages:
> "The geological record appears to show that ice ages
> start when the
> continents are in positions which block or reduce
> the flow of warm
> water from the equator to the poles and thus allow
> ice sheets to
> form. The ice sheets increase the Earth's
> reflectivity and thus
> reduce the absorption of solar radiation. With less
> radiation
> absorbed the atmosphere cools; the cooling allows
> the ice sheets to
> grow, which further increases reflectivity in a
> positive feedback
> loop. The ice age continues until the reduction in
> weathering causes
> an increase in the greenhouse effect."
> There are, to be fair, other theories as to the
> cause of periodic Ice
> Ages, such as reduced solar activity, the build up
> of greenhouse
> gases, etc, but the coinciding of magnetic poles
> over land masses
> seems to me to be the higher quality explanation
> (keeping in mind
> that the evidence of the Ice Age cycles, or the
> intra-Ice Age
> glaciation cycles, is not in dispute).
> I'm not saying, of course, that you will have to
> begin crafting
> mammoth-hide snow boots, but someday one of your
> great-great....
> grandchildren will. And if mankind weathers out the
> thousand-plus
> years of Hoth (Star Wars geek reference), they have
> a future of
> Dagobah ('nother one for ya) to look forward to.
Ok, this was informative, but I was referring to
the following that you mentioned previously.
> [Arlo]
> We live presently in between two cycles of
> glaciation..."
Firstly, you mention we are in-between two cycles,
how do we know another cycle is coming?
[Arlo]
> Geological records would tell us that before this
> present Ice Age ends, the Earth will see at least
> one more cycle of
> "glacial progress", before the Earth returns to its
> "normal" state...
How do we know "at least one more cycle"? Also,
the timing of this "glacial progress" in which you
state, "before... return(ing) to... 'normal'
state..."? I understand geologic record,
interglacial, glacial, regression, this "normative"
period, etc..., but I do admit I don't know about,
"Hoth... (and) Dagobah"
thanks.
SA
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