Re: Snowball earth, when and why it happened.
- From: zubenelgenubi <zubenelgenubi@xxxxxxxxxx>
- Date: 31 May 2007 05:16:37 -0700
On 31 mai, 09:20, Jake <jcbepst...@xxxxxxxxxxx> wrote:
Snowball earth, when and why it happened.
This is well covered in a wikipedia article
http://en.wikipedia.org/wiki/Snowball_Earth
The first warning is the proposal of a snowball earth is a hypothesis
with considerable supporting evidence but still being worked on.
There is geological period called the Cryogenian Period which
means a cold period, 850 to 630 million years ago. Weathering
is proposed to have removed move of the CO2 from the atmosphere
leading to a runaway drop in temperature, the increased ice
coverage causeing less and less absorption of light from
the sun.
The CO2 can eventually return to the atmosphere via volanic
action in which the prior form limestone descends to such
depths that it is termally decomposed to give CO2. So that
represents a CO2 cycle. This process especially occurs with the
collision of plates.
From the wikipedia article---
"The carbon dioxide levels necessary to unfreeze the Earth have been
estimated as being 350 times what they are today, about 13% of the
atmosphere.[12] Since the Earth was almost completely covered with
ice, carbon dioxide could not be withdrawn from the atmosphere by the
weathering of siliceous rocks. Over 4-30 million years, enough CO2 and
methane, mainly emitted by volcanoes, would accumulate to finally
cause enough greenhouse effect to make surface ice melt in the tropics
until a band of ice-free land and water developed;[13] this would be
darker than the ice, and thus absorb more energy from the sun -
initiating a "positive feedback".
On the continents, the melting of glaciers would release massive
amounts of glacial deposit, which would erode and weather. The
resulting sediments supplied to the ocean would be high in nutrients
such as phosphorous, which combined with the abundance of CO2 would
trigger a cyanobacterial population explosion, which would cause a
relatively rapid reoxygenation of the atmosphere, which may have
contributed to the rise of the Ediacaran biota and the subsequent
Cambrian Explosion - a higher oxygen concentration allowing large
multicellular lifeforms to develop. This positive feedback loop would
melt the ice in geological short order, perhaps less than 1000 years;
replenishment of atmospheric oxygen and depletion of the CO2 levels
would take further millennia.
It is possible that carbon dioxide levels fell enough for Earth to
freeze again; this cycle may have repeated until the continents had
drifted to more polar latitudes.[14]
*****
None of this means anything. There is no conclusive proof that
mankind's activities have anything to do with global warming if in
fact it exists. You're a senile old fool exleth, now do us a favor and
get lost!
.
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