Hi, Bob, List,
For further references that illuminate the
origins of this theory, I suggest you glance
at a copy of Classic Illustrated Comic Number
149 -- "Off On A Comet" by Jules Verne,
which explicates the theory in greater
technical detail.
For researchers willing to tackle the source
materials without the comic book pictures:
http://www.gutenberg.org/etext/1353
Myself, I like the comic book version better.
Sterling K. Webb
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----- Original Message -----
From: "Robert Verish" <[email protected]>
To: "Meteorite-list Meteoritecentral"
<[email protected]>
Sent: Wednesday, April 07, 2010 9:32 AM
Subject: [meteorite-list] Comets and eskers and drumlins - Oh my!
The following is a review of a bizarre theory that comets are involved
in the formation of eskers and drumlins. -- Bob V.
--------------------------------
Wednesday, April 7, 2010 5:12 AM
From: "Technology Review Feed - arXiv blog" <[email protected]>
the physics arXiv blog
Could A Comet Tail Have Scarred the Earth in the Recent Past?
Posted: 06 Apr 2010 09:10 PM PDT
The idea that the Earth shows signs of having repeatedly passed
through the tail of a comet does not bear up to scrutiny.
One of the puzzles that geologists occasionally ponder is the nature
of eskers and drumlins.
Eskers are winding ridges a few tens of metres high that look
remarkably like railway embankments. Indeed they are often used as
readymade roads and run up and down hills over distances that
sometimes stretch to hundreds kilometres.
Drumlins, on the other hand, are tear drop-shaped hills a few tens of
metres high and a hundreds of metres long. They often appear in large
numbers with the same orientation in drumlin fields .
Geologists have long assumed that eskers and drumlins are formed by
glaciers and left behind after these ice giants retreated.
There are essentially two problems. The first is the internal
structure of these formations. Eskers and drumlins have have an outer
layer of water-borne clay and silt with attendant fossil debris. This
covers an inner core made of unsorted boulders and rocks which are
entirely free of fossils. These inner cores do not appear to have been
affected by the action of water. How does this structure arise?
The second is that if glaciers are responsible for eskers and
drumlins, they ought to be forming now. And yet nobody can find
anywhere on Earth where these structures are currently forming.
Today, Milton Zysman and Frank Wallace publish on the arXiv their
explanation for the formation of these objects and it makes for
fascinating, if not entirely convincing, reading.
Zysman and Wallace say that eskers and drumlins are the debris left on
Earth after our planet repeatedly passed through the tail of a giant
comet. They say this explains the distribution of eskers and drumlins,
which often form in roughly parallel lines.
It also explains their internal structure. The rocky core of these
objects is pure cometry debris which explains the absence of fossils.
The outer layer built up later through the action of water and ice.
The cometary origin, they say, also explains the rather unique shape
of the individual rocks in the cores and the striations that mark them
predominantly in line with their longest axis. (Apparently, these
markings are consistent with the process of erosion that must occur in
comet tails.)
Zysman and Wallace also point out that the ice age that is associated
with esker and drumlin formation must have been caused by the comet
tail, which would have enveloped Earth in a layer of dust that rapidly
cooled the planet.
This is not an entirely new idea. Various commentators have suggested
that many of Earth's rocks and much of its water and atmosphere may
have come from comets. And indeed this paper is an edited version of
one the authors originally gave in 1997.
However, Zysman and Wallace's idea as it stands is little more than an
interesting guess. What of isotopic evidence? Presumably the isotopic
content of the rocky cores should differ in a measurable way from
material on Earth that has other origins. If this work has been done,
they make no mention of it.
And the fact that we have not seen eskers and drumlins forming in the
two hundred years that we've been looking does not mean they did not
form in the past, during the many millennia that glaciers were
ravaging the Earth. (In fact, there are recent reports that scientists
have seen a drumlin forming for the first time in Antarctica.)
And finally, it's hard to imagine that the debris from a comet tail
hitting the atmosphere at several tens of kilometres per second would
then land in a tear drop shape just a few tens of metres in size or
form a line a few tens of metres wide but hundreds of kilometres long.
It should be straightforward to refute or dismiss this idea by
simulating of the kind of debris patterns that this kind of event
would produce. And in any case, the heat generated when rocks enter
the Earth's atmosphere melts their outer surface, giving them a
"fusion crust" that is easy to identify. Why don't the rocks in esker
and drumlin cores have fusion crusts?
Putting Zysman and Wallace aside, however, it is still possible that
the Earth has been shaped by extraterrestrial forces in ways that we
are only beginning to grasp. For example, there is growing evidence
that the Solar System has been regularly disturbed by passing stars
and their accompanying discs of ice and dust. These events must have
had a dramatic impact on our world.
It is becoming increasingly clear that conditions on Earth are a
product of the interplanetary and interstellar environment in ways we
are only beginning to understand. And of course we need new hypotheses
to explore this idea to its fullest extent.
Ref: http://arxiv.org/abs/1004.0416 : Tails of a Recent Comet: The
Role Cometary Jets Play in Crustal Formation Esker/ Drumlin Swarms
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