Joel wrote:
<< Paul,
If you could spare a few moments could you give us a few highlights as it
relates to to the following article posted on the AiG website this morning:
"Do Greenland ice cores show over one hundred thousand years of annual
layers?"
http://www.answersingenesis.org/docs2001/0704icecores.asp >>
Oard has added some new arguments to the creationist response to ice cores,
and I want to do some more research before making a final answer; but, I can
make a preliminary answer that will probably stand up.
His statement that all of the methods of dating ice cores are dependent upon
an assumption about the thickness of the annual layers is false. Although
average annual thicknesses are estimated, these are preliminary judgements
which are later corrected if the annual layer count shows otherwise.
The methods measuring hoar frost layers, electrical conductivity, and dust
content are independent of each other and of any assumptions as to the
thickness of the annual layers. In addition they have been shown empirically
to be annual.
His second argument that the climate would have been warmer in the past and
therefore melt layers (not hoar frost layers which he confuses with melt
layers) would have been produced and these melt layers would be counted as
annual layers is a half truth. Warmer weather, i.e, temperatures above
freezing, would have produced melt layers; but, melt layers have a different
structure and appearance than hoar frost layers and though like weeds in a
flower garden are pests, they are relatively easy to spot and sort out.
Incidentally, although melt layers are more common at lower elevations, melt
layers only show up in GISP2 about once/century.
His third argument that storms have warm and cold oscillations that can
produce layers is, I believe another half-truth. Ordinary storms do not
produce hoar frost layers nor significant differences in electrical
conductivity or dust content. If they did, they would show up as countable
layers over the last 2000 years, which even Oard admits has not happened.
Snow dunes and large deposits of snow from very large storms can confuse the
visual counting of the annual hoar frost layers; but, these are rare events;
and I believe they do not effect the electrical conductivity or dust content
methods of counting the annual layers; so, they would be discovered and
discounted. I might add that in the top 40,000 layers (back to c. 38,000
B.C.) there is a very high agreement between these three independent methods
of counting the annual layers.
Oard's final argument that there are cycles of weather which can interfere
with the annual layers is again a half-truth. Where one method is confused by
such a change, one or more of the other methods exposes the error.
In the end Oard's arguments rest solely on his hypothesized "model" which
readily accepts the possibility of added layers per year, but does not take
into account the equal possibility of missing layers. The whole thing is as
usual special pleading.
The quickest overview of the GISP2 ice core (the main one) can be found in
Richard B. Alley and Michael Bender, "Greenland Ice Cores: Frozen in Time,"
Scientific American, February, 1998, 81 ff. A more thorough but still easy to
read and relatively short description is found in Richard B. Alley, _The Two
Mile Time Machine_ (Princeton: Princeton University Press, 2000). Some good
photographs of ice cores are in Kendrick Taylor, "Rapid Climate Change,"
American Scientist, 87 (July-Aug, 1999) 320-322. The articles by Meese et al
and by Alley cited by Oard are good sources if you are even more interested.
Paul
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