otseng wrote:micatala wrote:
I also note that in this picture we still see light layers and darker layers on all the walls. In the firstpicture you provided you could see multiple layers but of similar colors. Especially if and when the layers get compressed, the differences would be enhanced.
As I've
cited, an "annual layer" is 1 cm thick. Refering to the original photo below with the scale on the right, we would be viewing over 150 years of snow deposits.
Just to clarify slightly, the quote is that the annual layers are "about" 1 cm thick.
otseng wrote:
We have yet to even demonstrate how to even visually arrive at a date. Yes, you have mentioned that scientists have been studying ice layer formation over 50 years ago, but when we look at the data from actual ice core sites, there are a wide array of interpretations on what exactly is an annual layer. Granted we are not professionals, but there should at least exist some objective standard of how an annual layer is visually determined. Several proposals have been offered. Is it one dark/light band? Is it several dark/light bands?
First, let's be clear where an ambiguity lies. I am not an expert and so am not going to pretend to be. If I have been ambiguous in my statements, or if my statements disagree with grumpy's or nygreenguy's or scotracer's, this confusion should not be attributed to the experts.
In a previous link you posted, there seems to be a fairly unambiguous criteria offered.
http://www.k5geosource.org/content/dd/climate/pg6.html wrote:
Three deep core sections show distinct annual bands produced by the deposition of dust during the dry season (dry season dust layers are represented by triangles). While annual bands provide accurate relative dating (the age of each ice band is known to be a year apart from directly adjacent bands), paleoclimatologists also search for absolute dates within a core chronology. Electrical conductivity measurements (ECM), particle concentrations, and the ratio of heavy to light oxygen molecules are other seasonally-variable core parameters that can be used along with visual stratigraphy in dating ice cores.
All the direct quotes that I can recall from scientists have side light ice is from the winter, dark is from the summer. If there were any confusion among scientists, they could double check this through O16/O18 isotope testing or, as in this case, look for the inclusion of dust.
otseng wrote:micatala wrote:1) Despite numerous cross checking methods and ongoing current observations, scientists cannot even count the layers they have seen forming accurately.
If they can count it, then it should be explainable in clear terms to us laymen. There should be no ambiguity and have a clear definition.
Here is the larger context from the
post of mine quoted. #691
micatala wrote:
In order for ice core dating to be drastically wrong, it seems to me you need to prove or assume one or more of the following:
1) Despite numerous cross checking methods and ongoing current observations, scientists cannot even count the layers they have seen forming accurately.
2) That, although ice core dating works for recent years, something changed at some point in the past that altered how the layers were formed and have led us to interpret as annual layers which are actually subannual. Whatever this "something" is does not seem to change the appearance or chemistry of the layers beyond what scientists have accounted.
Again, I might have been ambiguous, mostly because I am typically cautious not to overstate my case. I am not sure where any of the experts quoted have been ambiguous, but if this is the case, I'll ask otseng to correct me.
Now, if otseng is expecting those of us on the forum to be able to determine the annual layers from his images from WAIS, then I will insist on a couple of things.
The first is a confirmation of where these are from and that the 1 cm figure cited from the wikipedia article applies to the specific sites where the photos are from.
More importantly, if we ARE talking about 1 cm layers, then the resolution on these photos does not seem to me to be sufficient. I tried zooming in on the most recently included photo. As I did, I could see places where more layers were discernible. However, I also experienced some blurring.
The picture in the link I cited includes a pretty non-ambuguous set of layers, but the layers are also thicker than those at the WAIS site.
I also tried zooming in on the originally posted photo from
http://lima.nasa.gov/antarctica/. Once again, zooming revealed additional layers, but also blurring. My hypothesis is that we are seeing both annual layers that are very thin and longer climactic variations. I very cold winter could produce an exceptionally light band, and a warm summer an exceptionally dark. A warm period could result in the summer and winter layers being relatively darker.
I guess I'll ask you to clarify what you are expecting. I am willing to make an attempt to do what the experts do, but I also want it understood that my being unable to do this should not be taken to imply that the experts do not know how to determine annual layers.
I do not accept, for example, the assertion made in the next quote that the experts are not able to use visual stratigraphy to determine annual layers where that is appropriate.
otseng wrote:
For one thing, we are not able to establish how to visually determine an annual layer.
Also as one gets further deeper, visual and isotope dating becomes more difficult. Isotopes diffuses over time. Layers become more indistinguishable. If we see such thin layers in the Antarctic in the first 2 meters, then how thin would be the layers hundreds, thousands of meters deep?
First, I will point out that we have noted the average for the continent is 5 cm per year and for the Vostok area, 2.5 cm per year. So, layer thickness will vary from location to location.
As far as how far down we go before the layers become too thin to distinguish, I beleive one of the links you cited on WAIS noted they could go back 40,000 years. In other areas it might be more or less.
otseng wrote:I also note that otseng's own ball park figure based on sheet thickness gave an estimate of 44,000 years.
It was a ballpark figure based on numerous assumptions and to give the high end value of the age of the ice cap. I'm not offering my ballpark estimate as a firm date as to the age of the ice cap, rather simply an estimate based on several assumptions.
Understood. Averages can only be used in this way, unless we can verify the average DOES hold over the long term. I allow that my estimate of 132,000 years is not to be taken as conclusive. I would not say it is either "high end" or "low end" just an esimate that would hold if the assumptions were correct concerning the average of 2.5 cm over the long term.
otseng wrote:
micatala wrote:Would otseng agree that ice core data indicates with a high probability that no global flood occurred in the last 40,000 years?
I will agree that the age of the ice cap is a limiting factor to the dating of the flood. As to my 40,000 year estimate, I'm not offering that as an exact date for the flood.
Understood.
" . . . the line separating good and evil passes, not through states, nor between classes, nor between political parties either, but right through every human heart . . . ." Alexander Solzhenitsyn