Ice Core Dating: The Invisible Years
How old you think the lower part of the ice cores are, will depend in part on what theory of ice age you’ve adopted, how many ice ages are part of that particular theory and how long you think annual layering has followed recently observed patterns. The farther down the core, the more difficult it is to count what are perceived to be annual layers. One example of this difficulty is the case of the missing 25,000 years. At 2800 meters, the ice in the Vostok core was believed to be around 110,000 years old, based on sea core chronology. However the Gisp2 ice core at 2800 meters, when compared to the Vostok, was found to be missing 25000 years. This is a huge chunk of time and the layers had supposedly been carefully counted by different methods that were said to assure accuracy.
This did not prove an insurmountable problem to the scientists involved, however. Just as pollen counts and sea core chronology had been massaged in other cases to fit new and radically different interpretations, so could the layer count be revised to better fit the Vostok chronology. By changing from an 8mm wide laser beam to a 1mm wide laser beam, 25000 previously invisible annual layers were “discovered.” (Meese, D.A., 26417). The problem was thus ‘solved’ and the two cores could now be said to ‘be in agreement’ and used to reinforce the validity of the current theory of ice core interpretation to the general public.
However it would appear that annual layer identification can be just as subjective or plastic as pollen counts and sea core correlation and not the ‘absolute dating method’ it’s often touted to be in the popular science articles and textbooks. And you have to wonder, if they could find an extra 25,000 years in just a few meters of ice core by changing the size of the laser beam, how many layers (years) could be added to the core if the entire bottom half was measured by the 1mm beam? If there hadn’t been a discrepancy between the two cores, then apparently the need to switch laser sizes would have been deemed unnecessary and the 25000 years would have remained invisible and uncounted. The cores would still have been said to “be in accord”. What would we do with out the scientific method?