It seems the Vostok ice core extracted from the Antarctic ice sheet goes back around 700,000 years – and even this is a calculation based on a number of variabilities. It came to an end near the rock basement. I can remember reading something similar about a Greenland ice core – so what is actually going on. The Antarctic ice sheet is thought to be immeasurably older – by millions of years. It is thought old ice is squeezed laterally away towards the sea – to melt. Deep ice cores are taken at 'ice divides' where sideways motion is at a minimum – but as dividers move around with changing climate it is probably a difficult exercise to locate the older ice deposits. There are also 'blue ice' regions where older ice has been lodged up against mountains or ridges in the basement rock. However, as yet the oldest blue ice found so far is just 500,000 years old (so what does this mean in the context of a 700,00 year core?). In principle there is blue ice somewhere in the Antarctic that is as old as the ice sheet – some 15 million years of age.
The above is extracted from the comments section at the bottom of a post at http://wattsupwiththat.com/2011/06/01/radar-mapping-reveals-ancient-anta… and is well worth reading – as some little things not usually spoken in the scientific literature on the subject are aired – as well as commentators confused by it all. A lot of questions were raised and there are some knowledgeable replies that are useful in the grand scheme of things. What surprised me was that the ice cores were severely limited in relation to the age of the ice sheet – and that is from an orthodox perspective. It seems the age of the ice sheet is based on geochronology – and some other assumptions.