Re dating. Someone asked for a baseline. We have that. Glacial ice forms annual layers, which we observe year by year as it happens. When cores are cut from the glacial ice, we can count back those layers. Cores from Antarctica already go back many millions of years.
Carbon dating is only good back for 50,000 years. However, what we can do, and have done, is to carbon date the bits of organic debris that get caught up in ice cores. Since the place in that ice core can be dated simply by counting back the annual layers, we know how old the organic item is. If the carbon dating matches, then carbon dating is valid. And it is.
This didn't sound right, I was picturing a guy counting a million layers of ice trying to guess the count when they got all jumbled together deep in the core, so I had to look this up.
You can't simply count a million years because of ice flow and high pressure, it can't be done with annual layers, they become unreadable just as I thought:
Shallow cores, or the upper parts of cores in high-accumulation areas, can be dated exactly by counting individual layers, each representing a year. These layers may be visible, related to the nature of the ice; or they may be chemical, related to differential transport in different seasons; or they may be isotopic, reflecting the annual temperature signal (for example, snow from colder periods has less of the heavier isotopes of H and O). Deeper into the core the layers thin out due to ice flow and high pressure and eventually individual years cannot be distinguished.
Instead of counting visible layers we use a variety of dating methods. One of them is to look for material that is from a known and dated event, like a volcanic eruption.
http://en.wikipedia.org/wiki/Ice_core
There are many different dating methods for these ice cores which produce different results, but the point is that they all are to varying degree inaccurate, as much as 10,000 years inconsistent. But, they are precise and we can tell if something is older than something else.
http://en.wikipedia.org/wiki/Ice_core
Ice cores cannot be used as a baseline, because they require dating themselves once annual layers become undistinguishable. These ice core dating methods, just like other dating methods, become more inaccurate the further back in time you go. This is in part because of the variance in the environment that we don't know of.
We need a sample of material that has the date stamped on it. That's not going to happen, but maybe in the future we will have a more accurate method to date material.
The oldest to-date ice core that I could find dates around 800,000 years, not millions of years like you said.
http://www.nature.com/nature/journal/v429/n6992/full/429611a.html
Of course there are some newer samples than this one, but they are still being analyzed.
To the point, we can't use ice cores to calibrate carbon dating when carbon dating is used to calibrate ice core dating. Every ice core is different, and when you get past the visible annual layers, we have to use a dating method none of which are so accurate. Dating anything is still an estimated guess without baseline materials that have actual dates.
