ice stratifictation aging?

[Didymus]

Watched the Bill Nye vs. Ken Ham debate the other day, and one point was made I've never really looked in to: Bill Nye pointed to ice core layers showing hundreds of thousands of summer/winter cycles. This doesn't bother me because I'm rather confident the earth is old enough for that, but I approach all new information with what I consider to be a healthy dose of skepticism. Not everyone agrees with my unit f measurement, but that's irrelevant.

 

 

So, what is looked for in the ice to define a summer/winter cycle? Is it anything beyond simple stratification? Or are individual gas samples taken to look for seasonal changes?

 

Anyone able to link me to some good pictures showing such layers? How can we be sure each layer represents a summer/winter cicle as opposed to given layers brought by individual storms rather than year cycles?

[swansont]

http://en.wikipedia.org/wiki/Ice_core

 

http://www.google.com/search?q=ice+core+layers&tbm=isch&tbo=u&source=univ&sa=X&ei=3xn2UurLHtLI0gHyt4AQ&sqi=2&ved=0CCQQsAQ&biw=1821&bih=948