- Beryllium-10 is an isotope that is a proxy for the sun's activity. Be10 is produced in the atmosphere by cosmic ray collisions with atoms of oxygen and nitrogen. Beryllium 10 concentrations are linked to cosmic ray intensity which can be a proxy for solar strength.
One way to capture earth's record of that proxy data is to drill deep ice cores. Greenland, due to having a large and relatively stable deep ice sheet is often the target for drilling ice cores.
Isotopic analysis of the ice in the core can be linked to temperature and global sea level variations. Analysis of the air contained in bubbles in the ice can reveal the palaeocomposition of the atmosphere, in particular CO2 variations. Volcanic eruptions leave identifiable ash layers.
While it sounds simple to analyze, there are issues of ice compression, flow, and other factors that must be taken into consideration when doing reconstructions from such data. I attended a talk at ICCC 09 that showed one of the ice core operations had procedures that left significant contamination issues for CO2. But since Beryllium is rather rare, it doesn't seem to have the same contamination issues attached.