The deepest sections of the core are composed of water that fell as snow 
160,000 years ago. Scientists in Grenoble, France, fractured portions of the core and
measured the composition of ancient air released from bubbles in the ice. 
Instruments were used to measure the ratio of certain isotopes in the frozen water to 
get an idea of the prevailing atmospheric temperature at the time when that 
particular bit of water became locked in the glacier.