If we want to reconstruct past air temperatures, one of the most critical parameters is the age of the ice being analysed. Fortunately, ice cores preserve annual layers, making it simple to date the ice. Seasonal differences in the snow properties create layers – just like rings in trees. This section of the ice core contains 28 annual layers with summer layers sandwiched between darker winter layers. The thickness of the annual layers in ice cores can be used to derive a precipitation rate, which is essential parameter for many past climate studies.

Sometimes researchers are studying actual bubbles of the early atmosphere, trapped in the ice as it formed. Scientists run melted samples through various instruments to find tiny pieces of pollution, like sulfates, traces of metals, or natural aerosols like dust or volcanic ash . After analyzing enough ice core slices, a researcher can look for patterns to track changes in the atmosphere's composition and temperature.