Asked by Chris
Hi Chris,
We only know the age of ice by looking at its context. Just like you can’t know how old a pebble you find on the beach is without knowing its geological stratigraphic context, we need to look at the whole ice column to work out how old an individual air bubble is.
One of the key ways in which ice is dated is by taking a long ice core and counting the annual layers. Ice forms distinctive annual layers, like tree rings – so by counting the number of layers, you would know how old the air in the bubble was.
As you go deeper into the ice core, you need to use other methods to calculate age – such as layers of volcanic ash from known eruptions, radiometric dating, geochemistry, electrical conductivity and by applying numerical models and account for glacier flow.