For the study, researchers removed the deeply buried samples using a drill core. "We're using a direct measurement and we're measuring from a mineral that has has actually trapped atmosphere. Canadian scientists have found a way to analyze air from the ancient Earth's atmosphere that was trapped in salt crystals nearly a billion years ago. Trapped bubblesWhen salty water called brine evaporates from a shallow pool, it forms crystals of salt called halite — very similar to the kind we sprinkle on our food. In the process, it often traps tiny bubbles of fluid or air from the atmosphere at the time it forms.

Source: CBC News July 28, 2016 16:41 UTC