At least 1.5 billion years after it last saw the surface, flowing liquid may host life.

Chance more than doubled that capital city will soon experience big temblor, researchers calculate. (p. 20)

At 400 parts per million, greenhouse gas concentration is now higher than it has been for millions of years. (p. 20)

DENVER — “I’m a little tired of the cold,” Geoff Hargreaves says with a sigh. No surprise there: Hargreaves works in a deep freeze — 38 degrees Celsius below zero (−36° F). As curator of the National Ice Core Laboratory, his job is to keep ice cores from Antarctica and Greenland frozen. These cylinders — which would stretch more than 17,000 meters if laid end-to-end — are precious. They contain records of past climate and atmospheric chemistry, trapped in tiny bubbles that formed thousands of years ago and froze in chronological layers like tree rings. Melting is the enemy, ... (p. 32)