Earth's oceans may once have frozen solid, pole to pole
Geological evidence suggests Earth's oceans may once have frozen over almost completely, possibly more than once, for episodes lasting millions of years. Geobiologist Joseph Kirschvink coined the term 'Snowball Earth' in 1992 after tracing glacial rock deposits across continents that sat near the equator at the time. A runaway feedback loop, ice reflecting away sunlight and making still more ice, may have broken only once volcanic CO2 built up enough to thaw the planet.