Trilobites and 95 percent of marine creatures went the "way of the dinosaurs" during the Permian extinction, millions of years before dinosaurs existed.
Geologists posit that Earth was once entirely covered by ice.
Data from the Rosetta mission, the Mars rover and the Herschel space observatory point to water's extraterrestrial origins.
*Beware of alarmist headlines. The odds are slim when it comes to giant Earth-bound asteroids.
Most of us take our oxygen-rich atmosphere for granted. Once upon a time, though, Earth's air was very different.
Scientists have gathered detailed data measuring light from over 2,000 galaxies, some of which are up to several billion light years away from earth.
According to another theory, life on Earth may not have begun with RNA but rather with amino acids able to fold into proteins in a high salt environment.
One of the great mysteries: Does life exist elsewhere in the universe. Research has found that such planets may be more common, and much closer, than we think.
The Kepler space telescope has shown us that we live in a galaxy full of Earth-sized planets.