But Japanese researchers have made a compelling case that Earth's oceans were once green, in a study published in Nature. The reason Earth's oceans may have looked different in the ancient past is ...

Astronomers tallying up all the normal matter—stars, galaxies and gas—in the universe ... years of Earth—and measuring the slight dimming or brightening of the cosmic microwave background ...

Related: ISS astronaut captures green auroras dancing over city lights (video) Pettit, 69, is NASA's oldest active astronaut. He's known to space enthusiasts for his off-Earth photography and ...