Terrawatch: Rare gas points to deep nebula origins for Earth

Most of rare isotope of helium found on mid-ocean ridges dates to big bang, providing clue to planet's formation

A rare isotope of helium, bubbling up along mid-ocean ridges, is proving to be a vital clue to our planet's origins.

Just 2kg of helium-3 - enough to fill a balloon the size of your desk - leaks out of the Earth each year. Very little of this rare isotope is produced on the Earth's surface today, and most of it dates to the big bang, where it would have been incorporated into planets as they grew out of the dust and debris spinning around the early sun.