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.
Peter Olsen and Zachary Sharp, both from the University of New Mexico in Albuquerque, used the modern helium-3 leak rate to estimate how much of it might still be sitting inside the Earth’s core today. Their results, published in Geochemistry, Geophysics, Geosystems, indicate the core still contains a vast reservoir of helium-3 (up to a petagram – 1015grams).
According to Olsen and Sharp, the most likely way for our planet to acquire such high quantities of the gas within its interior is for Earth to have formed deep within an active solar nebula – not on its fringes or in a waning nebula.
Finding other nebula-created gases, such as hydrogen, leaking at similar rates and from similar locations will help to strengthen the evidence.