© Ken McGee/U.S. Geological Survey
Plumes of steam rise up from many spots along the Firehole River in Yellowstone National Park.
Yellowstone National Park's geysers, hot springs, fumaroles and other hydrothermal features
spew out a collection of gases
from deep within the Earth - steam, carbon dioxide, methane, neon, argon and helium. There's not enough of that last one, helium, for the park to start selling balloons or for visitors to sound like chipmunks
, but there's plenty for scientists to study.
Helium can bubble out of volcanic rocks that drive hydrothermal activity, but that's not where most of Yellowstone's helium is coming from, it seems. The park's gas originates deep in rocks where it's been stored for hundreds of millions of years, U.S. Geological Survey scientists report
today in Nature
Helium is the second-most abundant element in the universe - it's formed by the nuclear fusion of hydrogen atoms, a process that powers stars
- but it's pretty rare here on Earth. Lucky for birthday-party goers and clowns (and modern medicine
), helium can be extracted from reserves of natural gas
Helium on Earth can be found in two main forms
: Nearly all occurs as helium-4 (named thus because it has two protons and two neutrons), which can be produced during the radioactive decay
of heavy elements such as uranium. A tiny fraction (about one in a million) occurs as helium-3
(two protons and one neutron), most of which has been present on Earth since the planet's formation and is a vestige of material that originally formed the planet.