Helium-3 - all is not lost

Sep 03, 2005

Is there a reservoir of primordial rock deep within the Earth, left over from the birth of our planet? Geochemical data have traditionally indicated 'yes', but evidence from seismology seemed inconsistent with the survival of such a reservoir. This week in Nature, Cornelia Class and Steven Goldstein present a theory that may allow geologists to resolve this contradiction.

The question arose because the rocks of ocean islands like Hawaii contain relatively large amounts of helium-3, an isotope that must be mainly left over from the days when the Earth first formed, because it is not generated from the radiogenic decay of other elements. Researchers believed that helium-3-rich minerals should only come from untouched primordial rock that has welled up from deep within the mantle and has not previously been 'degassed' when partially melted near the Earth's surface.

But seismologists look upon this evidence with dismay. They see no evidence that large portions of the mantle have escaped the mixing and melting that drives plate tectonics and makes volcanoes.

Class and Goldstein show that the other minerals in ocean island rocks tell a different story - the most helium-3-rich rocks also contain elements that resemble the composition of rock that has melted before, such as that found at mid-ocean ridges. The best explanation for all this, they say, is simply that the mantle loses less of its helium than expected during melting. Their model, which will need physical experiments to back it up, explains how this might happen. A News and Views article by William M. White accompanies this research.

Source: Nature Publishing Group

Explore further: India tests long-range missile from mobile launcher

add to favorites email to friend print save as pdf

Related Stories

Gully patterns document Martian climate cycles

Jan 28, 2015

Geologists from Brown University have found new evidence that glacier-like ice deposits advanced and retreated multiple times in the midlatitude regions of Mars in the relatively recent past.

Super-Earths have long-lasting oceans

Jan 05, 2015

For life as we know it to develop on other planets, those planets would need liquid water, or oceans. Geologic evidence suggests that Earth's oceans have existed for nearly the entire history of our world. ...

Professor researches rare rock with 30,000 diamonds

Jan 05, 2015

Diamonds are beautiful and enigmatic. Though chemical reactions that create the highly coveted sparkles still remain a mystery, a professor from the University of Tennessee, Knoxville, is studying a rare ...

Recommended for you

Japan launches new spy satellite

11 hours ago

Japan on Sunday successfully launched a back-up spy satellite, its aerospace agency said, after cancelling an earlier lift-off due to bad weather.

NASA launches satellite to measure soil moisture

11 hours ago

NASA on Saturday launched a new Earth-observing satellite that aims to give scientists high-resolution maps showing how much moisture lies in soil in order to improve climate forecasts.

Planck: Gravitational waves remain elusive

Jan 30, 2015

Despite earlier reports of a possible detection, a joint analysis of data from ESA's Planck satellite and the ground-based BICEP2 and Keck Array experiments has found no conclusive evidence of primordial ...

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.