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: Innovative use of pressurant extends MESSENGER's mission, enables collection of new data

add to favorites email to friend print save as pdf

Related Stories

How was the Earth formed?

Dec 10, 2014

Just how did the Earth—our home and the place where life as we know it evolved—come to be created in the first place? In some fiery furnace atop a great mountain? On some divine forge with the hammer ...

And now, the volcano forecast

Oct 22, 2014

Scientists are using volcanic gases to understand how volcanoes work, and as the basis of a hazard-warning forecast system.

Recommended for you

The top 101 astronomical events to watch for in 2015

Dec 24, 2014

Now in its seventh year of compilation and the second year running on Universe Today, we're proud to feature our list of astronomical happenings for the coming year. Print it, bookmark it, hang it on your ...

NASA image: Frosty slopes on Mars

Dec 24, 2014

This image of an area on the surface of Mars, approximately 1.5 by 3 kilometers in size, shows frosted gullies on a south-facing slope within a crater.

Can astronomy explain the biblical Star of Bethlehem?

Dec 24, 2014

Bright stars top Christmas trees in Christian homes around much of the world. The faithful sing about the Star of Wonder that guided the wise men to a manger in the little town of Bethlehem, where Jesus was ...

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.