Radioactive decay is key ingredient behind Earth's heat

Aug 02, 2011
Earth

Nearly half of the Earth's heat comes from the radioactive decay of materials inside, according to a large international research collaboration that includes a Kansas State University physicist.

Glenn Horton-Smith, associate professor of physics, was part of a team gathering some of the most precise measurements of the Earth's radioactivity to date by observing the activity of -- particularly uranium, thorium and potassium. Their work appears in the July issue of Nature Geoscience in the article "Partial radiogenic heat model for Earth revealed by geoneutrino measurements."

"It is a high enough precision measurement that we can make a good estimate of the total amount of heat being produced by these fissions going on in naturally occurring uranium and thorium," Horton-Smith said.

Itaru Shimizu of Tohoku University in Sendai, Japan, and collaborating physicists, including Horton-Smith, made the measurement using the KamLAND neutrino detector in Japan. KamLAND, short for Kamioka Liquid-Scintillator Antineutrino Detector, is an experiment at the Kamioka Observatory, an underground neutrino observatory in Toyama, Japan. Neutrinos are neutral that come from nuclear reactions or radioactive decay. Because of their small size, large detectors are needed to capture and measure them.

Horton-Smith was involved with developing the KamLAND detector from 1998 to 2000 and he helped prepare it to begin taking data in 2002. Several years later, he was involved in an upgrade of the detector to help it detect . For the most recent project, Horton-Smith's role was to help keep the detector running and taking measurements from nuclear reactors in Japan.

By gathering measurements of radioactive decay, the KamLAND researchers were able to observe geoneutrinos, or neutrinos from a geological source. They gathered data from 2002 to 2009 and had published their preliminary findings in Nature in 2005.

"That was the first time that observation of excess antineutrinos and a neutrino experiment were attributed to geoneutrinos," Horton-Smith said.

Previous research has shown that Earth's total heat output is about 44 terawatts, or 44 trillion watts. The KamLAND researchers found roughly half of that -- 29 terawatts -- comes from radioactive decay of uranium, thorium and other materials, meaning that about 50 percent of the earth's heat comes from geoneutrinos.

The researchers estimate that the other half of the earth's heat comes from primordial sources left over when the earth formed and from other sources of heat. Earth's heat is the cause behind plate movement, magnetic fields, volcanoes and seafloor spreading.

"These results helps geologists understand a model for the earth's interior," Horton-Smith said. "Understanding the earth's heat source and where it is being produced affects models for the earth's magnetic field, too."

The research also provides better insight for instances when materials within the earth undergo natural nuclear reactions. Based on their research, the physicists placed a five-terawatt limit on the heat cause by such reactions, meaning that if there is any geological heating from nuclear reactors in the Earth's core it is quite small when compared to heat from ordinary .

Explore further: Icelandic volcano sits on massive magma hot spot

Related Stories

What keeps the Earth cooking?

Jul 17, 2011

What spreads the sea floors and moves the continents? What melts iron in the outer core and enables the Earth's magnetic field? Heat. Geologists have used temperature measurements from more than 20,000 boreholes ...

Recommended for you

Icelandic volcano sits on massive magma hot spot

4 hours ago

Spectacular eruptions at Bárðarbunga volcano in central Iceland have been spewing lava continuously since Aug. 31. Massive amounts of erupting lava are connected to the destruction of supercontinents and ...

NASA sees Tropical Storm Ana still vigorous

6 hours ago

NASA's TRMM satellite saw that Tropical Storm Ana was still generating moderate rainfall is it pulled away from Hawaii. The next day, NASA's Aqua satellite saw that wind shear was having an effect on the ...

User comments : 15

Adjust slider to filter visible comments by rank

Display comments: newest first

avafeas
5 / 5 (2) Aug 02, 2011
29 out of 44 makes approximately 65%, not 50?
eigenbasis
5 / 5 (1) Aug 02, 2011
"meaning that about 50 percent of the earth's heat comes from geoneutrinos"

This sentence is completely inaccurate, the heat comes from the massive fragments of radioactive decays. Are they trying to say that the geoneutrinos interact so often that they account for 15TW of Earth's internal heat? That's a big stretch to state that
SCVGoodToGo
5 / 5 (5) Aug 02, 2011
Maybe the heat comes from Neutron Repulsion (tm) within the Earth's iron-neutronium core and everything around said core are waste products from neutron decay?

;)
DaveAW
3.5 / 5 (2) Aug 02, 2011
Uranium, Thorium and Potassium are subatomic particles?

Neutrinos need a big detector because they're small?

Really?
wwqq
5 / 5 (5) Aug 02, 2011
Uranium, Thorium and Potassium are subatomic particles?


Perhaps if you strip away all the electrons, but it's still an iffy thing to say that an atomic nucleus is a subatomic particle.

Neutrinos need a big detector because they're small?

Really?


Neutrinos need a big detector because they only interact through the weak force; their collision cross-section is very small. The mean-free path of a neutrino in lead is many light-years. The neutrino doesn't "see" the electromagnetic or strong nuclear force.
toyo
3.4 / 5 (8) Aug 02, 2011
Yet another sub-par article from this site.
I know the pressure to publish may sometimes get in the way of English expression, spelling or punctuation, but this site is based on reporting scientific articles!
You'd think that the editors(s?) might take the time to AT LEAST check the accuracy of the science!
A bit more pride in their work wouldn't go astray either...
MorituriMax
not rated yet Aug 02, 2011
Yet another nail in Neal Adam's Growing Earth "Theories."
TheGhostofOtto1923
3.4 / 5 (5) Aug 02, 2011
Yet another sub-par article from this site.
I know the pressure to publish may sometimes get in the way of English expression, spelling or punctuation, but this site is based on reporting scientific articles!
You'd think that the editors(s?) might take the time to AT LEAST check the accuracy of the science!
A bit more pride in their work wouldn't go astray either...
Yet another substandard comment from some buffoon too lazy to check the source of the article:
http://www.k-stat...211.html

-As you can see the news release was reprinted verbatim from the KSU website. Why don't you complain to them? Too lazy? Lights better over here at physorg?
Callippo
1 / 5 (5) Aug 02, 2011
I presume, the theory, the global warming is the result of the interaction of the Earth with dense cloud of dark matter (antineutrinos) doesn't sound so fantastic for many readers by now. Actually, it's the similar idea, like the theory presented in 2012 movie, which has been labeled as the worst sci-fi movie ever with NASA. I presume, the substantial part of this warming is the product of direct annihilation of these neutrinos with the matter of Earth.
martinplt
not rated yet Aug 02, 2011
So Thompson (later Lord Kelvin) famously calculated the age of the earth at a few million years based on simple cooling of a hot body. In doing so, he consciously posed an important question because geologists of the day already knew it was much older. All of us have since been taught "Ah ha! They didn't know about radioactive decay!"

So my question is, if it's not radioactivity and it's not heat capacity, then what is it?
Adam
5 / 5 (3) Aug 02, 2011
Hi martinplt
The real problem with Kelvin's heat-flow argument can be found in this GSA article from 2007... John Perry's neglected critique of Kelvin's age for the Earth: A missed opportunity in geodynamics http://www.colora...nity.pdf
...John Perry pointed out that Kelvin's assumption of constant thermal conductivity throughout the whole Earth was dubious and modifying it meant the observed heat-flow could be consistent with a multi-billion year age.
hush1
not rated yet Aug 03, 2011
Thks Adam. An astonishing correction of scientific history.
Perhaps water's density anomaly is not just unique to water.

Cores exhibiting such an anomaly changes any geodynamics.
What is the state (of matter) at the core? I don't know.
bamdadi
not rated yet Aug 06, 2011
I am not an expert. Please someone help me here.

What about the solar energy? There is no reference in this article to heat radiation originating from reflection/radiation of absorbed solar energy?
Y8Q412VBZP21010
5 / 5 (2) Aug 06, 2011
There is no reference in this article to heat radiation originating from reflection/radiation of absorbed solar energy?


Correct. The article simply discusses radioactive processes as producing Earth's heat OUTPUT. Solar
processes are an INPUT that will to an extent leak
back out again. This might be a kinda chilly planet if we didn't have the Sun.
Cave_Man
1 / 5 (1) Aug 08, 2011
So remember when they said 2012 was the most scientifically flawed movie ever or whatever.

Well there was an article back not so long ago that said there was a link between solar activity and radioactive decay, now this article says the heat in the core is radioactive decay.

So remind me again how 2012 is more flawed than idk The Matrix or Star Wars?