Abstract
The Earth has cooled since its formation, yet the decay of radiogenic isotopes, and in particular uranium, thorium and potassium, in the planet’s interior provides a continuing heat source. The current total heat flux from the Earth to space is 44.2±1.0 TW, but the relative contributions from residual primordial heat and radiogenic decay remain uncertain. However, radiogenic decay can be estimated from the flux of geoneutrinos, electrically neutral particles that are emitted during radioactive decay and can pass through the Earth virtually unaffected. Here we combine precise measurements of the geoneutrino flux from the Kamioka Liquid-Scintillator Antineutrino Detector, Japan, with existing measurements from the Borexino detector, Italy. We find that decay of uranium-238 and thorium-232 together contribute
TW to Earth’s heat flux. The neutrinos emitted from the decay of potassium-40 are below the limits of detection in our experiments, but are known to contribute 4 TW. Taken together, our observations indicate that heat from radioactive decay contributes about half of Earth’s total heat flux. We therefore conclude that Earth’s primordial heat supply has not yet been exhausted.
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Acknowledgements
We thank E. Ohtani and W. F. McDonough for advice and guidance. The KamLAND experiment is supported by a Grant-in-Aid for Specially Promoted Research under grant 16002002 of the Japanese Ministry of Education, Culture, Sports, Science and Technology; the World Premier International Research Center Initiative (WPI Initiative), MEXT, Japan; and the US Department of Energy (DOE) grants DEFG03-00ER41138 and DE-AC02-05CH11231, as well as other DOE grants to individual institutions. The reactor data are provided by courtesy of the following electric associations in Japan: Hokkaido, Tohoku, Tokyo, Hokuriku, Chubu, Kansai, Chugoku, Shikoku and Kyushu Electric Power Companies, Japan Atomic Power Company and Japan Atomic Energy Agency. The Kamioka Mining and Smelting Company has provided service for activities in the mine.
Author information
Affiliations
Research Center for Neutrino Science, Tohoku University, Sendai 980-8578, Japan
- A. Gando
- , Y. Gando
- , K. Ichimura
- , H. Ikeda
- , K. Inoue
- , Y. Kibe
- , Y. Kishimoto
- , M. Koga
- , Y. Minekawa
- , T. Mitsui
- , T. Morikawa
- , N. Nagai
- , K. Nakajima
- , K. Nakamura
- , K. Narita
- , I. Shimizu
- , Y. Shimizu
- , J. Shirai
- , F. Suekane
- , A. Suzuki
- , H. Takahashi
- , N. Takahashi
- , Y. Takemoto
- , K. Tamae
- , H. Watanabe
- , B. D. Xu
- , H. Yabumoto
- , H. Yoshida
- & S. Yoshida
Institute for the Physics and Mathematics of the Universe, Tokyo University, Kashiwa 277-8568, Japan
- K. Inoue
- , M. Koga
- , K. Nakamura
- , S. Enomoto
- , A. Kozlov
- , H. Murayama
- , A. Piepke
- , S. J. Freedman
- , B. K. Fujikawa
- , G. A. Horton-Smith
- , Y. Efremenko
- , K. M. Heeger
- & M. P. Decowski
Physics Department, University of California, Berkeley and Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
- H. Murayama
- , T. I. Banks
- , T. Bloxham
- , J. A. Detwiler
- , S. J. Freedman
- , B. K. Fujikawa
- , K. Han
- , R. Kadel
- , T. O’Donnell
- & H. M. Steiner
Department of Physics and Astronomy, University of Alabama, Tuscaloosa, Alabama 35487, USA
- C. Grant
- , G. Keefer
- & A. Piepke
W. K. Kellogg Radiation Laboratory, California Institute of Technology, Pasadena, California 91125, USA
- D. A. Dwyer
- , R. D. McKeown
- & C. Zhang
Department of Physics, Colorado State University, Fort Collins, Colorado 80523, USA
- B. E. Berger
Physics Department, Drexel University, Philadelphia, Pennsylvania 19104, USA
- C. E. Lane
- , J. Maricic
- & T. Miletic
Department of Physics and Astronomy, University of Hawaii at Manoa, Honolulu, Hawaii 96822, USA
- M. Batygov
- , J. G. Learned
- , S. Matsuno
- & M. Sakai
Department of Physics, Kansas State University, Manhattan, Kansas 66506, USA
- G. A. Horton-Smith
Physics Department, Stanford University, Stanford, California 94305, USA
- K. E. Downum
- , G. Gratta
- & K. Tolich
Department of Physics and Astronomy, University of Tennessee, Knoxville, Tennessee 37996, USA
- Y. Efremenko
- & O. Perevozchikov
Triangle Universities Nuclear Laboratory, Durham, North Carolina 27708, USA
- H. J. Karwowski
- , D. M. Markoff
- & W. Tornow
Physics Departments at Duke University, North Carolina Central University, and the University of North Carolina at Chapel Hill, USA
- H. J. Karwowski
- , D. M. Markoff
- & W. Tornow
Department of Physics, University of Wisconsin, Madison, Wisconsin 53706, USA
- K. M. Heeger
Nikhef, Science Park 105, 1098 XG Amsterdam, The Netherlands
- M. P. Decowski
Consortia
The KamLAND Collaboration
- Research Center for Neutrino Science, Tohoku University
- A. Gando
- , Y. Gando
- , K. Ichimura
- , H. Ikeda
- , K. Inoue
- , Y. Kibe
- , Y. Kishimoto
- , M. Koga
- , Y. Minekawa
- , T. Mitsui
- , T. Morikawa
- , N. Nagai
- , K. Nakajima
- , K. Nakamura
- , K. Narita
- , I. Shimizu
- , Y. Shimizu
- , J. Shirai
- , F. Suekane
- , A. Suzuki
- , H. Takahashi
- , N. Takahashi
- , Y. Takemoto
- , K. Tamae
- , H. Watanabe
- , B. D. Xu
- , H. Yabumoto
- , H. Yoshida
- , S. Yoshida
- , S. Enomoto
- , A. Kozlov
- , H. Murayama
- , C. Grant
- , G. Keefer
- , A. Piepke
- , T. I. Banks
- , T. Bloxham
- , J. A. Detwiler
- , S. J. Freedman
- , B. K. Fujikawa
- , K. Han
- , R. Kadel
- , T. O’Donnell
- , H. M. Steiner
- , D. A. Dwyer
- , R. D. McKeown
- , C. Zhang
- , B. E. Berger
- , C. E. Lane
- , J. Maricic
- , T. Miletic
- , M. Batygov
- , J. G. Learned
- , S. Matsuno
- , M. Sakai
- , G. A. Horton-Smith
- , K. E. Downum
- , G. Gratta
- , K. Tolich
- , Y. Efremenko
- , O. Perevozchikov
- , H. J. Karwowski
- , D. M. Markoff
- , W. Tornow
- , K. M. Heeger
- & M. P. Decowski
Authors
Contributions
All authors contributed equally to the work presented in this study.
Competing interests
The author declare no competing financial interests.
Corresponding author
Correspondence to I. Shimizu.
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