How much of Earth's heat flow comes from radioactive decay?
In plain words
Earth loses about $4.6\mathrm{e}20\,\mathrm{erg}$ of heat each second through its surface, partly from decaying uranium, thorium and potassium and partly from heat left over from its formation. The split is measured with geoneutrinos (antineutrinos from radioactive decay inside Earth) and is still uncertain.
Precise statement
Surface heat loss is about $4.6 \times 10^{20}\,\mathrm{erg}/\mathrm{s}$. Borexino (Physical Review D 2020, arXiv:1909.02257) inferred mantle radiogenic power $2.5 \times 10^{20}\,(+1.1 \times 10^{20}, -1.0 \times 10^{20})\,\mathrm{erg}/\mathrm{s}$, total radiogenic power $3.8 \times 10^{20}\,(+1.4 \times 10^{20}, -1.3 \times 10^{20})\,\mathrm{erg}/\mathrm{s}$ and a convective Urey ratio (mantle radiogenic heat over mantle heat loss) of $0.78\,(+0.41, -0.28)$, while bulk-silicate-Earth composition models span roughly $10^{20}\ \text{to}\ 3 \times 10^{20}\,\mathrm{erg}/\mathrm{s}$ of total radiogenic power. Determine mantle radiogenic power with uncertainty below about $3 \times 10^{19}\,\mathrm{erg}/\mathrm{s}$ and identify which composition model holds.
What would settle it
Geoneutrino measurements at several sites including an ocean-bottom detector far from continental crust, combined with refined crustal U and Th models.
Status in the literature
Unverified note: it names recent work and was partly written without a live literature search; it awaits a check by an editor.
SNO+ reported the first Western Hemisphere geoneutrino flux, 49 (+13, -12) TNU, in 2026 (arXiv:2604.05746); the mantle term remains poorly constrained.
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