thorium
... that the radioactive decay of thorium produces a significant amount of the Earth's internal heat?
... that the <a href="./Radioactive_decay" id="mwBx4" rel="mw:WikiLink" title="Radioactive decay">radioactive decay</a> of <b id="mwBx8"><a href="./Thorium" id="mwByA" rel="mw:WikiLink" title="Thorium">thorium</a></b> produces a significant amount of the <a href="./Earth#Heat" id="mwByE" rel="mw:WikiLink" title="Earth">Earth's internal heat</a>?