All of the radioactive elements that made up the early Earth started out in the hot ash of ancient supernova explosions. This means we’ve been working through their half-lives for at least 5 billion years since our planet was born. How much hotter was Earth’s interior then? What would the heat from nuclear reactions mean for tectonic activity and the evolution of life in our world’s feverish youth?
• An earlier answer to this question said Earth’s internal heat is generated by the radioactive decay of uranium, thorium and potassium. There was, however, no mention of the gravitational heating caused…
