# When Earth formed 4.5 × 10⁹ years ago, how much radiation did surface rocks emit?

When Earth formed $$\approx 4.5 \times 10^9$$ years ago, Earth's surface rocks emitted more radiation because they had more unstable isotopes. All short half-life isotopes decayed long ago, and the amount of long half-life isotopes has decreased. How much radiation did rocks emit $$\approx 4.5 \times 10^9$$ years ago?

• By "how much radiation" do you mean power eg., Watts? Jun 12, 2020 at 2:24
• Sievert or grey
– Châu
Jun 12, 2020 at 8:42
• A little broad the question, includes crustal evolution, and has a wrong premise (some half lifes are in the billions of years). Earth's mantle and crust "mixed" heavily back in the day. Becaue of thet, could an answer be tackled indirectly via projecting thermal evolution ? That'll be a lot of work, though ... and i think the distribution of radiogenic stuff in the mantle is still a bit unclear ?
– user20217
Jun 12, 2020 at 9:52
• I think it is hard to answer. For example, imagine if there is any isotope X, which decays quickly into X', which is a major component of the crust. How can you say, how much of it was there 4.5bln year ago? I think there is no way for that. However, I believe realistic estimations should exist, using partially stellar models and astronomical results. I vote "leave open". Jun 12, 2020 at 20:11