Question

Soon after Earth was formed, heat released by the decay of radioactive elements raised the average internal temperature from 300 to 3000 K, at about which value it remains today. Assuming an average coefficient of volume expansion of 2.9 × 10–5 K–1, by how much has the radius of Earth increased since the planet was formed?

Answer 1

r(now) = r(then) [ 1 + (1/3) (coeff of volume expansion) (3000-300)]

express as r(now)-r(then)
or r(now)/r(then)