Which combination of energy sources was primarily responsible for generating the heat that allowed early Earth to differentiate?
ASolar radiation absorbed at the surface, which gradually melted the interior over billions of years.
BOnly long-lived radioactive isotopes like U-238 and Th-232, which have always been the dominant heat source.
CGravitational potential energy released as dense material sank, plus decay of short-lived radioisotopes like Al-26.
DTidal heating from the early Moon, similar to how Io is heated by Jupiter today.
The early solar system contained abundant short-lived radioisotopes (especially Al-26, with a half-life of ~0.7 Myr) that released enormous heat before decaying away. Simultaneously, the energy released as dense iron sank through lighter silicates — converting gravitational potential energy to heat — provided additional melting. Together, these made wholesale differentiation possible within the first few tens of millions of years.
Question 2 True / False
Most asteroids in the solar system are undifferentiated primitive bodies that preserve the original composition of the solar nebula.
TTrue
FFalse
Answer: False
Several asteroid parent bodies, including the Vesta-family and the parent bodies of iron meteorites, underwent differentiation. Iron meteorites are essentially the exposed cores of destroyed differentiated planetesimals. The existence of differentiated asteroids shows that even relatively small bodies can differentiate if they form early enough to contain sufficient Al-26.
Question 3 Short Answer
Why do larger planets differentiate more completely than smaller bodies like asteroids?
Think about your answer, then reveal below.
Model answer: Larger bodies accumulate more heat from accretion and radioactive decay, and their greater mass provides stronger gravitational driving for density separation. Crucially, they retain heat longer because they have a smaller surface-area-to-volume ratio, keeping the interior molten for millions of years while density sorting occurs. Smaller bodies cool too quickly for complete separation.
The surface-area-to-volume argument is key: a small asteroid radiates heat away faster relative to its volume and freezes solid before iron can fully sink. Large planets stay hot long enough for differentiation to go to completion. This is why small meteorite parent bodies show partial differentiation while Earth, Mars, and the Moon each have a distinct core, mantle, and crust.