If by "core" - you mean to exclude the mantle, then yes, we don't know exactly how much radiogenic [1] heat generation there is. But if we are using the term "

If by "core" - you mean to exclude the mantle, then yes, we don't know exactly how much radiogenic [1] heat generation there is. But if we are using the term "core" loosely here to refer to everything under the crust, then a very significant fraction of the heat is generated via radioactive decay. [1] https://en.wikipedia.org/wiki/Earth's_internal_heat_budget#Global_internal_heat_flow https://en.wikipedia.org/wiki/Earth's_internal_heat_budget#G...