1. Radioactive decay: Radioactive elements such as uranium, thorium, and potassium decay and emit heat as a byproduct. This heat is generated deep within the Earth's interior and is responsible for about 20% of the total surface heat flux.

2. Primordial heat: This is the heat that remains from the Earth's formation about 4.5 billion years ago. As the Earth accreted from smaller bodies, the energy of impacts and compression generated a tremendous amount of heat. Some of this heat was lost to space, but a significant portion remains trapped within the Earth's interior. Primordial heat contributes about 80% of the total surface heat flux.

Therefore, primordial heat has a greater contribution to the surface flux compared to radioactive decay.