Let's now consider the other uncertainty.
The concentration of radioactive nuclides in the mantle and
their influence on heat production over Earth history.
Because radiogenic elements decay,
the total quantity of radioactive nuclides in the bulk Earth has decreased over time.
But the mantle may have lost its radiogenic heat source proportionately
faster than expected from simple element decay rates.
Because most significant radioactive elements for heat production, that is 238
Uranium, 235 Uranium, 232 Thorium and 40 Potassium are all incompatible elements.
They'd rather be in continental crust than in mantle rock.
So if all the continental crust grew in the first 100 million years after
the formation of the Earth, there would be less radioactive isotopes to
heat the mantle than if continental crust has grown gradually over Earth's history.
Well, so how do we know which of these happened?
Well, this is another major discussion in geology.
The 4.4 billion-year-old Jack Hill zircons indicate that granite existed in
the early Hadean, and therefore, there must have been some continental crust,
almost immediately at the beginning of Earth history.
But the evidence of how much, and the timing of, and the rates at
which continents have grown since then, since the early Hadean, remains ambiguous.