© Lloyd, Charles Chandler

 

EARTH HEAT
The only substantial heat sources for the Earth are from the decay of radioactive elements and heat from the giant impacts of accretion. Because Earth's radioactive elements are concentrated near the surface, heat from this source is rapidly dissipated and does not accumulate. Yet the measured heat loss from the Earth is far greater than that produced by Earth's radioactive elements. To be specific, about 24 terawatts of heat are produced by radioactive elements in the Earth, while measured heat loss from the Earth is about 44 terawatts.16 Geophysicists speculate that there must be an insulated heat reservoir deep in the Earth releasing the rest of the measured heat over billions of years. However, it is more reasonable that the extra heat is primordial heat from the giant impacts of accretion, and that the Earth is much younger.

RAPID PLANETARY SOLIDIFICATION
Once it has finished accreting, the cooling and solidifying of a rocky planet such as the Moon happens very quickly for the first 80%, lasting only a matter of 1000 years. Cooling and solidifying the final 20% lasts on the order of some millions of years, during which the crustal lid on top is separated from the crystallizing mantle below by a thin fluid layer. The Moon may have taken 10 million years to cool.5 The Earth is much larger than the Moon, and so might take longer to cool. But Earth still has a low-viscosity layer between the crust and upper mantle called the asthenosphere, indicating that Earth is in the latter stages of cooling. Thus the age of Earth since accretion should be in the millions, rather than billions, of years.