A New Theory of Earth Heating

In 1996 Walter Wagner proposed a fission explanation for the apparent steady state heat generation in the core of the Earth.

Abstract

The plate tectonics of the Earth are driven by heating within the Earth's core. The conventional theory of Earth heating suggests that the heat comes from radioactive decay deep within the Earth. Walter Wagner, an expert in nuclear physics, has formulated a new theory that says that this heat comes from a sustained fission reaction and from the radioactive decay of those fission products.

A Core within the Core

The Solar system was formed about 4.5 billion (4.5 × 10^9) years ago from a cloud of hydrogen that was slightly contaminated with heavier elements (which were created by a neutron capture mechanism during the super-nova of one or several predecessor stars). The heavier elements have a peak abundance in the iron-nickel range (Z = 26) with lesser abundances above and below that atomic number (due to the binding-energy/nucleon curve peaking at Z = 26).

As this contaminated hydrogen gas cloud contracted due to self-gravity it began to rotate due to intrinsic random angular momentum and to form internal centers of gravitational concentration. The largest center of gravitational concentration controlled the others and became our Sun. The other centers of gravitational concentration became balls of contaminated liquid hydrogen in orbit around the Sun. The heavier elements sank and the lighter elements rose within the balls. When the Sun ignited into a self-sustaining fusion reaction, the four liquid planets closest to the sun lost their lightest elements (hydrogen and helium).

The heaviest elements migrated toward the center of the Earth forming a metallic core, while the lighter silicates, aluminates, and other stony constituants formed the crust. It stands to reason that the heaviest elements of all such as gold, lead, thorium, and uranium had settled into a small (a few hundred miles in diameter) inner core.

Distance Moderation of Neutrons

The concentration of fissionable materials in the inner core can support a nuclear fission reaction if the energetic neutrons released in the process should be moderated to thermal velocity. In artificial reactors this is performed by surrounding the fuel elements by a light material with a low neutron capture cross section (such as helium, deuterium oxide (heavy water), light (ordinary) water, or graphite). In the Earth's core, no such light materials are available. However, the sheer distance involved (hundreds of miles) will slow the fast neutrons from multiple collisions with heavy nuclei.

The reaction will be self regulating because as the temperature of the inner core increases, the fission capture cross section of the fissile material in the core will decrease.

Due to a large amount of thorium 232 (and to a lesser extent uranium 238) in the inner core which have relatively large cross sections for thermal neutron capture, the inner core will slowly increase its content of fisionable material. This is because thorium 232 becomes thorium 233 upon neutron capture, which then beta decays to protactinium 233 and then to uranium 233, which is fissionable. Thus, the inner core will gradually increase its rate of heat production, and plate tectonic activity should increase over time.

Density Stratification in the Earth's Core

Due to the heat and pressure in the core of Earth, the metals there will not remain in solution with each other, but will segretate into shells sorted by density, with the densist metal, uranium, at the very center. Thorium is the next most dense metal and forms a spherical shell around the uranium. This is an ideal breeder reactor arrangement as distance-moderated thermal neutrons will be absorbed by the thorium nuclei. Less dense metals such as gold and lead form shells further up from the thorium. There will be some alloying of metals that have atomic densities (atomic mass divided by outer shell volume) within about one percent of each other.

Venus and Mars will have similar stratified cores. However, both those planets are smaller than Earth, and due to the gradual increase in nuclear activity in planets' cores because of fuel breeding, Earth is further along in this process and so now has tectonic activity while the smaller planets do not. It appears that the surface of Earth will re-melt in a few hundred million years, long before the sun becomes a red giant in a few billion years.

Meteors are fragments of planets shattered in collisions early in the solar system's formation. There are two broad classes of meteorites, nickel-iron and stony meteorites. If the core-stratification hypothesis is correct, then, based on the relative abundance of elements, one in a million meteorites should be gold. Fifteen years ago a 30 kg nugget of gold was found in the Australian desert, with no sign of nearby gold deposits.

Our model of planetary element stratification suggests that all the heavier elements in the crust have come from meteors that have collided with the Earth's crust since it formed. Thus the relative abundances of the heavier elements in our crust will reflect the relative aboundances of heavy elements in the planet(s) from which the meteors were scattered. This in turn should reflect the relative abundances in Earth's core.

Our model also suggests that the Sun and gas giant planets should also have heavy radioactive elements in their inner cores. It is also possible that turbulance in the Sun's core from nuclear fusion obliterates any elemental stratification. While the amount of any heat generated by fission in the Sun will be small compared to the fusion reaction output, fission heating may have played a role in igniting fusion in the Sun long ago and might ignite a fusion reaction in Jupiter or another gas giant in the future.

Conclusion

If radioactive decay were the only source of heat in the Earth's core, we should be seeing a decline in plate tectonic motion and vulcanism. This does not appear to be the case. Therefore, some steady-state heat generation must be at work. Nuclear fission in the Earth's inner core is a viable explanation for observed phenomena.

Future Work

Based on the relative abundances of elements, the approximate mass, size, and composition of the Earth's inner reactive core may be computed. From these numbers, the neutron flux density and fission rate of the reactor can be computed. The calculated heat output can then be be used in an Earth conduction model to match the heat arriving in the mantle with plate tectonic model requirements.

Email Richard dot J dot Wagner at gmail dot com