Heat in our Earth System

Starting with their experiences

Evidence against this model

Earth’s Age• Charles Lyell's Principles of Geology. Uniformitarianism, which

held that the same geological processes occurring today have existed largely in their present state throughout all of geologic time.

• Darwin, Origin of Species, estimated that it took 300 million years to erode a chalk deposit in southern England

• Kelvin - Molten state to solidification and cooling– temperature at Earth's core, – temperature gradient with regard to depth below the

surface (1 degree/50’)– thermal conductivity of rocks– (20 myo to 400 myo)

Challenges to Kelvin’s model• Underlying data. • Assumption of a solid Earth. • Arrogance and speculative findings • T.C. Chamberlain– Argued that the Earth had never been a molten sphere;

rather Earth had formed from the slow accumulation of solid material like asteroids.

– Attacked Kelvin's assumption about a closed system of dwindling initial heat

– Offering the possibility that the then-unknown internal structure of atoms could contain massive amounts of potential energy

Complete the activity and use your powers of

observation to look for trends in the

data

Earth’s Internal Heat

• 20% Residual heat from accretion and gravitational collapse

• 80% Radioactive decay– Uranium-238 (4.47 × 109)

– Uranium-235 (7.04 × 108)

– Thorium-232 (1.40 × 1010) – Potassium-40 (1.25 × 109)

Earth’s Energy Budget

• Solar Radiation - (99.978%, or nearly 174 petawatts; or about 340 W m-2)

• Geothermal Energy - (0.013%, or about 23 terawatts; or about 0.045 W m-2)

• Tidal Energy – (0.002%, or about 3 terawatts; or about 0.0059 W m-2).

• Waste Heat - (about 0.007%, or about 13 terawatts; or about 0.025 W m-2)

Average 25oC/km

Tufts.edu

What is the parent material?

What is the daughter material or the decay product of the parent

material

What is a half-life?

When a radioactive isotope decays, it creates a decay product. By comparing the number of parent and daughter atoms in a sample, we can estimate the amount of time since the sample was created.

The amount of time it takes for half of an parent isotope to turn into its daughter isotope is called the half-life.

Some configurations of the particles in a nucleus have the property that, should they shift ever so slightly, the particles could fall into a lower-energy arrangement.

One might draw an analogy with a tower of sand: while friction between the sand grains can support the tower's weight, a disturbance will unleash the force of gravity and the tower will collapse.Such a collapse (a decay event) requires a certain activation energy.

In the case of the tower of sand, this energy must come from outside the system, in the form of a gentle prod or swift kick.

In the case of an atomic nucleus, it is already present. Quantum-mechanical particles are never at rest; they are in continuous random motion. Thus, if its constituent particles move in concert, the nucleus can spontaneously destabilize.

As a radioactive isotope decays, particles are ejected from its nucleus for the purpose of

stabilizing the atom. Radioactive decay processes produce

electromagnetic radiation (gamma rays, for example)which transmit energy from the nucleus to the environment. Additionally, the

ejected particles have kinetic energy that ultimately converts to thermal

energy as the particles are mechanically resisted by their

environment.