Heat, where does it come from

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Transcript Heat, where does it come from

Elastic properties of rocks
Energy – Heat a driver for seismological
Starting with their experiences
What evidence do they have?
Starting with their experiences
Where does this heat come from?
Estimates of the speed
of light from 1870 - 1960
Simplest solution is a story of
Earth’s Age
• Uniformitarianism (Lyell’s Principles of Geology) same geological
processes occurring today have existed throughout geologic time
• Darwin (Origin of Species) estimated that it took 300 million years
to erode a chalk deposit in southern England
• Lord Kelvin - Molten state to solidification via cooling
– temperature at Earth's core = melting point of rocks
– temperature gradient with regard to depth below the surface
(1 degree/50’)
– thermal decrease through conductivity of rocks*
– Estimate of 20 myo to 400 myo)
Challenges to Kelvin’s model
• Assumption of a solid Earth
• 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
Where does the heat come from?
• 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)
Complete the activity
and use your powers
of observation to look
for trends in the data
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
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
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