Elastic properties of rocks Friction/Asperities Energy – Heat a driver for seismological...
Embed Size (px)
Transcript of Elastic properties of rocks Friction/Asperities Energy – Heat a driver for seismological...
Elastic properties of rocksFriction/Asperities
Energy – Heat a driver for seismological processes
What evidence do they have?
Starting with their experiences
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)
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