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AST 248, Lecture 8
James Lattimer
Department of Physics & Astronomy449 ESS Bldg.
Stony Brook University
February 24, 2020
The Search for Intelligent Life in the [email protected]
James Lattimer AST 248, Lecture 8
Oxygenation and the Late Permian Extinction
Oxygen generated byaerobic photosynthesiseliminated methane andinitiated global cooling.
James Lattimer AST 248, Lecture 8
O2, CH4 Levels
Huang et al. (2018)
20.95% -
20.83% -
James Lattimer AST 248, Lecture 8
Seismic (Body) WavesI P waves – Compressional or longitudinal (sound) waves, can
travel through fluid, solid and gaseous materials. P meansprimary, because they travel faster and arrive sooner.
I S waves – Shear or transverse (analogous to waves on a tautrope), can only travel through solid materials. S meanssecondary, because they travel less quickly.
When a wave hits an interface betweentwo materials of different densities, itcan be reflected and/or refracted (bent).
Gradual and continuous density changescause gradual and continuous refraction.
geophysics.ou.edu/solid−earth
James Lattimer AST 248, Lecture 8
P- and S-Wave Propagation
geophysics.ou.edu/solid−earth
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ave
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104◦
140◦
solid
liquid
James Lattimer AST 248, Lecture 8
Plate Tectonics
Earth’s crust is divided into plates.Plates move because they float onthe semi-liquid asthenosphere, aregion 100–250 km below the surfaceat the top of the upper mantle.Energy source is heat conductionfrom interior.
USGS, Wikipedia
Ritter, Michael E.: The Physical Environment:an Introduction to Physical Geography
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James Lattimer AST 248, Lecture 8
Fossil Evidence for Continental Drift
200 Myrs ago
James Lattimer AST 248, Lecture 8
James Lattimer AST 248, Lecture 8
620 Myrs ago
James Lattimer AST 248, Lecture 8
James Lattimer AST 248, Lecture 8
S. Harris
James Lattimer AST 248, Lecture 8
EarthquakesI Earthquakes caused by slipping of faults when rock cracks.I Total energy of earthquakes measured by the Richter Scale.
E (MT ) ≈ 30M−6
I Global earthquake frequency, as a function of magnitude M,is well-reproduced by the Gutenberg-Richter formula:
N(≥ M) ≈ 108−M per year
I There are about 1 million earthquakes per year with M > 2.I M ≤ 10 because rock has a limited strength, Mmax = 9.5.I The total annual energy of all earthquakes is 50,000 MT.I The total annual energy of all impactors on the Earth is 1
MT, averaged over the last 100,000,000 years.I Most earthquake energy is harmlessly dissipated into the
Earth, in contrast to impacts that focus the energy.I During the last century, there were 1 million recorded
earthquake fatalities, or about 10,000 per year. This is muchless than the number of coal-related deaths from miningaccidents, black lung, and other diseases.
James Lattimer AST 248, Lecture 8
The Richter Scale
Magni- Seismic Energy Frequency Exampletude (TNT weight) down to M (approximate)
Generally not felt, but recorded1.0 32 kg Construction site blast2.0 1 ton 8000 per day Large quarry blast, large WWII bomb3.0 30 tons 1000 per day4.0 1 kton 50,000 per year Small nuclear weapon4.5 6 kton Average tornado5.0 30 kton 6200 per year
Slight damage to well-constructed buildings6.0 1 MT 800 per year Double Spring Flat, NV, 19916.5 6 MT Northridge, CA, 1991
Major earthquake7.0 30 MT 120 per year Largest nuclear weapon7.5 180 MT Landers, CA, 1992
Great earthquake8.0 1 GT 18 per year San Francisco, C, 19068.5 6 GT Ancorage, AK, 19619.0 30 GT 1 per year Chile, 196010.0 1 TT Unknown Fault almost circling Earth12.0 1 PT Earth’s total solar energy per year
James Lattimer AST 248, Lecture 8