AST 248, Lecture 8. James Lattimer. Department of Physics & Astronomy 449 ESS Bldg. Stony Brook University. October 3, 2017

Transcription

1 AST 248, Lecture 8 James Lattimer Department of Physics & Astronomy 449 ESS Bldg. Stony Brook University October 3, 2017 The Search for Intelligent Life in the Universe james.lattimer@stonybrook.edu

2 Oxygenation and the Late Permian Extinction Oxygen generated by aerobic photosynthesis eliminated methane and initiated global cooling.

3 Oxygen Levels at Present Day

4 Seismic (Body) Waves P waves Compressional or longitudinal (sound) waves, can travel through fluid, solid and gaseous materials. P means primary, because they travel faster and arrive sooner. S waves Shear or transverse (analogous to waves on a taut rope), can only travel through solid materials. S means secondary, because they travel less quickly. geophysics.ou.edu/solid earth When a wave hits an interface between two materials of different densities, it can be reflected and/or refracted (bent). Gradual and continuous density changes cause gradual and continuous refraction.

5 P- and S-Wave Propagation geophysics.ou.edu/solid earth liquid solid 140 P-wave shadow zone 104

6 Plate Tectonics Earth s crust is divided into plates. Plates move because they float on the semi-liquid asthenosphere, a region km below the surface at the top of the upper mantle. Energy source is heat conduction from interior. Ritter, Michael E.: The Physical Environment: an Introduction to Physical Geography USGS, Wikipedia

7 Fossil Evidence for Continental Drift 200 Myrs ago

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9 620 Myrs ago

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11 S. Harris

12 Earthquakes Earthquakes caused by slipping of faults when rock cracks. Total energy of earthquakes measured by the Richter Scale. E(MT ) 30 M 6 Global earthquake frequency, as a function of magnitude M, is well-reproduced by the Gutenberg-Richter formula: N( M) 10 8 M per year There are about 1 million earthquakes per year with M > 2. M 10 because rock has a limited strength, M max = 9.5. The total annual energy of all earthquakes is 50,000 MT. The total annual energy of all impactors on the Earth is 1 MT, averaged over the last 100,000,000 years. Most earthquake energy is harmlessly dissipated into the Earth, in contrast to impacts that focus the energy. During the last century, there were 1 million recorded earthquake fatalities, or about 10,000 per year. This is much less than the number of coal-related deaths from mining accidents, black lung, and other diseases.

13 The Richter Scale Magni- Seismic Energy Frequency Example tude (TNT weight) down to M (approximate) Generally not felt, but recorded kg Construction site blast ton 8000 per day Large quarry blast, large WWII bomb tons 1000 per day kton 50,000 per year Small nuclear weapon kton Average tornado kton 6200 per year Slight damage to well-constructed buildings MT 800 per year Double Spring Flat, NV, MT Northridge, CA, 1991 Major earthquake MT 120 per year Largest nuclear weapon MT Landers, CA, 1992 Great earthquake GT 18 per year San Francisco, C, GT Ancorage, AK, GT 1 per year Chile, TT Unknown Fault almost circling Earth PT Earth s total solar energy per year

14 ZooFari, Wikipedia

15 Greenhouse Effect NASA

16 Greenhouse Effect Moon: daily temperature range -175 C (-283 F) to 125 C (257 F) Earth: without atmosphere the global average temperature is -1 C (30 F) Earth: with atmosphere the global average temperature is 15 C (59 F) Greenhouse gases include H 2 O (36-70%), CO 2 (9-26%), CH 4 (4-9%), O 3 (3-7%) Greenhouse effect on Venus: +250 C Pieter Tans

17 Carbon Cycle NASA Earth Science Enterprise

18 Preservation of Atmosphere Atmosphere can be lost thermal escape giant impacts solar wind e.g. Mars Requirements for planetary magnetic field abundant Fe molten interior convection rapid rotation

19 Long-Term Climatic Change The carbon cycle is a thermostat, but is not always stable, it can be driven to instability This leads to periods of intense glaciation, called snowball earths, when ice sheets covered virtually the entire planet, followed by hothouse earths, involving intense periods of heat Hothouse earths accompanied by dramatic growth in magnitude and diversity of life (speculation about development of eucaryotes and multicellular animals) Major snowball earths identified: 2.2 Gyr ago (Makganyene), perhaps connected with removal of methane, a powerful greenhouse gas, from early Earth atmosphere 710 Myr ago (Sturtian) 635 Myr ago (Marinoan), immediately precedes Cambrian explosion

20 Evidence global glacial deposits Cap carbonate rocks, indicating anomolous ocean chemistry increased C 13 /C 12 ratios consistent with deep freezes that killed off most of photosynthetic life in water banded iron formations indicating anoxia in oceans ca. 650 Myr ago glacial deposits W. T. Hyde, T. J. Crowley, S. K. Baum a

21 Snowball Earth

22 atropos.as.arizona.edu/aiz/teaching/a204

23 Major Extinctions