4_Marine_Geology_2 - Marine Geology Geomagnetic Reversals 1...

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1 Marine Geology 1. Present geomagnetic intensity is 35% lower than the high value achieved approximately 2000 years ago. 2. There has been a 10–15% decline over the last 150 years and this has accelerated in the past several years 3. If rates continue, the dipole will collapse by about 3000–4000 AD. Further Reading… ht p:/ www.psc.edu/science/glatzmaier.html ht p:/ en.wikipedia.org/wiki/Geomagnetic_reversal ht p:/ www.newscientist.com/article/dn4865.html 1. The Earth's magnetic Feld takes an average of 7000 years to reverse its polarity 2. The Earth's magnetic north pole is drifting from northern Canada towards Siberia at an accelerating rate a) At the beginning of the 20th century: About 10km per year b) In 2003: up to 40km per year 1. Some speculate that a greatly diminished magnetic Feld during a reversal period will expose the surface of the earth to potentially damaging increase in cosmic radiation. 2. However, humans and their ancestors, have certainly survived many previous reversals and there is no uncontested evidence that a magnetic Feld reversal has ever caused any biological extinctions. Geomagnetic Reversals… Outline Last ±riday… 1. Basic Morphology of the Seafloor 2. Plate Tectonics Theory Development a) supporting evidence/observations b) formulation of the tectonic concept Today (Monday)… 1. details of plate boundaries a) divergent b) convergent c) transform 2. Mantle Hot Spots 3. Passive and Active Contiental Margins 4. Summary
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2 Tectonic Plate Divergence, Spreading and Convergence Convection in the Mantle – hot molten rock rises to the surface at divergent boundaries,
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This note was uploaded on 09/28/2008 for the course EAS 1540 taught by Professor Monger during the Fall '07 term at Cornell.

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4_Marine_Geology_2 - Marine Geology Geomagnetic Reversals 1...

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