Honors 1360 Planet Earth Last time: Leading Up to Plate Tectonics…
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1360 Planet Earth Up to Plate Tectonics… ntain mass balanced by deep buoyancy lid” rock flows on long time scales gsaw Puzzle” fit of continental boundaries eoclimate: Fossils, glacial striae at wrong latitud ilar mountain ranges, rock formations, fossils on either side of the Atlantic tinental Drift: Continents once were one large supercontinent (Pangea) & drifted to current lo an Bathymetry Tectonics Cont’d: A Paradigm Shift 15 September 2008
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15 September 2008. Honors 1360 Planet Earth Last time: Leading Up to Plate Tectonics… Obs : Mountain mass balanced by deep buoyancy Hyp : “Solid” rock flows on long time scales Obs : “Jigsaw Puzzle” fit of continental boundaries Obs : Paleoclimate: Fossils, glacial striae at wrong latitudes - PowerPoint PPT Presentation
Transcript of Honors 1360 Planet Earth Last time: Leading Up to Plate Tectonics…
Honors 1360 Planet EarthLast time:
Leading Up to Plate Tectonics…Obs: Mountain mass balanced by deep buoyancyHyp: “Solid” rock flows on long time scales
Obs: “Jigsaw Puzzle” fit of continental boundariesObs: Paleoclimate: Fossils, glacial striae at wrong latitudesObs: Similar mountain ranges, rock formations, fossils on either side of the AtlanticHyp: Continental Drift: Continents once were one large supercontinent (Pangea) & drifted to current locations
Obs: Ocean BathymetryHyp: ???
Today:• Plate Tectonics Cont’d: A Paradigm Shift
15 September 2008
Earth in the News…
Unusually long “earthquakes” are actually “icequakes” in actively moving glaciers… Greenland icequakes show significantly increasing frequency in the past three summers.
September 2008 “Physics Today”
Then (ca. 1950’s) came the Cold War…
Measured Ocean Bathymetry to facilitate submarine warfare;discovered mid-ocean ridges, trenches, and fracture zones
As part of an ultimately fruitless attempt to use magnetism to search for subs, measured Seafloor Magnetic Lineations
These were found to be Symmetric Across Ridges!
Now Here’s a Puzzle…
To understand, needed two pieces of information fromcontinental studies of rock magnetism:
(1) Rocks acquire the ambient magnetic field directionas they cool through the Curie temperature(called remanant magnetization)
(2) Magnetic dipole direction occasional Reverses
Magnetic Lineations (Symmetric Across Ridges!)
• Magnetite in basalt records field direction when solidified
• Field direction changes!
• Ocean floor slowly moves away from ridges
• “Seafloor Spreading”Testable Predictions?
Age of the Ocean Floor
Drilled/dredged rocks from seafloor and age-dated them!
Question: Why Are There Ridges Where The Ocean IsYoungest?
Wikipedia:
Wikipedia:
WRONG! Never trust a Wiki….Ocean crust is ~ constant 6 km thickness!
Always remember foundations of CRITICAL THINKING: Use multiple sources of information Evaluate the reliability of sources Think about what makes sense!
Recall thermal expansion & thermal
contraction?
HotRock
CoolRock
fast seismic velocity
slow seismic velocity
