Geology

A Layered Earth No physical samples from beneath outermost layer of earth!!!! Clues from: Heat measurements leaking from interior Chemical composition of volcanic gases Chemical composition of volcanic rock Studies of shocks from distant earthquakes Seismic waves

Lithosphere Cool, rigid, ~60 miles thick Asthenosphere Thin, hot flowing ~430 miles thick

A New Age In Geology

Continental Drift Puzzle like fit of continents Even better fit of continental shelves Same fossils on 2 coastlines Coal in Antarctica 1912 Wegener - continental drift Original Land Mass - Pangaea

20th Century Additions to Theory: Earthquakes/volcanoes not random

Dating of seafloor = 200 MYO Continents 3.5-4 BYO Seismic studies suggest molten layer Discovery of Mid Atlantic Ridge

Sea Floor Spreading If new material is being formed it should be hot It is The farther away from the ridge the rock should be younger As it cools and shrinks as it moves away from ridge, it should shrink and increase density It does Sediments should be thicker at edges of oceans than in the middle They are

As earth’s magnetic poles reverse, there should be stripes of rock with minerals pointing to where north was at the time. There is

Plate Tectonics A new name for the 2 old theories - continental drift and seafloor spreading combined Slow!!!!! 2 inches/year in Atlantic 4.8 cubic miles of new seafloor each year

Types of Plate margins 1) Convergent Plates moving together When both rise - mountains When one subducts another - volcanoes

2) Divergent When plates move apart Creates shallow volcanoes mid Atlantic rift and Iceland great examples of this

3) Transform When plates are rubbing side by side Pressure builds and they can ‘lurch” Causes earthquakes San Andreas fault