Continental Drift

 The earth is composed of several layers that go through several changes that are driven by processes within the earth. These processes occur because of heat and density.

Albert Wegner  German Scientist that came up with the hypothesis of continental drift in  He observed several maps and came up with a question that he proposed a hypothesis from.  Take a look at the map and discuss with your partner when he may have questioned in 1912.

Map of the world Use map on Page 240 with Pangaea Activity

Wegner’s Hypothesis  He hypothesized that there was once one super continent  250 million years ago  The crumpling of crust created the mountain ranges

Evidence  Not only did the continents look as if they fit together, but there should be some sort of fossil and rock evidence that they once were connected.  Explain how studying fossils and rock formations on different continents prove their was a super continent?  Mesosaurus, Climate & Rock Formations

Mid-Oceanic Ridges  Undersea mountain ranges through the center of which run steep, narrow valleys.  Magma runs up through the lithosphere and out of these ranges into the ocean floor.

Oceanic Floor Spreading  The sediment is thinner the closer it gets to the narrow valley the magma comes out of  They dated the fossils that were found near the oceanic ridges and found out that the fossils are younger the closer you got to the ridge.  This could only suggest what?  The rocks in the ocean are younger that the rocks found on the surface. The surface rocks are 3.8 bya while the ones under ground were never older than 175 myo.

Harry Hess  1950’s he through that the rift at the top of the ridge was where magma rises to fill the crack and as the rock moves away from the rift new magma replaces the empty spot.

Hess’ Hypothesis  His hypothesis was that if the seafloor was moving it might drive the moving of the continents too.  Convection Currents & Pie Pan activity

Paleomagnetism  Earth’s Polarity Earth’s Polarity Earth’s Polarity  In the 1960’s paleomagnetism –the study of the magnetic properties of rock would give the final evidence of continental drift  Paleomagnetism-study of the alignment of magnetic minerals in rock as it is formed.  As rocks form the iron-rich minerals within them will align with the magnetic field of the earth. This becomes permanent and may not be today’s magnetic field

 Iron Filling  Scientists were able to map the reversal of magnetic fields on the ocean floor and found that each side of the ridge mirrored the other  They were able to date these rocks with ones on land with similar magnetic fields and found that younger rock was at the center and older was farther away.  Did this support Hess’ Hypothesis?

Theory of Sea-floor Spreading  Molten rock from the rift valley’s cools and hardens and then is carried like a conveyer belt away so that new rock can be formed on the surface of the ocean.  Long after his death Wegener’s Continental Drift theory was accepted.