Plate Tectonics

The evolution of species on the land is linked to and driven by various climatological and geological changes that operated on the land surface of the earth.

As we will discuss later, the earth currently has significant climate variations on a timescale of 100,000 years. In addition, over the last 200-250 million years the earth is experiencing an era go global tectonic motion which makes the land surface a Dangerous Place to Live:

• Map of recent earthquakes Western USA
• Map of recent earthquakes World
• Map of Current LA Earthquakes

Plate Tectonics means that the crust of the earth is divided into large connected units, all of which are moving relative to one another and colliding with one another in various ways. The idea of Plate Tectonics was first published by the German geologist, Alfred Wegener in 1915 but this theory was largely ridiculed until magnetic mapping of the ocean floor was done in the late 50's. This history of the acceptance of this theory is summarized here .

Summary of Evidence for Plate Tectonics:

• The continents appear that they could fit together like a Jigsaw Puzzle. Just a coincidence?

• Similar fossil records are found in Brazil and North Africa --> could just mean that the climates and hence vegetation and animal life were similar

• Similar rock types are seen in Brazil and North Africa --> this is much harder to explain away especially if the ages of the rock types are similar.

• Sea Floor Spreading --> Magnetic mapping of the ocean floor revealed a history of polarity reversals that formed a mirror image about the Mid-Atlantic Ridge. This indicates that the floor of the Atlantic Ocean is created at the mid Atlantic ridge due to crustal separation. As magma issues forth and solidifies, it records the orientation of the earth's magnetic field at the time of solidification. These newly formed rocks are then carried either East or West of the Mid-Ocean ridge. The floor of the Atlantic Ocean is thus an Age sequence with newly formed rock appearing at the Mid Atlantic Ridge and the oldest rocks being at the North American and European Coastlines. The time of transport from the mid Atlantic ridge to these coastlines is about 210 million years which indicates a total sea floor motion of about 1.5 inches per year.

Now it is recognized that the surface of the earth can be divided up into roughly 10--12 large scale plates and perhaps a number of smaller ones as in the case of the Pacific Northwest

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