Plate Tectonics California Standard 3a. & b.

Alfred L. Wegener Alfred Wegener was born in Germany in 1880. He proposed the idea of the continents moving about the surface of the Earth in 1912. This idea was thought foolish at the time. However, he published this idea and after he died in 1930 this idea of the continents moving about became accepted in the 1960’s as more than an idea but a theory.

Alfred Wegener. The father of Plate Tectonics.

The Driving Force Behind Seafloor Spreading Convection, or the heating and cooling of the asthenosphere, below the lithosphere is the driving force behind the movement of the continents. Divergent Plate Boundaries.

Convection Currents

Mid-Atlantic Ridge and seafloor spreading

Evidence 1. Pangaea, original landmass 2.Fossils 3.Climatic changes 4.Rock type and formation

1. Pangaea 1. Wegener proposed that at one time all continents were one which he called Pangaea or “all land”. 2. That these continents drifted to their present location. 3.These continents are continuing to drift. However, he did not propose how they were drifting.

Rodinia the “super” continent

Pangaea

Gondwana and Laurasia second “super” continents.

Plate Boundaries

2. Fossil Evidence The distribution of fossils on different continents helped to support Wegener’s theory of Continental Drift. Some of these fossils were dinosaurs such as Mesosaurus, and plants such as Clossopteris.

Mesosaurus dinosaur fossil and artists concept of animal

Glossopteris fern fossils

Distribution of Fossils

Glossopteris fern

3. Climatic Evidence 1. Presence of warm weather plants on islands a long distance from any warm weather continents. 2. Evidence of glaciers in Africa, India and Australia.

4. Rock Clues 1. Similar rocks on different continents. 2. Same rocks in Eastern U.S. as in Europe 3. Same rocks in S. America as in Africa

Evidence of Plate Movement Volcanoes/earthquakes Paleomagnetism Seafloor spreading

Plate Boundaries Subduction Zone Convergent; subduction zone Divergent boundary

Transform plate Boundaries Transform plate boundaries occur where two plates move past one another. The San Andreas fault that is splitting California apart is just such a plate boundary.

San Andreas Fault

San Andreas fault, aerial view

Tectonic Forces, Uplifting

Continental Divergent Boundary

Africa’s Rift Valley

Convergent Plates The collision of the sub-continent of India smashing into the Eurasian plate creating the tallest mountains chain on Earth the Himalayan mountains.

Indian Plate converging with Eurasian Plate over time Today 55 million years ago Indian Plate converging with Eurasian Plate over time

Tibetan Plateau

San Andreas Fault

Juan De Fuca & N American Plate

Volcanoes and Juan De Fuca

Plate Boundaries

Seafloor Spreading 1. Until the 1950’s scientists did not know very much about the movement of continents. They did not know that the seafloor was spreading apart at the mid-oceanic ridges. 2. In 1960 Harry Hess proposed the concept of sea floor moving or the seafloor being moved apart.

Glomar Challenger Drilling on the Atlantic Ocean, 1968

Seafloor Spreading Evidence 1. The age of the rocks further from the mid-oceanic ridges became greater. 2. Polarity of the rocks indicated that the north and south poles have changed over time, creating magnetic “stripes along the seafloor. This became known as paleomagnetism. .

Paleomagnetism As molten rock solidifies and becomes solid the iron minerals align with the Earth’s magnetic flied. The Earth’s magnetic field has changed from pointing north and south over thousands of years.

Magnetic Clues The Earth’s polarity has changed over the course of millions of years. Therefore, the North Pole has become the South Pole and the South Pole has become the North Pole. Thus, causing the magnetic fields of magnetic rocks to change in ‘stripes’.

When the iron minerals point north this is called normal polarity When the iron minerals point north this is called normal polarity. When they point south this is called reverse polarity. This changing pattern of north and south over thousands of years is called geomagnetic reversal time scale.

Paleomagnetism due to seafloor spreading.

Continental Drift Theory and Dinosaurs

Age of the Dinosaurs relived. http://www.youtube.com/watch?v=bP3JkC0FyMI

San Francisco, 1906

George Strait