Plate Tectonics and Volcanoes Edu 370 – Earth Science

Evidence for the Theory of Plate Tectonics In 1912 Alfred Wegener, a scientist, found evidence to support his “Continental Drift Theory” now known as Plate Tectonics. What conclusions can you draw? Maps Fossils – similar fossils from the late Paleozoic age (~250 million years ago) found on the edges coasts of present day Africa and South America

Evidence for the Theory of Plate Tectonics Rock belts found on the western edge of Africa match rock belts found on the eastern edge of South America, suggesting the that the two were once one large land mass that was ripped apart Glacier striations match on the edge of South America and Africa. Glaciers covering both continents left behind material (striations) when they melted and receded. The striations suggest that the glacier receded from Africa to South America – this could only be true if the Atlantic Ocean were not between the two continents

Evidence for the Theory of Plate Tectonics Coal deposits found in present day Antarctica and Pennsylvania were found to be fossils of tropical animals. Why? Because modern day Antarctica and North America were closer together 250 million years ago The theory, however, was mostly rejected until the 1950-1960’s which was when seismologists finally had the technology to provide more evidence proving the theory to be correct

The Theory of Plate Tectonics Plate Tectonics is the theory that describes the earth’s outer layer being made up of a layer of “plates” that float on the asthenosphere. As a result of the plates floating on the more fluid asthenosphere, there is a pattern of drift between the continents; the plates are moving between 1-10 cm/year Plate Tectonic Theory can explain the existence of earthquakes, volcanoes, mountain ranges as well as oceanic trenches

Two Types of Crust Continental Crust – 20-80 km in depth and about 3 billion years old; made up of granite (Landmass) Oceanic Crust – 10 km in depth and anywhere from 70-100 million years old; made up of basalt; thinner but denser (Under oceans) Underneath these two crusts is the upper mantle, which is more rigid; beneath this is the asthenosphere which is thought to be more liquid and fluid and cause the plates to move and drift

Three Types of Plate Movement: Divergent Plate Movement When two oceanic plates move apart, the plates are said to be divergent This type of movement explains “sea floor spreading” and the continual regeneration of new ocean floor along a ridge At the site of plate divergence, magma rises up from the mantle and new sea floor is formed (which explains why the ocean crust is only 70-100 million years old vs. continental crust which is 300 billion years old)

Three Types of Plate Movement: Convergent Convergence occurs when two plates collide together; the collision causes the plates to become smaller The site of collision is called a convergent plate boundary If oceanic crust and continental crust collide, the oceanic crust, which is thinner and denser “slides” underneath the thicker, lighter continental crust, causing volcanoes If two oceanic plates collide, one will slide under the other, causing volcanoes once again This type of movement, where one plate slides under another, is called subduction

Three Types of Plate Movement: Convergent (cont’d) When two continental plates collide, mountains are formed from the resulting impact, pushing land upward – sometimes these collisions also cause magma to be released from the asthenosphere which result in more volcanoes

Three Types of Plate Movement: Transform Plate Boundaries When two plates move laterally against each other, the resulting friction and pressure between the two erupts in an earthquake.

Locations of Volcanoes and Earthquakes around the Earth A map of volcanoes and earthquakes seems to prove the that the three types of movement, as well as the existence of the plates, really does cause these phenomena The “Ring of Fire” in the Pacific Ocean outlines where the Pacific Plate and Philippine Plate Collide and cause many, many volcanoes

Names of the Different Plates The plates are: Eurasian plate, Australian-Indian plate, Philippine plate, Pacific plate, Juan de Fuca plate, Nazca plate, Cocos plate, North American plate, Caribbean plate, South American plate, African plate, Arabian plate, the Antarctic plate, and the Scotia plate.

Acknowledgements http://volcano.und.nodak.edu/vwdocs/vwlessons/plate_tectonics/introduction.html http://www.enchantedlearning.com/subjects/astronomy/planets/earth/Continents.shtml http://pubs.usgs.gov/publications/text/understanding.html#anchor19173262