Effects of the Motions of Tectonic Plates Worksheet

University of Phoenix Material                

Effects of the Motions of Tectonic Plates Worksheet

From Visualizing Earth Science, by Merali, Z., and Skinner, B. J, 2009, Hoboken, NJ: Wiley. Copyright 2009 by Wiley. Adapted with permission.

Part 1

This diagram was similar to one Alfred Wegener drew to show the distribution of continents 300 million years ago. His theory of continental drift was met with skepticism in the scientific community.

[pic 1]

1. Describe three forms of evidence Wegener used to support his ideas of continental drift.

1. Wegener found fossils of an ancient tree called the Glossopteris in matching area of South Africa, South America, Australia, India, and Antarctica.  This is consistent with the continents once being joined since it is highly unlikely that they were carried by wind or water from continent to continent (Merali & Skinner,  2009).
2. When the continents are all rotated together the matching shorelines are very similar including the continental shelf which lies just offshore (Merali & Skinner,  2009).
3. When the continents are all rotated together the ages of the rocks generally match as do the location of certain mountain ranges such as the volcanic rock near the joined areas of South America and Africa  (Merali & Skinner,  2009).

1. Years later, the continental drift theory reemerged as plate tectonic theory, with two additional pieces of evidence.

1. In the 1950’s paleomagnetism began to be used as a tool for studying earths history.  This tool is a system of magnetic field recording along side radiometric dating.  Appartently when liquid magma cools into solid rock any iron based minerals in the magma lock in a record of the direction of the earths magnetism including the direction of the poles.  This tool began to be understood later to explain that the continents had drifted apart because material recoverd from different continental areas showed signs of magnetic poles facing different direction during the same time periods.  This gave way to the understanding that since the earth can not have two poles at the same time the continents themselves must have moved and carried the paleomegetized rocks with them  (Merali & Skinner,  2009).
2. In the 1960’s continental drift was further proven by a discovery along the seafloor.  Oceanographers found evidence of seafloor spreading with alternating bands of magnetized volcanic rock along the seafloor traveling along a central ridge. What that means is that if you were able to fold the seafloor together the rocks would line up.  Further study shows that the youngest rock material is near the central ridge where newer magma wells up from below and gets older as you move away from this center.  This is clearer evidence of a split or drift that occurred between land masses  (Merali & Skinner,  2009).

 [pic 3][pic 4][pic 2]

Refer to the images above. Discuss in detail the two pieces of additional evidence that supported Wegener’s theory, now known as the theory of plate tectonics.