Exploring Our Fluid Earth

Moving Continents and Plate Tectonics

 

According to the Law of Superposition, layers of rock are deposited in order of time, with the oldest layers on the bottom and the youngest layers on top. However, in the 1880s, scientists observed rock layers that did not seem to fit the Law of Superposition. Geologists observed older rock layers on top of younger layers. Scientists studying these formations believed they were due to what geologists called thrust faults, which are areas where one large layer of the earth is pushed up on top of another. At the time, the idea that the Earth’s crust moves vertically, geosynclinal theory, was widely accepted and believed to be the cause of the thrust faults.

 

Today, the scientific explanation for thrust faults and other natural phenomena, such as earthquakes, is plate tectonics. The theory of plate tectonics is the currently accepted model of large-scale movement of the Earth’s crust and upper mantle, the lithosphere. The plate tectonics model explains how major and minor plates of the lithosphere move relative to each other at plate boundaries. Evidence for plate tectonics is plentiful. Supporting evidence, based on decades of research, includes:

 

 

Although scientific evidence supports plate tectonics, in 2008, over 20% of Americans incorrectly answered a question that asked if continents had been moving for millions of years and if continents would continue to move*. It is unclear whether those who got the question wrong did not understand the principles of plate tectonics or believe that the earth is much younger than scientific evidence suggests.