ATTERNS AND PROCESSES IN THE PHYSICAL ENVIRONMENT How do we know what is inside the earth?
Our knowledge of the interior of the earth is gained in part from the study of earthquake waves. Rock density can affect the speed at which earthquake waves travel. Some rocks allow these waves to pass quickly, for example granite, others such as shale let thewaves passmore slowly. Earthquakewaves cannot pass through liquids. Analysis of travel paths and travel times for earthquake waves enables geologists
to develop models of the earth’s interior. 1.3 The theory of plate tectonics
Plate tectonics is the study of the processes that cause the movement of the earth’s plates and the landforms that result. The theory of plate tectonics states that the earth’s crust is broken into a dozen or more larger and smaller sections of rock called plates that carry the oceans and continents. The plates are in continual slow motion around the globe. The massive convection currents within the asthenosphere drive this motion. They drag the plates along as they circulate causing them to collide and separate. This is known as the tectonic cycle.
NORTH
JUAN DE FUCA PLATE
AMERICAN PLATE
Equator Equator
PACI F IC PLATE
COCOS PLATE
CARIBBEAN PLATE
SOUTH
NAZCA PLATE
AMERICAN PLATE
SCOTIA PLATE
EURASIAN PLATE
ARABIAN PLATE INDIAN
PLATE
AFRICAN PLATE
INDO-AUSTRALIAN PLATE
PHILIPPINE PLATE
PACIFIC PLATE
ANTARCTIC PLATE Fig. 5 The major crustal plates of the world
The theory of plate tectonics explains why earthquakes, volcanoes, fault lines and fold mountains occur in specific places in the world. The plates collide, separate and slide past each other, all the while destroying, creating and modifying the crust. This is all part of the tectonic cycle.