There are seven major plates and several smaller ones. As these plates move, they collide with, separate from, or slide past each other along their boundaries. It is along these plate boundaries that nearly all earthquakes, fold mountains and volcanoes occur. Plate tectonics explains how and why this movement occurs.
As these plates move, they interact with each other, greatly shaping our planet. Theories
The theory of plate tectonics was formed as a result of evidence from several earlier theories:
• The theory of continental drift – Alfred Wegner (1912) • The theory of convection currents – Arthur Holmes (1928) • The theory of mid-ocean ridges – Maurice ‘Doc’ Ewing (1947) • The theory of seafloor spreading – Harry Hess (1962)
These theories served as building blocks of information. They combined to make up the theory of plate tectonics.
The Earth’s plates move at roughly 1 cm per year (roughly the same speed as human fingernails grow!). However some plates move faster at up to 4 cm per year.
Eurasian Plate
North American Plate
Arabian Plate
Pacific Plate African Plate
Nazca Plate
South American Plate
Indo-Australian Plate
Philippine Plate
Pacific Plate
Antarctic Plate
: Fig. 1.5 The Earth’s crust is broken into sections called plates. Continental Drift
Alfred Wegner was a German meteorologist. He developed the theory of continental drift, which states that the world’s continents are constantly moving. This theory provided the foundations of what was eventually to become the theory of plate tectonics.
) Fig. 1.6 Alfred Wegner
PATTERNS AND PROCESSES IN THE PHYSICAL ENVIRONMENT 9 GEO DICTIONARY
Meteorologist: a scientist who studies atmospheric conditions and weather patterns
Familiarise yourself with a map of the world. Make sure you can identify the following:
Note!
• All continents • All major oceans • Iceland
In Chapter 2, we will look at plate boundaries and how they interact with each other in more detail.
