Plate Tectonics: The Modern Update to Continental Drift
Plate tectonics is the modern update to the idea of continental drift, which had been proposed by Alfred Wegener in 1912. This theory, first developed in the 1950s and 1970s, explains how the continents move around Earth's surface and how it can be shaped over geologic time.
The Lithosphere and the Movement of Plates
The outer layer of the Earth, called the lithosphere, is broken into a jigsaw puzzle of large and small plates -- slabs of rock with both continents and seafloor that slide atop a hot, slowly swirling inner layer. Moving at rates of 2 to 10 centimeters per year, some plates collide, some diverge and some grind past one another.
Formation of New Seafloor and Volcanoes
Some of these movements create new seafloor along submarine mountain ranges called spreading ridges and can form chains of volcanoes. Others push against each other and subduct, or slide beneath, one another to form a deep trench that is drawn into the Earth's mantle, where magma rises and volcanoes grow.
Locations and Effects of Plate Movements
These motions occur at many locations on Earth, including ocean ridges, subduction zones and transform faults. They produce earthquakes, mountains, and the uplift and sinking of land. Throughout the world's oceans, Earth's tectonic plates are bounded by mid-ocean ridges and subduction zones (partly collisional boundaries), as well as transform faults. The motion of these boundaries is the basis for the movement of the lithosphere, which forms a mosaic of plates ranging in thickness from 50 to more than 200 km thick.
The Role of Plate Tectonics in Shaping Earth's Surface
The motions of these plates cause rifting and uplift, but also make the Earth's surface look the way it does today. This enables geoscientists to track Earth's history, and understand how Earth has changed over time. There are 15 to 20 major and minor plates on Earth, depending on how they're defined. These include the North American, South American and Pacific plates as well as dozens of smaller ones. Most scientists think plate tectonics took over from earlier planetary development about 3 billion years ago, based on ancient magmas and minerals preserved in rocks from that period. However, researchers have found evidence that the process could have been active for as long as 4 billion years.
Driving Forces and Satellite Data
A major driving force of plate motion is the weight of cold, dense oceanic plates that sink into deep rifts in the Earth's mantle. Other forces, such as "slab pull," are thought to be responsible for a smaller percentage of the motion. Increasingly, scientists are using satellite data to determine the motion of the planet's plates and are able to calculate plate margins more accurately than ever before. But there's still a lot to learn about the role that plate tectonics plays in forming the Earth's crust and interior.
Interactions Among Earth's Plates
There are three main types of interactions among the plates on Earth, namely divergent boundaries where continents drift apart and mountains form, convergent boundaries where two continents collide and volcanic arcs form, and transform boundaries where the plates grind past one another and strike-slip faults create. In each case, these plate-based interactions can cause earthquakes, uplift and sinking of land, and formation of new ocean floor.
