Читать книгу Geology For Dummies - Alecia M. Spooner - Страница 19

For many decades, earth scientists studied different parts of the earth without knowing how all the features and processes they examined were tied together. The idea of plate movements came up early in the study of geology, but it took a while for all the persuasive evidence to be collected, as I describe in Chapter 8.

By the middle of the twentieth century, scientists had discovered the Mid-Atlantic Ridge and gathered information about the age of sea floor rocks across the ridge. With this evidence they proposed the theory of plate tectonics suggesting the earth’s crust is broken into pieces, or plates. Where two plates touch and interact is called a plate boundary.

Exactly how the earth’s crustal plates interact is determined by the type of motion and type of crustal material. These interactions are described as plate boundary types and include:

 Convergent boundaries: At convergent boundaries, two crustal plates are moving toward one another and come together. Depending on the density of the crustal plates, this collision builds mountains, or causes plate subduction (meaning one plate goes beneath another), producing volcanoes.

 Divergent boundaries: At divergent plate boundaries, two crustal plates are separating or moving apart from one another. These boundaries are most commonly observed along the sea floor, where the upwelling of magma along the boundary creates a mid-ocean ridge, but they may also occur on continents, such as in the African rift valley.

 Transform boundaries: At transform boundaries, the two plates are neither colliding nor separating; they are simply sliding alongside one another.

In Chapter 9, I provide the details on the different characteristics of continental plates and how they interact as they move around Earth’s surface, including the particular geologic features associated with each plate boundary type.