Chapter 2

Through your investigations, you will explore the large-scale forces that change the geosphere. Investigating why volcanoes form, what makes some regions have more earthquakes than others, why earthquakes and volcanoes often happen together, or how mountain systems form, is a search for explanations. Earth's systems work because both matter and energy move into and out of the systems.

You will explore the parts of the geosphere, from core to crust. You will learn how to use models to study things that you cannot directly observe, whether it is the inside of the Earth, or how seismic waves move through solid rock. You will learn about the heat energy inside the Earth and how this heat makes mantle rock and magma rise and sink. Energy is transferred as stress builds up in rock and is released as seismic waves in an earthquake, or as the heat of friction when rocks move along a fault.

The geosphere changes on timescales that range from seconds to hundreds of millions of years. This can include the incredibly slow churning of mantle rock in a convection cell; the forces that shove blocks of the Earth's crust skyward into mountains; as well as the 15 seconds of shaking that destroyed thousands of buildings in the Loma Prieta earthquake. Each of these processes, forces, and events shares a common explanation through the theory of plate tectonics. The seafloor spreading hypothesis, advanced more than 40 years after Alfred Wegener had proposed continental drift, was a key turning point in our search of an explanation for earthquakes, volcanoes, and mountain building.