Big Idea 2: The flow of energy drives the cycling of matter

The Earth is an open system. Energy flows and cycles through the system; matter cycles within it. This cycling is largely driven by the interaction of the differential distribution of solar radiation and internal heat: the constant flow of solar radiation powers much of Earth’s ocean and atmospheric processes on the surface of the system, while the flow of heat from radioactivity within the Earth drives plate tectonics. For example:

One of the fundamental processes known to Earth system scientists is the rock cycle. The rock cycle illustrates the steps involved in the formation of one type of rock from another. It is a system that has operated since the Earth’s origin, and it continues today. The energy that drives weathering and erosion, melting, or an increase in heat or pressure, drives the continuation of the rock cycle.

The landscape we see today in the Northwest Central has been shaped by the geologic forces of the past, and these forces are still active. The movement of Earth’s plates is driven by plate tectonics, illustrating how the flow of energy drives the cycling of matter—the flow of heat from radioactivity within the Earth drives plate tectonics. Evidence throughout the Northwest Central’s terrain tells a story that began billions of years ago with the formation of tectonic plates, and this story continues today. Plate tectonics played a significant role in the formation of the Rocky Mountains when upwelling mantle heat pushed the crust upwards around 68 million years ago. Today, thanks to a swath of fault zones in the Rockies and tectonic activity at the Yellowstone hot spot, the Rocky Mountains and Columbia Plateau regions comprise one of the most seismically active areas in the United States, with as many as 3,000 earthquakes occurring each year.

See Chapter 10: Earth Hazards for more information about seis-mic activity in the Northwest Central.

During the most recent ice age, glaciers advanced and retreated many times throughout the past two million years. One of the great questions in the Earth sciences revolves around the causes of these glacial cycles, with the general consensus pointing toward cyclic variations in the planet’s tilt, movement about its axis, and its orbital shape around the sun. These variations lead to changes in the amount of solar radiation that reaches the Earth, which in turn affect global climate.

The rock cycle, plate tectonics, and the water cycle are all convection-driven. Without convection, Earth would be extraordinarily different.