11.1 Exogenic vs Endogenic Processes

The molding of the landscape at the surface of the Earth is a balance of the exogenic and endogenic processes.

The processes that result from the energy from the Sun are the exogenic or external processes. The processes driven by the energy from within the planet are the endogenic or internal processes.

These are illustrated in section 12.2. of the following figure. On the left are the exogenic processes and the endogenic processes are on the right.

Section 12.1 of this figure illustrates these processes. Above the surface are the exogenic processes. Many of these we have discussed in the first section of the class and they include the hydrologic cycle, the weather and precipitation, and also the currents and waves of the ocean. We will soon discuss the erosion and transport of material by the streams and glaciers. All of these ultimately derive their energy from the Sun.

The internal Earth’s energy drives the motion of the plates – plate tectonics. Because the asthenosphere is plastic, it moves in currents driven by the radioactive decay within the Earth’s core. Molten magma is composed of a variety of minerals and when it reaches the surface they cool in various ways into rock. In addition, the collision of the plates creates relief, the vertical distance of features over the Earth’s surface which includes the mountain ranges and the great trenches of the oceans. The formation of rock is the rock cycle, which we will discuss in this module, and the motion of the plates and creation of relief is the tectonic cycle, which will be the subject of the next module. The balance of the endogenic and exogenic processes that drive the hydrologic, rock, and tectonic cycles are, in total, termed the geologic cycle. Together they explain the formation of the landscape.