The Geosphere: deep into the earth

September 24, 2022

Written by: Caroline Kim

Recently, we discussed the atmospheric layers of the earth, and this week we’ll discuss the structure of earth. Earth’s structural layers make up landscapes, which have relevance to all wildlife and humans. The layers proceed as follows from outer to inner: the crust, mantle, outer core, and inner core. The crust and top part of the mantle is considered part of the lithosphere, while the rest of the mantle is considered what is known as the asthenosphere. The center (cores) is known as the geosphere.

The first layer, the crust, reaches 25 miles below the ground from the surface. Consisting of mostly solid rocks and minerals, the “dynamic geology of earth’s crust is formed by plate tectonics” (Crust). This idea of plate tectonics essentially is the idea of continental drift, in which the plates of earth’s outer shell glide over the inner shells, which are malleable (Means). The depth, isostasy (forces the allow movement of the layers), and temperature all vary with the crust. In terms of temperature, the top of the crust can be similar to the climate of the region, but deeper down, temperatures can reach from 392- 752 degrees Fahrenheit (Crust). Though including igneous, metamorphic, and sedimentary rocks, most of the crust is igneous. This seems logical, considering igneous rocks formed from cooled lava/magma, while sedimentary rocks are from accumulation of particles, and metamorphic rocks pressure/heat/chemicals (Three Types of Rock: Igneous, Sedimentary & Metamorphic: AMNH).

The next layer, 1802 miles thick and comprising 84% of earth's volume, is the mantle (Mantle). The mantle was formed from molten material and the process of outgassing where “Water trapped inside minerals erupted with lava” (Mantle). This layer consists of silicates, magnesium oxide, iron, etc. (Mantle). Temperatures in this layer range from 1832-6692 degrees Fahrenheit (increasing temperatures closer to the core); likewise, geothermal gradients (heat and pressure measurement) also increase as you near the core; however, due to mantle convection (transfer of heat to the lithosphere), the overall layer cools over time (Mantle). Due to these factors, this layer of the asthenosphere is much more malleable than the lithosphere. Another important aspect of this layer to take note of is the transition zone (255-410 miles below earth’s surface); here, the rocks’ crystalline structures adapt to become much more compact (Mantle). Surprisingly, this layer also happens to contain as much water as the oceans on earth’s surface: it exists in the form of hydroxide, which are trapped in the rocks’ structures (Mantle). Counterintuitively, the lower mantle (warmer) is actually much less ductile than the upper mantle (Mantle).

Deep at the center of our planet is the sphere we call the earth’s core: hot, dense, 1802 miles below the surface, and has a radius of 2165 miles, and consists of mostly iron/nickel (Core). The outer core ranges in temperature from about 8,132- 9,932 degrees Fahrenheit and is quite malleable; this is where convection occurs, creating earth’s magnetic field (Core). On the other hand, the inner core’s temperature is approximately 9,392° Fahrenheit and has too great a density to be malleable (Core). This unique inner core doesn’t rotate in sync with the rest of earth, slightly different in direction and speed (Core).

Understanding the function of earth’s geosphere is important for society in terms of energy, mineral, and water resources as well as infrastructure development (Benefits of Understanding the Earth at Its Core: U.S. Geological Survey).

Sources:

“Earth Structure.” National Geographic Society, https://education.nationalgeographic.org/resource/resource-library-earth-structure.

“Crust.” Edited by Jeannie Evers, National Geographic Society, https://education.nationalgeographic.org/resource/crust.

Means, Tiffany. “What Is Plate Tectonics?” LiveScience, Purch, 13 May 2022, https://www.livescience.com/37706-what-is-plate-tectonics.html.

“Three Types of Rock: Igneous, Sedimentary & Metamorphic: AMNH.” American Museum of Natural History, https://www.amnh.org/exhibitions/permanent/planet-earth/how-do-we-read-the-rocks/three-types.

“Mantle.” Edited by Jeannie Evers, National Geographic Society, https://education.nationalgeographic.org/resource/mantle.

“Core.” Edited by Jeannie Evers, National Geographic Society, https://education.nationalgeographic.org/resource/core.

“Benefits of Understanding the Earth at Its Core: U.S. Geological Survey.” Benefits of Understanding the Earth at Its Core | U.S. Geological Survey, https://www.usgs.gov/news/featured-story/benefits-understanding-earth-its-core.