Look down at your feet. Did you know that you’re standing on a layer of Earth’s geosphere below the floor? The geosphere is the solid or mineral part of Earth. Based on chemical composition, it consists of three layers that have separated through density and temperature. An important part of the TASC Test Assessing Secondary Completion™ Science subtest is understanding the different layers of Earth’s geosphere.
Let’s take a look at each layer, starting from the inside out:
The core consists of two distinct parts: the inner core, made of solid minerals, and the outer core, made of liquid minerals.
The inner core is incredibly hot, almost matching the temperature of the sun’s surface. Despite the high temperatures, this layer is solid due to the immense pressure of the overlying layers (literally, the weight of the world).
The outer core is quite different because of its liquid state, resulting from significantly less pressure. This liquid produces Earth’s magnetic field. The North and South Poles exist because of the outer core’s liquid, even though it's almost 2,000 miles below us.
On top of Earth’s outer core is the mantle. This is the thickest layer of Earth (roughly 1,800 miles thick). The mantle contains mostly iron, like the core, but in the form of silicate rocks. Study.com notes that the mantle moves like a fluid, similar to how Silly Putty® moves. Silly Putty acts like a solid if you poke it hard. If you pull it apart slowly, it acts like a liquid. The ability for rocks to move without breaking is called plasticity.
Like the core, the mantle can be divided into two parts: the upper and lower mantle. The lower mantle is completely solid due to the intense pressure upon it. The upper mantle, also known as the asthenosphere, flows as convection currents. The upper mantle rises as it warms. After it reaches peak temperatures, it cools and begins to sink. The convection cycle is continuous.
The Lithosphere and Crust
The outermost layer of the Earth is called the lithosphere. Only about 60 miles thick, it contains both the crust and a small portion of the upper mantle. This layer is also called the tectonic plates. Broken up into several different pieces, the lithosphere is rigid and does not flow like the asthenosphere. It floats like ice on a lake. Convection currents in the mantle move the plates, causing earthquakes, volcanoes, and mountain range formation.
The crust is extremely thin, breaking relatively easy. Like the other sections, the crust is split into two parts: continental and oceanic.
The thick continental crust is made up of volcanic lava flows, huge granite blocks, and sediments laid down in shallow water or continental seas. Oceanic crust is thin, made of a relatively dense rock called basalt.
As you prepare for the Science subtest, review this visual representation of Earth’s geosphere from Geophysics.edu: