What is the Difference Between the Asthenosphere and the Lithosphere?

The lithosphere and asthenosphere are both mechanical layers of the Earth. The layers of the Earth can be organized by composition (what they are made of) or mechanical properties (how they move). The lithosphere is made up of the crust and the top of the mantle. The asthenosphere is the layer within the mantle below the lithosphere.

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What is the Lithosphere?

The lithosphere makes up all of the hard, solid rock on Earth. While solid rock exists in the asthenosphere, the layer below the lithosphere, it is soft, not hard. It is the slow movement of soft rock within the asthenosphere that drives the movement of the tectonic plates that make up the lithosphere.

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The lithosphere is made up of the crust and the top layer of the mantle. It is broken up into tectonic plates that fit together like puzzle pieces along the Earth’s surface. The plates are always moving because of convection currents within the asthenosphere. In these convection currents, hot rock from the bottom of the asthenosphere expands and rises to the top. When the rock cools, it contracts and falls back down to the bottom, and is heated again. The solid rock flows very slowly, about as fast as your fingernails grow.

Recycling the Lithosphere

New rock is added to the lithosphere when magma cools and forms igneous rocks. This happens when volcanoes erupt and at the Mid-Ocean Ridge deep under the ocean. When new rock is added to the tectonic plates on either side of the Mid-Ocean Ridge, the other side of the plate is forced down into the mantle at subduction zones. As a result, the oceanic crust of the lithosphere is continually being recycled. The oldest oceanic crust found on Earth is about 200 million years old. Meanwhile, the oldest continental crust is nearly four billion years old.

Oceanic Crust and Continental Crust

Oceanic crust and continental crust are also made up of different types of igneous rock. Continental crust is primarily granite, and oceanic crust is mainly basalt. Basalt is denser than granite. As a result, oceanic crust always subducts under continental crust.

Plate Boundaries

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There are three types of plate boundaries to describe how tectonic plates of the lithosphere interact. First, at a convergent boundary two plates collide. If one of the plates is denser than the other, it will subduct into the mantle. When two continental plates collide, they push each other up and form mountains, like the Himalayas. Second, at a divergent boundary, two plates move away from each other. The Mid-Ocean Ridge is an example of a divergent plate boundary. Finally, a transform boundary occurs when two plates are sliding past each other. The San Andreas Fault formed as a result of the Pacific North American plate’s transform boundary.

How the Lithosphere Changes

The lithosphere also changes through weathering, erosion, and deposition. Wind, water, animals, and plants break rocks into smaller pieces called sediments. These sediments are carried to new places by wind and water in a process called erosion. Deposition happens when the sediments settle in a new place.

The rock cycle describes how the rocks of the lithosphere change. Igneous rocks form when magma cools, sedimentary rocks form from layers of sediments, and metamorphic rocks form in intense heat and pressure. Each type of rock can become the other types of rock under the right circumstances.

What is the Asthenosphere?

The asthenosphere is one of the mechanical layers of the Earth. It rests between the lithosphere and the mesosphere within the mantle. The asthenosphere is made up of soft, solid rock similar to silly putty. The rock is soft enough to flow, but it only moves about as fast as your fingernails grow.

Within the Earth, temperature increases as you travel closer to the core, so the bottom of the asthenosphere is hotter than the top of the asthenosphere. Hot rock at the bottom of the asthenosphere expands and rises. At the top of the asthenosphere, the rock cools and contracts, falling back down where it is heated and rises again. This movement forms convection currents similar to the convection currents seen in a pot of boiling water.

How the Asthenosphere and the Lithosphere Connect

The convection currents within the asthenosphere move the tectonic plates that make up the lithosphere around the Earth.

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Below the asthenosphere, the mesosphere is another part of the mantle. The rock of the mesosphere is harder than the rock in the asthenosphere, so it doesn’t flow as easily. The mesosphere is also hotter than the asthenosphere because it is closer to the center of the Earth. Occasionally, rock from the asthenosphere will enter the mesosphere, but this doesn’t happen often.

Compositional Layers of the Earth

You can teach your students about the compositional layers of the Earth with this reading passage. Click on the picture to find it at Teachers Pay Teachers.

Mechanical Layers of the Earth

You can teach your students about the mechanical layers of the Earth with this reading passage. Click on the picture to check it out at Teachers Pay Teachers.

Helping Students Remember What They Learn

Once students have learned and processed the information about the layers of the Earth, it is time to strengthen their new neural connections. Neurons that fire together wire together, and we want our students’ brains wired to remember what they learned. The best way to achieve this is repeated practice.

You can require repeated practice in your classroom by having quick quizzes at the beginning or end of each class period. Ask students about topics they learned about over the past few days. Being forced to remember the information will make it easier for them to remember the information later. You don’t have to grade or even collect these quizzes. The act of trying to answer the questions and hearing the right answers will build your students’ neural networks around the layers of the Earth.

You can also encourage your students to study with flashcards. Toward the end of each unit, give your students flashcards that review all of the main information they learned. Give them time in class to practice with the flashcards in class and assign flashcard practice as homework. Just a few minutes of practice a day will make a huge difference in how much they remember about the layers of the Earth for the final test. This might be the most helpful part of your lesson plans because your students will see the benefits of flashcards and hopefully start using them as a tool in other classes.

The Geosphere

Middle School Science

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