Lithosphere and Asthenosphere: Facts and Information

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What are the Lithosphere and Asthenosphere

The lithosphere can be defined as the solid outermost surface of a planet. It is the approximately 100 first strong and rocky kilometers of the earth’s surface. Its name is derived from the Greek words for rock, or “litho,” and layer, or “sphere.” When scientists refer to plate tectonics, they are generally referring to the top plate of the earth’s surface, which would be the lithosphere. It is also divided into two sorts of layers- a continental layer and an oceanic layer. These make up accordingly for the land mass and the water on the earth’s surface. The asthenosphere is a weaker layer that flows right underneath the lithosphere. Together, the lithosphere and the asthenosphere comprise what scientists refer to as the earth’s mantle. There are two different kinds of lithosphere which together make up the earth’s surface, or crust. The oceanic lithosphere is essentially what is referred to as the ocean floor. Continental lithosphere is the continental crust, or the formation of earth’s land and continents. It is believed that the oceanic lithosphere is younger than the continental lithosphere. The oceanic lithosphere was made by shifts in Earth’s mantle, whereas the continental lithosphere was shaped by the residue of continuous melting of material.

How Did the Lithosphere and Asthenosphere Form?

Despite much understanding of how the lithosphere and the asthenosphere function and what their roles are in plate tectonics and plate motions, it can only be inferred how they came to be part of Earth’s geology. It is theorized that the continental lithosphere may have come into existence as a result of a process known as melting zones. The two lithospheres – oceanic and continental – are actually formed of two different sorts of material. These various formations may have come about because of different rates of sedimentation and various other geological phenomena, such as metamorphism. Furthermore, oceanic lithosphere may also be created by the bottom of the ocean spreading and causing more material to be brought up to the crust. In other words, Earth’s crust and its atmosphere have been created by the melting and dissolution of Earth’s mantle. The mantle accounts for approximately 80 percent of Earth’s volume and about 70 percent of its mass.

What is the Difference Between the Lithosphere and Asthenosphere?

The asthenosphere differs from the lithosphere mostly because of its composition. Whereas the lithosphere is a rigid structure, the asthenosphere can be described as a heavy liquid flowing beneath it. It is hypothesized that asthenosphere is created as lithosphere is created because it will be dragged about by the various plate motions. The asthenosphere is located about 62 miles beneath the surface of the earth. It has not yet been seen by humans.

Having a clear understanding of both the lithosphere and the asthenospehere has had numerous implications for modern geology and earth science. Many theories of plate motions, the first one having been developed in the 1960s, rest upon knowledge of these parts of the planet’s surface. It is with these theories that scientists, most especially geologists and seismic specialists, are able to predict not only when powerful earthquakes will strike, but also where they will be felt.

It was the British geologist Joseph Barrell who first coined the terms asthenosphere and lithosphere in 1914. He is credited with being the first person to divide the earth into its three main layers: the lithosphere, the asthenosphere and the centrosphere, which is the center, or core, of the planet. Since the asthenosphere was identified as being the less rigid of the layers, Barrell chose a name based on the Greek word for weak, or “asthenis.” Likewise, because the lithosphere is the rocky layer, it is named from the Greek word for rock, “lithos.”

How Would an Earthquake Affect the World’s Lithosphere?

An earthquake can also be defined in terms of the earth’s composition. An earthquake is the movement of the earth that creates a release of energy; it has several definite key elements. These are the focus and the epicenter. The focus is the exact spot on the earth where this movement, or vibration, occurs. The epicenter can be defined as the point on the earth’s surface above the focus. The epicenter, then, could be said to be the spot where the earthquake is most strongly felt on the earth’s surface by those on the earth’s surface.

One may infer that the lithosphere and earthquakes in general are closely related, as an earthquake is essentially created by movements in the earth’s lithosphere. More specifically, the two topics are closely related because of a theory based on earthquake subduction zones. Subduction zones are spots of the earthquake itself where strong and powerful activity is caused by two plates shifting, where one of the earth’s plates subducts beneath the other. Subduction can be defined as the process by which one plate of the earth’s surface shifts so that it moves sideways and beneath a plate located underneath it in the earth’s mantle. Thus, when this shift, or movement of plates happens, an earthquake is felt on the earth’s surface above where this activity is taking place. When this shift happens, the lithosphere is physically altered. A part of it is forced further down, shifting the part of the lithosphere being moved closer to the asthenosphere and the center of the earth itself.

Moreover, there are several types of areas where subduction in the mantle of the earth can occur. These areas are where the plates form a boundary and just as the earth’s surface is varied, these areas are similarly varied, too. If both plates in the lithosphere are meeting under the ocean, this is known as oceanic-to-oceanic convergence. If they are both at the continental level, this is referred to as continental-to-continental convergence. When the plates meet near the coast line, or where the continent meets the ocean, this is called oceanic-to-continental convergence. The place where the plates meet on the lithosphere can be referred to as a fault. There are many well-known faults throughout the earth. One of these is the San Andreas Fault that runs through most of the American state of California.

In other words, the relationship between the lithosphere and an earthquake can be seen as simply a cause and effect of phenomenon. An earthquake, put simply, is a way the earth naturally rids itself of some stress building up within it. Basically, when the earth’s plates shift, stress is put on the lithosphere. If too much stress is put on it and if the lithosphere is too strained or if it cracks, an earthquake will result. This happens when the earth’s actual crust, or the lithosphere, is broken and the energy is released throughout the area as waves under the earth’s surface. Thus, an earthquake happens when the lithosphere snaps under pressure.

Resources About the Lithosphere and Asthenosphere

PDF about Crust and Mantle vs. Lithosphere and Asthenosphere

Images of the Lithosphere and Asthenosphere from windows2universe.org: Brought to you by the National Earth Science Teachers Association

Utah.gov information about the earths layers called the Lithosphere and Asthenosphere

Teacher lesson plans and worksheets for students about the Lithosphere and Asthenosphere including:

Earth: A Unique Planet
In this planet worksheet, students answer questions as they relate to the structure of Earth, energy in the Earth system, continental drift, the theory of plate tectonics, and features associated with plate boundaries.

Space Science: Layers of the Moon
Students identify the lunar layers and construct scale models of them. Using different colors of clay, they create the moon’s core and three layers and cut a triangle into their models to reveal the interior. The lesson concludes with students comparing their models to worksheets.

The World’s Spheres Vocabulary
In this world’s spheres worksheet, students are given nine spheres and they match the given definitions of the sphere with the term.

Heat Up the Floating Plates
Students research the connection between the convection currents within the mantle of the earth and the moving of Earth’s plates. A connection to lessons at previous grade levels on the rock cycle and important background knowledge on rocks is integrated.

Snack Tectonics
Students learn through a hands-on activity how the earth’s tectonic plates interact with each other.

Plate Tectonics Vocabulary
In this plate tectonics worksheet, students match 9 terms with their definitions. Topics include the types of boundaries, the layers of the Earth’s crust, plate tectonics and continental drift.

Theory of Plate Tectonics
In this plate tectonics worksheet, students will review the Earth’s layers that make up the plates, different types of plate boundaries, and the theory of plate tectonics. This worksheet has 5 fill in the blank and 4 short answer questions.

Earth Science II-Earth’s Crust
In this earth’s crust worksheet, students answer 24 questions about the earth’s crust, the atmosphere, plate tectonics and volcanoes. They describe the relationship between plate tectonics and earthquakes and volcanoes. They also diagram heat flow and it’s affects on rock formation on the ocean floor.

Resource by B.Sobey

I am a recent masters graduate from FL. I enjoy the beach, traveling, and writing. I just moved to South Carolina in hopes to find a job as a journalist.

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