The Earth’s Layers

What are the major layers of the Earth?

The Earth is generally divided into four major layers: the crust, mantle, inner core, and outer core. The following defines each division. (Note: numbers representing the thickness and depth of these layers differ depending on the reference; thus, the numbers here should be taken as approximations):

Crust-The Earth’s crust is the outermost layer and is the most familiar, since people live on the outer skin of the crust. It is rigid, brittle, and thin compared to the mantle, inner core, and outer core. Because of its varying characteristics, this outer layer is divided into the continental and oceanic crusts.

Mantle-In general, the Earth’s mantle lies beneath the crust and above the outer core, averaging about 1,802 miles (2,900 kilometers) thick and repre· senting 68.3 percent of the Earth’s mass. A transition zone divides this layer into the upper and lower mantles.

Outer core-The liquid outer core is a layer between 1,793 and 3,762 miles (2,885 and 5,155 kilometers) deep in the Earth’s interior. It is thought to move by convection (the transfer of heat through the circulating motion of particles-in this case, the material that makes up the outer core), with the movement possibly contributing to the Earth’s magnetic field. The outer core represents about 29.3 percent of the Earth’s total mass.

Inner core-The inner core is thought to be roughly the size of the Earth’s Moon. It lies ata depth of 3,762 to 3,958 miles (5,150 to 6,370 kilometers) beneath the Earth’s surface and generates heat close to temperatures on the sun’s surface. It represents about 1.7 percent of the Earth’s mass and is thought to be composed of a solid iron-nickel alloy suspended within the molten outer core

Do geologists subdivide the Earth in any other way

Yes, geologists have another way of looking at the Earth’s interior layers. The following list refers to this view:

Lithosphere-The lithosphere (Ii/has is Greek for “stone”) averages about 50 miles (80 kilometers) thick and is composed of both the crust and part of the upper mantle. Overall, it is more rigid than deep, yet more molten mantle and cool enough to be tough and elastic. It is thinner under the oceans and in volcanically active continental regions, such as the Cascades in the western United States. The lithosphere is physically broken up into the brittle, moving plates containing the world’s continents and oceans. These lithospheric plates appear to “float” and move around on the more ductile asthenosphere. (For more on plate tectonics, see below).

Asthenosphere-A relatively narrow, moving zone in the upper mantle, the asthenosphere (asthenes is Greek for “weak”) is generally located between 45 to 155 miles (72 to 250 kilometers) beneath the Earth’s surface. It is composed of a hot, semi-solid material that is soft and flowing after being subject- ed to high temperatures and pressures; the material is thought to be chemically similar to the mantle. The asthenosphere boundary is closer to the sur~ face-within a few miles-under oceans and near mid-ocean ridges than it is beneath landmasses. The upper section of the asthenosphere is thought to be the area in which the lithospheric plates move, “carrying” the continental and oceanic plates across our planet. The existence of the asthenosphere was theorized as early as 1926, but it was not confirmed until scientists studied seismic waves from the Chilean earthquake of May 22, 1960.

What is the difference between compositional and mechanical layering of the Earth?

When scientists talk about the Earth’s crust (oceanic or continental), mantle, and cores, they are discussing layers with distinct chemical compositions; thus, it is referred to as compositional layering. The lithosphere and asthenosphere differ in terms of their mechanical properties (for example, the lithosphere moves as a rigid shell while the asthenosphere behaves like a thick, viscous fluid) rather than their composition, so this is why the term mechanical layering applies.

Who gave the first scientific explanation of the Earth’s interior?

Empedocles, a philosopher who lived during the 400s B.O:., was one of the first to formulate a scientific description of the Earth’s interior. He believed the inside of the Earth was composed of a hot liquid. In fact, Empedocles was close to the truth. Modern scientists realize that the Earth’s interior does not hold mythical beings but megatons of rock and molten matter