EARTH CRUST LAYERS AND THEIR COMPOSITION

There is more to the Earth than what we can see on the surface. In fact, if you were able to hold the Earth in your hand and slice it in half, you’d see that it has multiple layers. But of course, the interior of our world continues to hold some mysteries for us.

However, advances in seismology have allowed us to learn a great deal about the Earth and the many layers that make it up. Each layer has its own properties, make-up, and characteristics that affects many of the key processes of our planet. They are, in order from the exterior to the interior – the crust, the mantle, the outer core, and the inner core.

The Earth can be divided into one of two ways – mechanically or chemically. Mechanically – or rheologically, meaning the study of liquid states – it can be divided into lithosphere, asthenosphere, mesospheric mantle, outer core, and the inner core. But chemically, which is the more popular of the two, into the crust, upper mantle, lower mantle, outer core, and inner core.

History of Study:

Since ancient times, human beings have sought to understand the formation and composition of the Earth.The earliest known cases were unscientific in nature – taking the form of creation myths or religious fables involving the gods. However, between classical antiquity and the medieval period, several theories emerged about the origin of the Earth, its true shape, and its place in the cosmos.

Most of these tended towards the “Flat-Earth” view of our planet’s physical form. This was the view in the Mesopotamian culture, where the world was portrayed as a flat disk afloat in an ocean. To the Mayans, the world was flat, and at it corners, four jaguars (known as bacabs) held up the sky. The ancient Persians speculated that the Earth was a seven-layered ziggurat (or cosmic mountain), while the Chinese viewed it as a four-side cube.

By the 6th century BCE, Greek philosophers began to speculate that the Earth was in fact round, and by the 3rd century BCE, the idea of a spherical Earth began to become articulated as a scientific matter

However, it was not until the 16th and 17th centuries that a scientific understanding of planet Earth and its structure truly began to advance. In 1692, Edmond Halley (discoverer of Halley’s Comet) proposed what is now known as the “Hollow-Earth” theory.

Halley’s construct was a method of accounting for the values of the relative density of Earth and the Moon that had been given by Sir Isaac Newton, in his Philosophiæ Naturalis Principia Mathematica (1687) – which were later shown to be inaccurate.

The layering of Earth has been inferred indirectly using the time of travel of refracted and reflected seismic waves created by earthquakes. The core does not allow shear waves to pass through it, while the speed of travel (seismic velocity) is different in other layers. The changes in seismic velocity between different layers causes refraction owing to Snell’s law, like light bending as it passes through a prism. Likewise, reflections are caused by a large increase in seismic velocity and are similar to light reflecting from a mirror.

CRUST

The crust is the first layer of the earth. It is split up into two parts the continental crust, and the oceanic crust. The oceanic crust takes up 71% of the earths crust, and the other 29% of the crust is continental. The continental is made up of igneous rocks, and the oceanic crust is made up of sedimentary and basalt rocks.

Earth's crust is made up of several elements: oxygen, 47 percent; silicon, 27 percent; aluminum, 8 percent; iron, 5 percent; calcium, 4 percent; magnesium, potassium and sodium, 2 percent

The continental crust is older than the oceanic crust, some of the rocks are 3.9 billion years old. The density average of the oceanic crust is 3g/cm. The average density of the continental earth is 2.7g/cm. The temperature of the crust is around 200-400 degrees celsius. The crust is about 60 km thick under a continent and 5 km thick under the ocean. The crust is constantly moving  they move at about the same rate as fingernails grow. The crust is the layer where tectonic plates can be found.

MANTLE

The mantle is the second layer of the earth. It is split up into two different parts, the lithosphere (which is the top part) and the asthenosphere (which is the bottom part). 

The lithosphere is a dense rock made out of iron and nickel, the asthenosphere is a plastic like fluid. The temperature of the lithosphere is around 300 to 500 degrees celsius, and the asthenosphere is around 4500 degrees celsius. 

The mantle has the biggest volume of all the layers, the volume of it is 84% of the earth. It is 1,800 miles deep or 2,900 kilometers deep. In the mantle are convection currents which make the mantle move. The lower mantle heats up and rises and cools down then gets pushed down because it is heavier. The mantle grows a meter a year.

a)LITHOSPHERE

The lithosphere is the top layer of the mantle. The lithosphere includes having the crust in it. It is a cooler layer because it is farther from the inner core. The lithosphere is a dense rock made out of iron and nickel. 

The temperature of the lithosphere is 300-500 degrees celsius. Inside the lithosphere and asthenosphere are currents, called convection currents. They make the lithosphere and asthenosphere turn round and round. So because the lithosphere is denser it is being forced down closer to the core and then heats up then forces its way back up to the top because it is less dense.

b)ASTHENOSPHERE

The asthenosphere is the bottom layer of the mantle. It is a plastic like liquid made up of iron and nickel. The temperature of the asthenospere is 4500 degrees celsius. It is hotter than the lithosphere because it is closer to the inner core. 

Inside the asthenosphere and lithosphere are currents, they are called convection currents. So because the asthenosphere is less dense or lighter than the lithosphere is forces its way up to the top and foces the lithosphere down. It then cools down then gets forced back down by a hotter substance

c)CONVENCTION CURRENTS

Convection Currents happen in the Mantle. They go through bot the lithosphere and the asthenosphere. They make them move round and round. Since the asthenosphere is hotter, that makes it lighter or less dense, so it forces its way to the top. 

Meanwhile it is forcing the lithosphere to go down and take it's place, So the asthenosphere that moved up and cooled down, and the lithosphere that got forced down is heating up and then when it gets hot ebough it will force its way to the top and the whole cycle will start again. But these convection currents effect the earth and the tectonic plates. 

Because when the plates, say...... overlap one gets pushed under the other, and it would get pushed don to the convection currents, and because it is a dense material it would be forced down and it would melt and make a new crust. In the photo below that diagram would acctually be going on inside of the earth at this very moment!

OUTER CORE

The outer core is a liquid made up of iron and nickel. The temperature of the outer core is around 4400 degrees celsius. 

The depth of the outer core is 2, 890. This is one of the three layers that is putting pressure on the inner core. It is the second hottest layer, because it is the layer above the inner core, and it is the second farthest from the surface of the earth. Also it is said that the core is rotating faster than the rest of the earth but...... slower than previously believed! the outer core was discovered in 1936 by seismologist, Inge Lehmann.

INNER CORE

The Inner crust is the second thinnest layer. The inner core is hotter than the surface of the sun. The inner core is made out of iron and nickel. 

It is 5159 to 6378 km thick. The inner core is extremely hot and is the last layer. The inner core is 5505 degrees celsius. It is a solid because of all the pressure from the other layers putting there weight onto this layer. The inner core grows. The core was discovered in 1971..