Download The Mantle

Layers of the Earth
Volcano World
http://volcano.oregonstate.edu/earths-layers-lesson-1
The Four Layers
The Earth is composed of four different layers. Many geologists believe that as the Earth cooled the heavier,
denser materials sank to the center and the lighter materials rose to the top. Because of this, the crust is made of
the lightest materials (rock- basalts and granites) and the core consists of heavy metals (nickel and iron).
The crust is the layer that you live on, and it is the most widely studied and understood. The mantle is much
hotter and has the ability to flow. The Outer and Inner Cores are hotter still with pressures so great that you
would be squeezed into a ball smaller than a marble if you were able to go to the center of the Earth!!!!!!
The Crust
The Earth's Crust is like the skin of an
apple. It is very thin in comparison to the
other three layers. The crust is only about
3-5 miles (8 kilometers) thick under the
oceans(oceanic crust) and about 25 miles
(32 kilometers) thick under the
continents (continental crust). The
temperatures of the crust vary from air
temperature on top to about 1600 degrees
Fahrenheit (870 degrees Celcius) in the
deepest parts of the crust. You can bake a
loaf of bread in your oven at 350 degrees
Fahrenheit , at 1600 degrees F. rocks
begin to melt.
The crust of the Earth is broken into many pieces called plates. The plates "float" on the soft, plastic mantle
which is located below the crust. These plates usually move along smoothly but sometimes they stick and build
up pressure. The pressure builds and the rock bends until it snaps. When this occurs an Earthquake is the result!
Notice how thin the crust of the Earth is in comparison to the other layers. The seven continents and ocean
plates basically float across the mantle which is composed of much hotter and denser material.
The crust is composed of two basic rock types granite and basalt. The continental crust is composed mostly of
granite. The oceanic crust consists of a volcanic lava rock called basalt.
Basaltic rocks of the ocean plates are much denser and heavier than the granitic rock of the continental plates.
Because of this the continents ride on the denser oceanic plates. The crust and the upper layer of the mantle
together make up a zone of rigid, brittle rock called the Lithosphere. The layer below the rigid lithosphere is a
zone of asphalt-like consistancy called the Asthenosphere. The asthenosphere is the part of the mantle that flows
and moves the plates of the Earth.
The Mantle
The mantle is the layer located directly under the sima. It is the largest layer of the Earth, 1800 miles thick. The
mantle is composed of very hot, dense rock. This layer of rock even flows like asphalt under a heavy weight.
This flow is due to great temperature differences from the bottom to the top of the mantle. The movement of the
mantle is the reason that the plates of the Earth move! The temperature of the mantle varies from 1600 degrees
Fahrenheit at the top to about 4000 degrees Fahrenheit near the bottom!
The mantle is made of much denser, thicker material, because of this the plates "float" on it like oil floats on
water.
Many geologists believe that the mantle "flows" because of convection currents. Convection currents are
caused by the very hot material at the deepest part of the mantle rising, then cooling, sinking again and then
heating, rising and repeating the cycle over and over. The next time you heat anything like soup or pudding in a
pan you can watch the convection currents move in the liquid. When the convection currents flow in the mantle
they also move the crust. The crust gets a free ride with these currents. A conveyor belt in a factory moves
boxes like the convection currents in the mantle moves the plates of the Earth.
Outer Core
The core of the Earth is like a ball of very hot metals. (4000 degrees F. to 9000 degrees F.) The outer core is so
hot that the metals in it are all in the liquid state. The outer core is located about 1800 milesbeneath the crust
and is about 1400 miles thick. The outer core is composed of the melted metals nickel and iron.
Inner Core
The inner core of the Earth has temperatures and pressures so great that the metals are squeezed together and
are not able to move about like a liquid, but are forced to vibrate in place as a solid. The inner core begins about
4000 miles beneath the crust and is about 800 miles thick. The temperatures may reach 9000 dgrees F. and the
pressures are 45,000,000 pounds per square inch. This is 3,000,000 times the air pressure on you at sea level!!!
Layers Of The Earth: What Lies Beneath Earth's Crust
http://www.forbes.com/sites/trevornace/2016/01/16/layers-of-the-earth-lies-beneath-earths-crust/#67ca57358e6d
Trevor Nace ,
The layers of Earth provide geologists and geophysicists
clues to how Earth formed, the layers that make up other
planetary bodies, the source of Earth's resources, and
much more. Modern advances have allowed scientists to
study what lies beneath our feet in more detail than ever
before and yet there still remains significant gaps in our
understanding.
I hope this guide will walk you through the layers of the
Earth, provide a general sense of our understanding and
our current gaps. Keep in mind that this is an area of
ongoing research and is likely to become more refined in
the coming years and decades.
The Layers Of Earth
The Earth has layers not unlike an onion and can be dissected to understand the physical and chemical
properties of each layer and its influence on the rest of the Earth. Generally speaking, Earth has 4 layers: the
outer crust that we live on, the plastic-like mantle, the liquid outer core, and the solid inner core.
When differentiating the layers, geologists lump subdivisions into two categories, either rheologically or
chemically. Rheological differentiation speaks to the liquid state of rocks under tremendous pressure and
temperature. For instance, rock will respond very differently to strain under normal atmospheric temperatures
and pressures as compared to fewer than thousands of kilometers of rock. If we subdivide the Earth based on
rheology, we see the lithosphere, asthenosphere, mesosphere, outer core, and inner core. However, if we
differentiate the layers based on chemical variations, we lump the layers into crust, mantle, outer core, and inner
core.
To understand the difference in various portions of the mantle or outer versus inner core you must understand
phase diagrams, which I will speak on below.
Earth's Crust
The crust is what you and I live on and is by far the thinnest of the layers of earth. The thickness varies
depending on where you are on earth, with oceanic crust being 5-10 km and continental mountain ranges being
up to 30-45 km thick. Thin oceanic crust is denser than the thicker continental crust and therefore 'floats' lower
in the mantle as compared to continental crust. You will find some of the thinnest oceanic crust along mid ocean
ridges where new crust is actively being formed. In comparison, when two continents collide as in the case of
the India Plate and Eurasia Plate, you get some of the thickest sections of crust as it is crumpled together.
The temperatures within Earth's crust will vary from air temperatures at the surface to approximately 870
degrees Celsius in deeper sections. At this temperature, you begin to melt rock and form the below-lying
mantle. Geologists subdivide Earth's crust into different plates that move about in relation to one another. Given
that Earth's surface is mostly constant in area, you cannot make crust without destroying a comparable amount
of crust. With convection of the underlying mantle, we see insertion of mantle magma along mid ocean ridges,
constantly forming new oceanic crust. However, to make room for this, oceanic crust must subduct (sink below)
continental crust. Geologists have studied extensively the history of this plate movement, but we are sorely
lacking in determining why and how these plates move the way they do.
Earth's crust "floats" on top of the soft plastic-like
mantle below. In some instances mantle clearly
drives changes in the crust, as in the Hawaiian
Islands. However, there is ongoing debate whether
oceanic crust subduction and mid ocean ridge
spreading is driven by a push or pull mechanism.
In very broad terms, oceanic crust is made up of
basalt and continental crust is made up of rocks
similar to granite. Below the crust is a solid
relatively cooler portion of the upper mantle that is
combined with the crust to make the
lithosphere layer. The lithosphere is physically
distinct from the below-lying layers due to its cool
temperatures and typically extends 70-100 km in depth.
Below the lithosphere is the asthenosphere layer, a much hotter and malleable portion of the upper mantle. The
asthenosphere begins at the bottom of the lithosphere and extends approximately 700 km into the Earth. The
asthenosphere acts as the lubricating layer below the lithosphere that allows the lithosphere to move over the
Earth's surface.
Earth's Mantle
The mantle is the layer of the earth that lies below the crust and is by far the largest layer making up 84% of
Earth's volume. The mantle starts at the Mohorovicic Discontinuity, also known as the Moho. The Moho is
defined as the density contrast from less dense crust to denser mantle and where seismic wave velocities
increase. The mantle acts similar to plastic and at very high temperatures and pressures the rock is deformable
at geologic timescales. This deformation causes a convection like process in the mantle where you have larigescale upwelling and downwelling zones.
The mantle extends down to 2,890 km into the Earth's surface Temperatures that range from 500 to 900 degrees
Celsius in the upper portion to over 4,000 degrees Celsius near the core boundary. Earth's mantle is believed to
be composed of bulk mineralogy similar to peridotite. Gem quality peridotite is called peridot, so next time
you're in a jewelry shop take a look at the peridot and you'll be looking at something similar to 84% of Earth!
The video above provides a glimpse into the global circulation of mantle magma around the Earth. Of course,
this is greatly simplified but provides a schematic of the process creating mid ocean ridges, volcanoes, and
mountains.
Earth's Outer Core
The outer core is the liquid largely iron layer of the earth that lies below the mantle. Geologists have confirmed
that the outer core is liquid due to seismic surveys of Earth's interior. The outer core is 2,300 km thick and goes
down to approximately 3,400 km into the earth. No one has ever seen the outer core but based on a number of
indicators, geologists believe the outer core is 80% iron, some nickel and a number of different lighter elements.
When Earth was just beginning to cool billions of years ago, heavier elements sunk down into the center of the
Earth, while less dense elements rose to the surface. Therefore, we see a general increase in density, as you get
closer to the center of the Earth.
The outer core is hot enough to be melted but not under quite enough pressure to make the iron solid again, as
seen in the inner core. The temperature of the outer core ranges from about 4,030 to 5,730 degrees Celsius.
Amazingly, the outer core is fluid enough and low enough in viscosity that it may spins faster than the entire
Earth. This differential velocity of spinning, along with convection and turbulent flow of the iron outer core,
creates Earth's magnetic field.
A schematic of Earth's magnetic field (Credit: NASA)
Earth's Inner Core
The inner core is the centermost layer of Earth and is in many ways similar to the outer core. It is also primarily
iron and nickel and has a radius of about 1,220 km. The differentiation between the outer core and inner core is
density driven. The pressures become high enough that despite very high temperatures, the inner core is solid. It
is also enriched in unusual heavy elements including gold, silver, platinum, palladium, and tungsten.
Temperatures reach up to 5,400 degrees Celsius and pressures up to 360 gigapascal. The inner core is about
70% of the Moon's radius and is approximately the same temperature as the surface of the Sun!