Earth Science Notes: Earth’s Layers
Standards:
7.1 Analyze the characteristics of Earth’s layers and the location of the major plates.
CFU’s:
7.4 Recognize that Earth’s layers have different thickness, states of matter, densities and chemical makeup.
Key Learning (SPI’s):
24: Differentiate among the characteristics of Earth’s three layers.
25: Recognize that lithospheric plates on the scale of continents and oceans continually move at rates of
centimeters per year.
Prior Knowledge:
Students must have an understanding of the value of a centimeter.
Students must understand the basic difference between a solid and liquid.
Students must have a basic understanding of density and pressure.
Scaffolding:
1.) After Earth first formed in a molten state, the surface cooled into solid rock.
2.) The solid Earth’s three layers consist of the outer crust; a hot mantle with convection movement of material;
and a dense, metallic core.
3.) The entire outer layer of Earth, including the continents and ocean floor, consists of separate plates that rest
on a dense, hot, somewhat melted mantle layer.
Misconceptions:
Students may assume that the crust, mantle, core sequence is the same as the lithosphere, asthenosphere,
mesosphere sequence, but in fact they are different. The former is defined by the chemical properties and
composition and the latter is defined by physical properties such as fluid or rigid due to heat and pressure. As
well, the crust, etc. are considered compositional layers of the earth, while lithosphere, etc. are considered
structural layers of the earth. It may be necessary to go over the terms compositional and structural.
Students may think that the theory of plate tectonics has been around for a long time, when in fact, it has only
been accepted within the last fifty years or so. Scientists have not fully identified the mechanisms behind plate
movement, but plate tectonics is the best, current explanation we have.
Students may think that the plate boundaries follow continent boundaries but this is not true, of the six major
plates, they all consist of some portion of a continent along with oceanic crust.
Vocabulary:
crust: the thin and solid outermost layer of Earth; it is located above the mantle.
mantle: the layer of rock between Earth’s crust and core.
inner core: the solid, dense center of our planet that extends from the bottom of the outer core to the center.
outer core: the liquid layer of Earth’s core that lies beneath the mantle and surrounds the inner core.
lithosphere: the outermost, rigid layer of Earth.
asthenosphere: the layer of the mantle on which pieces of the lithosphere move.
mesosphere: located beneath the asthenosphere it is the strong lower part of the mantle.
tectonic plates: a block of lithosphere that consists of the crust and the rigid, outermost part of the mantle.
Notes:
Scaffolding #1: After Earth first formed in a molten state, the surface cooled into solid rock.
What is the difference between a solid and liquid?
Phase
Shape
Volume
Heat Energy (HE) Intermolecular Forces (IF)
definite
definite
least
strongest
Solid
indefinite
definite
> solid/ <gas
< solid/ > gas (able to flow)
Liquid
indefinite
indefinite
most
weakest
Gas
Heat Energy/ Intermolecular Forces relationship: as HE increases, IF decreases and vice versa.
Example: Water (H2O)
solid- ice, < 32 degrees, maintains its shape and cannot be compressed.
liquid- water, 32 degrees to 212 degrees, takes the shape of its container and cannot be compressed.
gas- water vapor (steam) > 212 degrees, takes the shape of its container, can escape its container and can be
compressed.
Scaffolding #2: The solid Earth’s three layers consist of the outer crust; a hot mantle with convection
movement of material; and a dense, metallic core.
Compositional layers of Earth are defined by their composition. (chemical makeup, chemical properties)
Structural layers of Earth are defined by their properties, rigid and fluid respectively. (physical properties)
Compositional Layers: Defined by their composition (chemical properties)
Crust: The outermost layer of our Earth.
Thickness: 10 km (under oceans) to 70 km (under continents); 1% of Earth’s mass
Composition: alumino silicates (aluminum, silicon and oxygen)
Properties: rigid and brittle, consists of continental (granite) and oceanic (basalt) portions
Mantle: The layer of rock between Earth’s crust and the core.
Thickness: 2,900 km; 66% of Earth’s mass
Composition: ferromagnesium silicates (iron, magnesium, silicon and oxygen)
Properties: upper mantle is rigid, lower mantle is fluid. This is where most of the internal heat of Earth is
located. Large convective cells in the mantle circulate heat and may drive plate tectonic processes.
Outer Core: The liquid layer of Earth’s core that lies beneath the mantle and surrounds the inner core.
Thickness: 2,300 km; 33% of Earth’s mass (together with the inner core)
Composition: nickel-iron alloy (metal mixture)
Properties: liquid, Earth’s magnetic field is believed to be controlled by the liquid outer core (nickel and iron
are ferromagnetic).
Inner Core: The solid, dense center of our planet that extends from the bottom of the outer core to the center.
Thickness: 1,200 km radius
Composition: iron
Properties: dense, solid
Structural Layers: Defined by their physical properties
Lithosphere: The outermost, rigid region of Earth.
Depth: approximately 50 miles/100 km
Correlating Earth Layers: crust and solid portion of upper mantle
Properties: rigid, brittle, broken into plates that slowly move independently of one another. The interaction of
these plates can cause earthquakes and volcanoes along with shaping mountain ranges, ocean ridges and ocean
trenches. The lithosphere essentially floats on top of the asthenosphere.
Asthenosphere: The region of the mantle on which pieces of the lithosphere move.
Depth: 100 – 500 km
Correlating Earth Layers: the fluid region of the mantle
Properties: fluid, exists at a higher temperature and pressure than the lithosphere so it is capable of flowing.
This property of the asthenosphere is why the plates in the lithosphere move.
Mesosphere: Located beneath the asthenosphere, it is the strong lower region of the mantle.
Depth: 2,500 km
Correlating Earth Layers: lower portion of mantle
Properties: fluid
crust
lithosphere (crust and upper mantle, thus rigid and brittle)
mantle
asthenosphere (middle, fluid portion of mantle)
mesosphere (strong lower part of the mantle)
outer core
inner core
How do we know so much about the interior of the earth when we have never been there? The answer lies
within earthquakes. When an earthquake happens, it sends out seismic waves (sound waves essentially) that
travel through the earth. These seismic waves travel at different speeds through different substances depending
on the density and composition of the substance. We use seismographs to measure the speed of these waves as
they travel through the earth and it helps us to create a map of our interior.
Scaffolding #3: The entire outer layer of Earth, including the continents and ocean floor, consists of
separate plates that rest on a dense, hot, somewhat melted mantle layer.
Because the lithosphere is rigid and brittle, it can break. It currently exists in sixteen different pieces that we call
tectonic plates. These large chunks of the crust “float” on the asthenosphere (fluid portion of mantle)
underneath and so they move independently of one another. This movement is very slow, at the rate of 1-20
cm/year, but over thousands of years it adds up.