THE EARTH’S LAYERS
Continued
TO REVIEW!!
• The crust is less than 1% of Earth by mass.
• The mantle (inner and outer) represents about 68% of Earth by mass.
• The core (inner and outer) represents about 31% of Earth by mass.
• The mantle has two layers: a solid-ish layer and a more molten, liquid-ish
layer.
• The core has two layers: the outer core is liquid. The inner core is solid. Both
sections of core are comprised of iron and nickel.
• The inner core is the densest layer of earth.
MORE ON THE CORE
• The density of Earth’s surface layers is much less than the overall density of the
planet.
• Calculations indicate that the core is about 85% iron metal with nickel metal making
up much of the remaining 15%.
• If Earth’s core were not metal, the planet would not have a magnetic field. Metals
such as iron and nickel are magnetic, but rock, which makes up the mantle and
crust, is not.
• Metallic meteorites are thought to be representative of the core. The 85-15% ratio of
nickel and iron is seen mirrored in meteorite fragments.
• Scientists know that the outer core is liquid and the inner core is solid because of Swaves and P-waves. Also because of Convection currents.
• (the heat that keeps the outer core from solidifying is produced by the breakdown
of radioactive elements in the inner core.)
MORE ON THE MANTLE:
CONVECTION AND CONDUCTION
• Heat flows in two different ways within the earth: Convection and
Conduction.
• Conduction: Heat is transferred through rapid collisions of atoms, which can only
happen if the material is solid. Heat flows from warmer to cooler places until all
are the same temperature. The mantle is hot mostly because of heat conducted
from the core. (Think of Heat/Electricity conductors)
• Convection: If a material is able to move, even if it moves very slowly,
convection currents can form.
• Convection in the mantle is the same as convection in a pot of water on a
stove: the currents start forming near the core where the material heats up.
As the core heats the bottom layer of mantle material, particles move more
rapidly, decreasing its density and causing it to rise. The rising material begins
the convection current.
MORE ABOUT THE CRUST: DID YOU
KNOW THE CRUST HAS LAYERS?
• There is the lithosphere, asthenosphere, and mesosphere
• Lithosphere: composed of both crust and a portion of the upper mantle that
behaves more brittle/rigid/solid.
• Asthenosphere: composed partially of molten upper mantle material that
can “flow” and is kinda liquid
• Mesosphere: composed of mantle under both the Lithosphere and
Asthenosphere, but above the outer core.
• (Think of it this way: Least deep, Average depth, then Mostly deep.)
• The Difference between mesosphere and asthenosphere is likely due to
density and rigidity differences and other physical properties, not really due
to any difference in chemical composition.
THE CRUST IS WEIRDER AND MORE
COMPLICATED THAN WE THOUGHT
• If you think about it, this makes sense: the crust is thinner at, say, a desert
landscape than at Mt. Everest.
• Also, though, the crust is thinner by the ocean. Thus the crust can be divided
into two very different types: each with their own distinctive properties,
chemical and physical.
• Oceanic Crust and Continental Crust.
Crust
Thickness
Density
Composition Rock Types
Oceanic
5-12 km (3-8
mi)
3.0 g/cm3
Mafic
Basalt and
gabbro
Continental
Avg. 35 km
(22 mi)
2.7 g/cm3
Felsic
All Types
OCEANIC AND CONTINENTAL
CRUST
• Oceanic crust: composed of mafic magma that erupts on the seafloor to create basalt
lava, which flows or cools deeper down to create the intrusive igneous rock gabbro.
• All of these are different kinds of rocks, with different physical and chemical properties, and
different densities. The gabbro is considered deformed because it is created because of
intense faulting at the eruption site of a volcano, be it under the crust or above it.
• Sediments, primarily muds and the shells of tiny sea creatures, coat the seafloor.
Sediment is the thickest near the shore where it comes off the continents in rivers and on
wind currents.
• Continental crust: composed of many different types of igneous, metamorphic, and
sedimentary rocks.
• The average composition is granite, which is much less dense than the mafic rocks of the
oceanic crust.
• Because granite is thick and has relatively low density, continental crust will rise higher on the
mantle than oceanic crust, which sinks into the mantle. It forms basins which, when filled with
water, form the planet’s oceans.
SO…LITHOSPHERE
• When we think of the crust, we basically think of the Lithosphere. And, if you
think about it, it makes a lot more sense that the Atmosphere is included as a
layer of the earth.
• Atmosphere, Lithosphere, Asthenosphere, Mesosphere, core. 
• The Lithosphere is the outermost, mechanical layer of the earth, which
behaves as a brittle, rigid solid. It’s about 100 km. thick.
• The definition of lithosphere is based on how the earth materials behave,
which is why it includes the part of the mantle, which is brittle. Since it is rigid
and brittle and the inner layers of the earth are not, stress actions cause the
lithosphere to crack and break.
• Otherwise known as an earthquake.