All about our Earth
Layers of the Earth
• Scientist think that as the Earth was
forming the denser materials, such as
iron and nickel, sank to the center due
gravity and the increase in temperature.
The less dense material moved toward
the surface and all the other material
settled between the surface and the
center.
• The layers of the
Earth are crust,
mantle, inner core and
outer core.
Crust
• There are two types of crust:
Continental (where we live) and
Oceanic (under the ocean).
• The crust is the least dense, thinnest
and coolest layer of rock.
• The boundary between the crust and
the next layer, the mantle, is called
the Moho.
Lithosphere
• The lithosphere layer includes
the crust and the upper
mantle. It is hard and rigid and
makes up the tectonic plates.
The tectonic plates float on the
mantle and constantly move.
Mantle
• The mantle is made of two parts the
asthenosphere and the mesosphere. The
thickest layer of about 67% of Earth’s mass.
It is made of molten rock with the temperature
between 870°C - 4400°C. The part of the
mantle closest to the core becomes hotter
causing a convection current throughout the
liquid. Convection current is when hot liquid
rises (less dense) and cool liquid sinks
(denser). This movement causes the plates
to move.
Core
The core is made of two parts – the Inner
Core and the Outer Core
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Outer Core
Less dense than inner core
Temperature 4400°C –
6100°C
Liquid
Made of both iron and
nickel
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Inner Core
More Dense
Temperature 7000°C –
8000°C
Solid
Mostly made of iron and little
nickel
•C – Crust
•L- Lithoshpere
•A – Asthenosphere
•M – Mesosphere
•O – Outer Core
•I – Inner Core
The Difference between the two
types of Crust
• There are two types of lithospheric crust –
oceanic and continental. Continental has
a average thickness of 30 km. Continental
crust is mostly made of granite. Oceanic
crust has a thickness of 5-8 km thick. The
composition of oceanic crust is basalt.
• The lithospheric crust are made up of
tectonic plates which float on the
asthenosphere layer of soft, hot rock. The
hot, soft rock rises, cools, and sinks, then
is heated and rises again. This is called
convection currents.
• There are two proposed motions that can
take place: slab pull and ridge push.
– Slab pull occurs where gravity pulls the edge
of cool dense place into the asthenosphere
because the plates are ridged; the entire plate
is pulled along. (Located at subduction zones)
– Ridge push occurs when material from the
mid-ocean ridge slides downhill from the
ridge. The material pushes the rest of the
plates. (Located where plates are separating)
Pangaea
• Pangaea (Pangaea) – In early geologic time a super continent
existed that incorporated almost all the Earth’s land masses.
• Pangaea covered almost 1/3 of Earth’s surfaces. Pangaea (all
lands) was surrounded by a global ocean called “panthalassa” (all
seas).
• Pangaea was fully assembled 270 million years ago and began to
break up 200 million years ago.
• The idea of Pangaea was proposed by Alfred Wegener in 1912 as
part of his continental drift theory.
Continental Plates
• Shortly after the earth was formed the crust broke up into huge thick
plates that drift on the mantle. The plates are made of rock and drift
all over the globe – they move both horizontally (sideways) and
vertically (up and down). Over long periods of time, the plates also
change in size as their margins are added to, crushed together or
pushed back into earth’s mantle.
• The Pacific Ring of Fire is mainly made up of the plate boundaries
that border the Pacific Ocean basin. The pacific ring of fire is a
region of high earthquake and volcanic activity that surrounds the
majority of the Pacific Ocean Basin.
Continental Drift
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Continental drift is the theory that the continents have moved. Alfred
Wegener was a German scientist that proposed the idea of continental drift.
Wegener based his theory on fossil evidence, climate change evidence and
geological evidence.
Fossils – Ancient reptile fossils of the mesosaursus were discovered
in South America and West Africa – but nowhere else in the world. This is
evidence that these two land masses were joined.
Climate – Greenland today lies near the arctic circle yet fossils of
tropical plants lie near its shores – evidence that Greenland was once
somewhere else.
Geology – the type of rock found in Brazil matched that of rock in
Western Africa. Limestone layers in the Appalachian mountains of North
America were exactly like the limestone in Scotland’s Highlands.
No one believed Wegener because he couldn’t find a way to make the
continents move. Plate tectonics is the theory that explains continental drift.
Convergent Boundaries
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A plate boundary is where two continental plates are next to each other. Like the
boundary between Georgia and South Carolina. What the plates do determines the
type of boundary that exists. There are three types of boundaries, convergent,
divergent and transformation.
When two plates move toward each other and collide – this is a convergent plate
boundary. What happens when two plates collide depends on the type of plates.
Oceanic & Continental Convergence
When continental and oceanic plates collide something called “subduction” occurs.
The oceanic plate sinks under the continental plate because the oceanic plate is
denser. The oceanic crust sinks back into Earth’s mantle where it melts because of
the intense heat & friction. This collision causes cracks in plates. The magma rises
up the cracks creating volcanoes. The subduction also causes deep ocean trenches.
Continental & Continental Convergence
When two continental plates collide one plate goes slightly under the other but
subduction does not occur because the density of the plates is almost the same. The
pressing together of two plates pushes both plates up and the crust folds. Fold
Mountains are formed at these boundaries.
Oceanic & Oceanic Convergence
Deforming the Earth’s Crust
• Plate interactions cause Faults
• Faults are fractures, or breaks, in earth’s
lithosphere, along which blocks of rock
move past each other.
• Reverse Faults – Along a reverse fault the
block of rock above the fault plane moves
up relative to the other block. This occurs
at convergent boundaries.
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Divergent Boundaries
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New crust is created as two or more plates pull apart – this is called a
divergent boundary. A divergent boundary is considered constructive
because new crust is made.
Divergent boundaries are located at the boundary of oceanic plates or at the
boundary of continental plates. The mid-ocean ridge in the ocean is an
example of a divergent boundary. At the mid-ocean ridge the plates move
away from each other and the magma comes up from the mantle where it is
cooled by the ocean water and creates new crust.
In Africa there is a divergent boundary where two continental plates pull
away from each creating the Great Rift Valley.
Normal Faults – Along a normal fault the block of rock above the fault
planes slides down relative to the other block. Earth quakes along normal
faults are common near divergent boundaries.
• Sea Floor Spreading - When the sea floor was mapped in the 1950’s
scientists found that the ocean floor wasn’t smooth but instead had a
mid-ocean ridge – which are large mountains rising from the ocean
floor. These mid-ocean ridges were created by sea floor spreading.
• As the tectonic plates that make up the ocean floor move away from
each other hot magma from the Earth’s mantle bubble up. The
magma is cooled by sea water. The new rock forms a new part of
the Earth’s crust. Over time new oceanic crust pushes older crust
farther away.
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Age of the Sea Floor- The age of the continental crust is about
4.6 billion years old – whereas the age of the sea floor is much
younger. The sea floor is constantly being renewed and destroyed.
The newest ocean floor is being created all the time. The oldest sea
floor is about 160 million years old. Ocean trenches are long narrow
depressions in the sea floor along convergent plate boundaries. At
this place on the plate (the denser plate) moves under another plate
where it melts and is destroyed.
Transform Boundaries
• A transform plate boundary is one where two plates slide laterally
past each other. However, movement is not smooth because of
friction between the rocks of the two plates. Therefore, sometimes
two plates would get stuck and lock together. But since the
convection currents of the underlying magma are still dragging the
plates, much tension and pressure is built up at the transform
boundary. When there is enough built up pressure, rocks in the
plates break and are jerked apart – resulting in an earth quake.
• A transform boundary creates a strike-slip fault – along a strike slip
fault the rock moves sideways on either side of the fault plane.
These types of faults occur at transformation boundaries.
Types of Mountains
Volcanoes
Earthquakes
Minerals are all around us.
• Minerals have four characteristics
o Formed in nature
o They are solids
o Have a definite chemical makeup.
Minerals are always made up of the same materials in the
same proportions.
o Have a crystal structure.
crystal are solid with the atoms arranged in an orderly,
repeating, three-dimensional pattern.
Crystal structures can determine a mineral's properties,
and not all minerals have the same crystal structure.
 Scientists classify minerals into groups based on their
chemical makeup.
oSilicates and Non-silicate (most common)
making up 90 percent of the rocks in Earth's
crust.
They contain oxygen and silicon bonded together.
Common silicates are quartz, feldspar, and mica.
oCarbonates (second most common)
They oxygen and carbon bonded together.
 A common carbonate is calcite.
oOxides are important minerals.
Metals are refined from oxides for human use.
They contain a metallic element bonded to
oxygen.
 A common oxide is hematite, a source of iron.
A mineral is identified by its properties
•A mineral's appearance helps identify it.
Color - they can be almost any color,
but most have a limited color range.
Because different minerals can be the
same color, this is not the best method
to identify them.
•Streak - the color of the powder left
behind when a mineral is scraped
across a surface. Streak is a better
• Luster - way in which light reflects
from a mineral's surface.
o Two major types of luster:
Metallic and Nonmetallic.
o The luster can dull if exposed to
the atmosphere or to water, but if
the mineral is broken to reveal a
fresh surface, the characteristic
luster can be seen.
The way a mineral breaks helps identify it.
oCleavage - tendency of a mineral to break
along flat surfaces.
the bonds of atoms in the crystal structure are
weaker in one or more directions. These are
the directions in which the mineral tends to
break.
oFracture - tendency of a mineral to break
into irregular pieces.
the bonds that join the atoms are fairly equal
in strength in all directions. The mineral
breaks into different shapes, not along flat
surfaces.
Density and Hardness help identify Minerals.
• Density - the amount of mass per unit volume.
o Density can be very helpful in identifying minerals, including
some that look alike.
o Example, gold and pyrite, as gold is much more dense than
pyrite.
• Hardness - a mineral's resistance to being scratched.
o It is determined by its crystal structure and the strength of its
bonds.
Harder minerals have stronger bonds.
o The Mohs scale is often used to describe a mineral's
hardness.
Talc is the softest and diamond is the hardest.
Minerals higher on the scale can scratch minerals lower
on the scale.
 Some minerals have special properties.
o Carbonates react with acid and form bubbles
of carbon dioxide.
o Fluorite and other minerals fluoresce, or glow
when exposed to ultraviolet light.
o Magnetite and other magnetic minerals
attract a loosely held magnet.
o Some minerals are radioactive.
Mohs Hardness Scale
Hardness Mineral
1
Talc
2
Gypsum
3
4
Calcite
Fluorite
5
Apatite
Associations and Uses
Talcum Powder
Plaster of Paris, Formed when
seaweed evaporates
Limestone, Found in most shells
Prevents Tooth Decay
6
7
Hungry! You must have a big
“appetite”
Orthoclase Is a Feldspar
Quartz
Watches and Computer Chips
8
9
10
Topaz
Corundum
Diamond
November Birthstone
Sapphire and Ruby
A cutting Tool
Hardness of Some Items
2.5
2.5-3
3
4-4.5
4-5
5.5
6-7
6.5
7+
Fingernail
Gold, Silver
Copper Penny
Platinum
Iron
Knife Blade
Glass
Iron Pyrite
Hardened Steel File
2.3 Minerals are valuable resources.
 Minerals have many uses in industry and the
arts.
oHematite and chromites are minerals from
which people obtain metals. Quartz, another
mineral, is used to make glass and silicon
computer chips.
oMica and talc are minerals used in paints.
Certain minerals known as gemstones are
used to make jewelry. Amethyst, diamond,
and emerald are examples of gemstones.
Metals such as silver and gold are also used
in jewelry making and other decorative arts.
 Minerals form in many ways.
oAs water evaporates, elements from substances
dissolved in water can join to form mineral
crystals.
oAs hot water cools, minerals dissolved in the
water separate from the water and become solid
again.
oAs molten rock cools, atoms join together to form
different minerals.
oHeat and pressure within Earth cause new
minerals to form as bonds between atoms break
and join again in new ways.
oA few minerals are produced by living things. For
example, some ocean animals produce
carbonate minerals to form shells.
 Minerals must be removed from the ground, or
mined, before they can be used to make
products. Mining occurs close to Earth's
surface, as well as deep underground. Miners
recover ores, which are rocks that contain
enough of a valuable mineral to be mined for a
profit.
oSurface mining recovers minerals at or near
Earth's surface. Examples of surface mines
are strip mines and open-pit mines.
oDeep mining recovers minerals far below
Earth's surface. Deep mine tunnels can be
horizontal or vertical, depending on where the
ore is located.