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SOIL FORMATION
Weathering and Erosion

Two key processes to breaking down rock
 THEY
ARE NOT THE SAME THING
is the rock itself breaking down and
always happens first
 There
are 2 varieties of weathering: physical and chemical
 This is affected by temperature and chemicals
 Water is the most common chemical that weathers rocks
is the removal and transport of the rock
 This
is where the rock travels as either smaller rocks or
sediment
Soil Layers

Soil is composed of 4
layers typically:
O
horizon
 Top
A
layer of organic matter
horizon
 Weathered
rock mixed with
rich organic material
B
horizon
 Enriched
by deposited
minerals
C
horizon
 Little/no
organic matter
PLATE TECTONICS
Continental Drift


If you look at a map,
you can see that some
shapes look like they
could fit together like a
puzzle.
German meteorologist
Alfred Wegener thought
that the fit of the
continents wasn’t just a
coincidence.
Pangaea


Wegener suggested that all the continents were
joined together at some time in the past.
In 1912, he proposed the hypothesis of continental
drift.
 According to this hypothesis, continents have moved
slowly to their current locations.
 He suggested that all continents once were
connected as one large landmass that broke apart
about 200 million years ago.
 Pangaea
Pangaea
A controversial idea

Wegener’s idea about continental drift were
controversial.
 It wasn’t until long after Wegener’s death in 1930
that his basic hypothesis was accepted.
 He was unable to explain exactly how the
continents drifted apart.
Fossil Clues

Besides the puzzle like fit, fossils provided support
for continental drift.
 Fossils of the reptile Mesosaurus have been found in
South America and Africa.
 This swimming reptile lived in freshwater and on
land
 How could fossils be found on land separated
by huge amounts of SALT water?
 Wegener hypothesized that this reptile lived
on both continents when they were joined.
Rock Clues

If the continents were connected at one time, then
rocks that make up the continents should be the
same in locations where they were joined.
 Similar
 Parts
rock structures are found on different continents.
of the Appalachian Mtns are similar to those found in
Greenland and Western Europe.
 Rock structures found from eastern South America and
western Africa are similar
How could continents drift?
Pangaea
Laurasia and Gondwanaland
How continents drift
Jurassic
Cretaceous
How continents drift.
SEAFLOOR SPREADING
Is the seafloor spreading?



The magma carries the
seafloor away from
the central ridge in
both directions.
New seafloor is
continuously being
created.
Older sea floor is
pushed away from the
central ridge.
Evidence for spreading



In 1968, scientists began studying rocks on the
seafloor.
They took rock samples from the mid-ocean ridges.
They also took rock samples farther away from the
ridge.
 They
found that rocks near the mid-ocean ridge were
the youngest rocks.
 Rocks farther away from the ridge were older.
Evidence for spreading


According to Hess’s theory of seafloor spreading,
the seafloor near the ridge has formed more
recently from magma.
The older seafloor is pushed away from the ridge.
THEORY OF PLATE
TECTONICS
Plate Movements

In the 1960’s, scientists developed a new theory that
combined continental drift and seafloor spreading.
 Called the Theory of Plate Tectonics.
 Theory states – Earth’s crust and part of the
upper mantle are broken into sections.
 These sections are called plates, and move on a
plastic like layer of mantle.
 Similar to rafts on water.
Composition of Earth’s Plates

Plates are made of the crust and part of the upper
mantle.
 These
two parts combined are the lithosphere.
 This rigid layer is about 100 km thick and generally
less dense than material underneath.
 The plastic like layer below the lithosphere is called the
asthenosphere.
Earth’s Plates
Plate Boundaries

When plates move, they interact in several ways.
 They
move towards each other – Converge
 They pull apart from each other – Diverge
 They slide alongside one another – Transform
Plate Boundaries
Divergent Boundary

Two plates that are
moving apart.
 Similar
to seafloor
spreading.
Convergent Boundary



Plates moving
together.
Oceanic plates are
denser than continental
plates.
As the plate descends,
molten rock forms and
rises toward the
surface, creating
volcanoes.
Convergent Boundary


When two continental
plates move towards
each other they create
mountains.
Because both plates
are less dense than the
asthenosphere.
 The
two plates collide
and crumple up.
Transform Boundary

Two plates slide past
each other
 Move
in opposite
directions
 OR in the same
direction, just at
different rates
 When one plate slips
and moves suddenly,
an earthquake occurs.
Causes of Plate Tectonics

Many new discoveries have been made about
Earth’s crust since Wegener’s day, but one question
still remains.
 What causes the plates to move?
 Scientists now think they have a good idea.
A View of Earth
Convection Inside Earth

Soup that is cooking in a pan on the stove contains
currents caused by an unequal distribution of heat in
the pan.
 Hot,
less dense soup is force upward by the surrounding,
cooler, denser soup.
 As the hot soup reaches the surface, it cools and sinks
back down into the pan.
 This entire cycle of heating, rising, cooling and sinking
is called a convection current.
Convection Current

A version of this same process, occurring in the
mantle is thought to be the force behind plate
tectonics.
Mountains and Volcanoes

Oceanic plates are
less dense than
continental plates.
 The
pressure from the
oceanic plate under
the continental plate
pushes magma to the
surface.