Most Abundant Elements
in the Earth’s Crust
1
oxygen
O
2
silicon
Si
3
aluminium
Al
4
iron
Fe
5
calcium
Ca
6
sodium
Na
7
potassium
K
8
magnesium
Mg
Theory of Pangaea
Future
Natural and Unnatural Forces
• Present day Earth is a result of billions of years
of changes caused by natural and unnatural
forces.
• Natural: plate tectonics, volcanic action, wind,
water , etc.
• Unnatural: pollution, soil degradation, etc.
Earth’s Age
• Earth is currently theorized to be 4.5 to 4.7
billion years old
How long?
• Do you ever wonder how
long it took for certain
land forms to form?
• Scientist believe that the
Earth as we know it began
to take shape between 66
and 144 million years ago
(Cretaceous Period)
Earth’s Layers (General)
• Crust: Outermost
Layer. It is thin and
rigid
• Mantle: Dense, hot,
semi-solid rock
• Core: solid inner and
liquid outer
Plate Tectonic Theory
The two big forces working to
change the face of the Earth are:
1. Weathering and erosion.
2. Plate tectonics
Plate Tectonic Theory
• Plate tectonics is a relatively new theory that has
revolutionized the way geologists think about the
Earth.
• Plate: Large slab of solid rock
• Tectonics: from the Greek root “to build”
• Plate tectonics is a combination of two ideas,
continental drift and sea-floor spreading.
Tectonic Plates
• According to the theory, the surface of the
Earth is broken into large plates.
Earth’s Interior
The lithosphere is the rigid, upper part of the
mantle and all of the crust
It is broken into 30 “plates” which vary greatly in
size and shape.
The lithosphere floats on the asthenosphere
which is the flowing part of the upper mantle.
INSIDE THE EARTH
Three main layers:
1. Crust
Lithosphere
(crust and upper mantle)
2. Mantle
3. Core
Outer
Inner
Asthenosphere
(plastic layer that the
the lithosphere floats
upon)
Historical Theories
1596Abraham Ortelius (April 14,
1527 – June 28, 1598) was a
Flemish cartographer
(map maker) and
geographer.
Proposed Continental Drift
Ortelius is believed to be the first person to
imagine that some continents were joined
together before drifting to their present
positions.
Ortelius was the first to see that
the shape of the coasts of South
America and Africa were similar,
and to propose continental drift
due to earthquakes and floods.
Nicolaus Steno
1636-1686
NicolausSteno-1669-observed the
changes in a sequence of rock
layers in the mountains of Italy.
•Steno's observations became
known as the Law of
Superposition
Danish Anatomist and
Geologist
Law of Superposition
– in a
sequence of
sedimentary rock layers,
each layer of rock is older
than the layer above it
and younger than the rock
layer below it.
Youngest
rock layer
Oldest
rock layer
James Hutton
1785James Hutton (1726-1797)
was a Scottish
geologist.
In 1785 he presented his
uniformitarian
principle to the Royal
Society of Edinburgh.
Uniformitarian principle
“The present is the key to the past”
• suggests that catastrophic processes were not
responsible for the landforms that existed on
the Earth's surface.
• This idea was opposed to the ideas of that
time period which were based on a biblical
interpretation of the history of the Earth.
Uniformitarianism
• means “the same throughout”
• Scientists believed that the rates of all
geologic processes had been the same
throughout time.
The theory of uniformitarianism suggested that
the landscape developed over long periods of
time through a variety of slow geologic and
geomorphic processes.
Canyons, like The Grand Canyon in Arizona, show how geologic
processes such as weathering and erosion happen slowly over
time.
Alfred Wegener
Alfred Wegener (1880-1930)
• German geophysicist
• Professor of meteorology
and geophysics at the
University of Marburg
• Studied fossils on different
continents
1912- Supercontinent Theory
• around 200 million years ago, the supercontinent
Pangaea began to split apart .
• Pangaea comes from the Greek “all the Earth”
Wegener's theory was
based in part on what
appeared to him to be the
remarkable fit of the South
American and African
continents, first noted by
Abraham Ortelius three
centuries earlier.
Fossil Evidence
• Wegener was also intrigued by the occurrences of
unusual geologic structures and of plant and animal
fossils found on the matching coastlines of South
America and Africa, which are now widely separated
by the Atlantic Ocean.
• He reasoned that it was physically impossible for most
of these organisms to have swum or have been
transported across the vast oceans. To him, the
presence of identical fossil species along the coastal
parts of Africa and South America was the most
compelling evidence that the two continents were
once joined.
Pangaea
Continental
Drift
225 million years agoSupercontinent
Pangaea
Over millennia,
continents drifted
apart.
Present Day:
7 continents which are
continuing to drift
(separate) at a rate of
about 10 cm per year.
A Theory Contended
• The theory of continental drift would become
the spark that ignited a new way of viewing
the Earth. But at the time Wegener introduced
his theory, the scientific community firmly
believed the continents and oceans to be
permanent features on the Earth's surface.
• Wegener’s proposal was not well received,
even though it seemed to agree with the
scientific information available at the time.
The Fatal Weakness
• A fatal weakness in Wegener's theory was that
it could not satisfactorily answer the most
fundamental question raised by critics of his
time:
What kind of forces could be strong
enough to move such large masses
of solid rock over such great
distances?
Arthur Holmes Lived 1890–1965
British Geologist
• 1929 - Convection Currents
Theory – about the time
Wegener's ideas began to be
dismissed for lack of a
mechanism of movement,
Holmes elaborated on the idea
that the mantle undergoes
thermal convection
Thermal Convection in the Mantle
• As magma is heated, it tends to rise, then cools and
sinks again. This repeated heating and cooling
results in a current which may be enough to cause
continents to move.
Convection Currents
Convection Conveyor Belt
• Arthur Holmes compared this thermal
convection to a conveyor belt. The
pressure from the upwelling of magma
could break apart a continent and then
force the broken continent in opposite
directions carried by the convection
currents. This idea received very little
attention at the time.
What We Know Today
• Even though the theory of continental drift
was proposed in 1912 by Alfred Wegener, the
idea of moving continents wasn't generally
accepted until the early 1960s.
• That's when Wegener's theory was
resurrected by Harry Hess, Robert Dietz, Fred
Vine, and Drummond Matthews
Forces that Shape the Earth
• Geologists now understand the forces that
cause tectonic plates to move.
• The force that causes plates to move is called
convection.
• This convection force occurs in the
asthenosphere of the mantle
Convection Currents
• The lithospheric plates are
thought to be moved around
by circulating motions.
• This process is similar to what
you see in a lava lamp.
– The material in the lamp is
heated by the bulb. The material
then rises and is replaced by the
cooler material that sinks to the
bottom.
– This causes circulating movement
Convection in the Earth
convection currents
in the mantle move
tectonic plates as the
plastic-like
asthenosphere
circulates due to the
heat present in the
core.
The large scale circulations (motions) in the asthenosphere
move the lithospheric plates on the surface of the Earth
leading to the continental drift observed today.
Harry Hess
Lived 1906–1969 American Geologist
• 1962 - Sea Floor Spreading Theory
– idea that the seafloor itself moves
and carries continents with it, as it
expands from a central point
• caused by convection currents in the
molten, very weak upper mantle, or
asthenosphere.
Sea Floor Spreading
• molten magma from beneath
the earth's crust could ooze up
between the plates in the rift
in the ocean floor.
• As the hot magma cooled in
the ocean water, it would
expand and push the plates
beside it.
Mid Atlantic Ridge
• North and South America
would move to the west and
Eurasia and Africa would move
to the east.
• The Atlantic Ocean would get
wider, but the coastlines of the
landmasses would not change
dramatically.
Dan McKenzie
Lives 1942– English Geophysicist
• 1968 - Theory of Plate Tectonics – is a
combination of two earlier ideas: continental
drift and sea-floor spreading.
Plate Tectonics
• Earth's outermost layer, the lithosphere, is
broken into 7 large, rigid pieces called plates.
• Several minor plates also exist.
• The plates are all moving in different
directions and at different speeds, from 2 cm
to 10 cm per year in relationship to each
other.
Main Features of Plate Tectonics
• The Earth's surface is covered by a series of crustal
plates.
• The ocean floors are continually moving, spreading
from the center, sinking at the edges, and being
regenerated.
• Convection currents beneath the plates move the
crustal plates in different directions.
• The source of heat driving the convection currents
is from radioactivity deep in the Earth’s mantle.
Inside the Earth
– The Earth is a dynamic or constantly changing planet. The
thin, fragile plates slide very slowly on the mantle's upper
layer. This sliding of the plates is caused by the mantle's
convection currents slowly turning over and over. This
overturn is like a conveyor belt that moves the plates of
the crust.
– These plates are in constant motion causing earthquakes,
mountain building, volcanism, the production of "new"
crust and the destruction of "old" crust.
Plate tectonics
• This theory is fairly young (about 30 yrs old)
• Plate tectonics has answered a lot of questions such
as why earthquakes and volcanoes eruptions occur in
specific areas around the world and how great
mountain ranges such as the Himalayas were
formed!!
• Answer: The Indian plate crashed into the Eurasian
plate with such speed and force that it created the
tallest mountain range on Earth, the Himalayas
Plate Tectonic Theory Timeline
• Design your timeline.
• Make sure you write the actual date and name
of Scientist.
• Include the name of the theory or hypothesis.
Plate Boundaries
• As plates move, the boundaries interact
with one another.
– Types of Plate Boundaries:
• 1. Divergent
• 2. Convergent
• 3. Transform
Plate Boundaries
Plate Boundaries
Hawaiian Islands