Download Earth Science: Geology

Earth Science
November 12, 2005
Dr. Clodfelter
The Geologic Time Scale
The history of the
Earth is broken up
into a hierarchical set
of divisions for
describing geologic
time
The Geologic Time Scale, cont.
Highlights of recent fossil finds from
throughout geologic time (from most
ancient to most recent) are:
• Precambrian Era: the first fossil bacteria,
sponges, corals, and algae appear
• Cambrian Period: abundant invertebrate
fossils such as mollusks, crustaceans
The Geologic Time Scale, cont.
• Triassic Period: the first fossils of
primitive dinosaurs appear
• Jurassic Period: the first fossil mammals
and birds; first fossil flowering plants
appear
• Cretaceous Period: large fossil dinosaurs
appear
Quaternary
Tertiary
Cretaceous
Jurassic
Triassic
Permian
Carboniferous
Devonian
Silurian
Ordovician
Cambrian
Precambrian
Precambrian Eon
4.5 Billion to 543 Million Years Ago
• Nearly 4 thousand
million years after the
Earth began
• The first animals left
their traces
• Makes up roughly 7/8
of the Earth's history
Archaean Era
3.8 to 2.5 Billion Years Ago
• The atmosphere was very different from
what we breathe today
• The Earth's crust cooled enough that rocks
and continental plates began to form
• Life first appeared on Earth
– bacteria microfossils
Phanerozoic Eon
543 Million to
• Majority of macroscopic
organisms, fungal, plant
and animals lived
• Appearance of animals
that evolved external
skeletons – like shells –
and animals that formed
internal skeletons – like
vertebrates
Paleozoic Era
543 to 248 Million Years Ago
• In the beginning, multicelled animals
underwent a dramatic "explosion" in
diversity
• At the end, the largest mass extinction in
history wiped out approximately 90% of all
marine animal species
Paleozoic Era
543 to 248 Million Years Ago
Mesozoic Era
248 to 65 Million Years Ago
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Mesozoic means "middle animals”
Lasted 70 Million Years
Time of transition
The world-continent of Pangaea existed
The time in which life as it now exists on
Earth came together
• Important today because of the fossils and
oil left behind
Mesozoic Era
248 to 65 Million Years Ago
Divided into three time
periods:
– the Triassic (245208 Million Years Ago)
– the Jurassic (208146 Million Years Ago)
– the Cretaceous
(146-65 Million Years
Ago)
Dinosaurs in the Mesozoic Era
Dinosaurs...
– Evolved in the Triassic Period
– Became more diversified in the Jurassic
Period
– Became extinct in the late Cretaceous Period
– Fossils of some of the last dinosaurs to walk
the Earth can be found in Montana
The Cretaceous/Tertiary
Boundary in Montana
Cenozoic Era
• The most recent of
the three major
subdivisions of animal
history
– The other two are the
Paleozoic and the
Mesozoic
• Spans only about 65
million years
• Sometimes called the
“Age of Mammals”
A Continental Jigsaw Puzzle:
Putting the Pieces Together
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1911
German meteorologist
Alfred Wegener
theorized that about 300
million years ago all the
continents we know today
were joined together in a
single continent
• he named it “Pangaea”
(pronounced Pan JEE uh)
A Continental Jigsaw Puzzle:
Putting the Pieces Together, cont.
• Wegener suggested that Pangaea split
apart and its pieces began to “drift,” or
move away from each other
• He put together his own evidence, as well
as others’, to support his Theory of
Continental Drift
A Continental Jigsaw Puzzle:
Putting the Pieces Together, cont.
• At first, Wegener’s ideas were very popular
because his evidence seemed quite convincing
• Yet a number of observations still remained
unexplained
– What forces caused the continents to move?
• Due to these remaining problems, Wegener’s
theory rapidly lost support and continental drift
became “just another theory”
What are Crustal Plates?
• Earth’s crust isn’t one continuous surface
like the skin of an orange
• It is made up of gigantic pieces, like pieces
of a jigsaw puzzle
• Each piece is called a crustal plate
• Some plates form the floor of the oceans
while other carry the continents
Crustal Plates
• Molten rock around the Earth’s core heats
up the mantle above
• Currents of molten rock rise up through
the mantle like boiling water
• As each current hits the underneath of the
crustal plates, it starts to spread out
• This slowly pushes or tears the crust apart
Crustal Plates
• The plates are always on the move
• There are three basic types of plate
boundaries
– where they are sliding past each other
– where plates are separating
– where they are converging (approaching
each other)
Crustal Plates
• Spreading Center - the boundary between
separating plates
– Usually found in mid-ocean and are marked by
rugged mountain chains called mid-ocean ridges
• As plates move apart a gap continuously opens
between them
• Molten rock from the earth’s interior flows into
this gap
– New crust is continuously formed
Plates and Sea Floor Spreading
Crustal Plates
• When plates collide, the force can fold and
thrust upward to form mountains
• Or the force can push the ocean floor
downward to form a deep valley called a
trench
• Here, molten rock can break through the
seabed to form chains of islands like the
Hawaiian Islands
The Mariana Trench
The San Andreas Fault
Crustal Plate Activity
Crustal plate activity can…
• Cause earthquakes, volcanic activity, and
tsunamis
• Earthquakes are signs of the great
stresses and which affect the Earth’s crust
• Over a million earthquakes occur every
year
• Tsunamis are giant tidal waves and can
travel at 500 mph!
• Dinosaur Fossil bones have been found in
many different parts of the world
– Further supports Wegener’s single
continent theory
• The dinosaurs disappeared suddenly
– Different theories as to why
– Most widely accepted is the Big Bang Theory
• Scientists theorize that a meteor hit the
Earth at nearly the speed of light (186,000
miles per second!)
• Caused a total black out of the sun
• This meteor is believed to have caused
the Gulf of Mexico
Gulf of Mexico
• The Earth weighs about 6000 million
million million tons
• Two-thirds of the earth is covered by
water
• It would take more than 250 days to walk
around the equator
• Every year, North America and Europe separate
by 3/4ths of an inch
• Scientists predict that life on Earth will only last
50 million more years
Earth = Onion
• Crust – outermost layer, solid rock, but
very thin like skin
• Mantle – denser and heavier than the
crust, inner part of the mantle is described
as “plastic” because it is semi-liquid rock
• Core – outer part is made of molten liquid
rock that is very dense and heavy, “core”
of the core becomes solid and even more
dense
• Forms when rocks deep under the Earth’s
crust melt
• Heat from friction as the rocks rub together
can also form magma
• In places where the Earth’s crust is weak,
magma wells up on the surface as
volcanoes or lava flows
• As it cools, it becomes solid forming
new rock
• Igneous Rock – formed form cooled
magma
• Sedimentary Rock – formed by the
combining together of broken bits of other
rocks or sediments
• Metamorphic Rock – changed by
extreme pressure or heat
• Contain complex chemicals called
minerals
• Kinds of Minerals + Size of Crystals =
how the rock was Formed
• Small crystals = rapid cooling
• Large crystals = more lengthy cooling
Ring of Fire
Mount St. Helen
Krakatoa, Indonesia
• Volcanic eruption was
heard 3,000 miles
away
• Caused great tidal
wave that killed
perhaps 36,000
people
• Crystals from the
magma are smaller
because they cooled
quickly
Crater Lake, Oregon
• The caldera has filled
creating one of the
deepest lakes
• It may erupt again
• Made by the action of water and wind as
they laid down like layers of a cake
• Pressure increases and they are warmed
by the heat from deep in the Earth
• Sediment becomes a solid mass of rock
Arbuckle Mountains
Sandstone
Limestone
Decaying Plant Material
Peat
Coal
• Sea Creature dies and sinks to the sea
bed
• The soft body slowly decays creating oil
with a layer of gas sitting on top
• Skeleton is covered in layers of mud which
gradually become solid rock
• Sea bed rises above sea level
• Erosion moves rock covering fossils so
they are now exposed on land
• Radio-active carbon found in all living
things
• Begins to break down after an animal or
plant dies
• By measuring the amount of Carbon – 14
in a fossil, scientists can tell how old it is
• This is called Carbon Dating
• Layer of air surrounding the Earth
• Consists of different kinds and amounts of
gases
– Nitrogen, Oxygen, Carbon Dioxide
• Protects the Earth’s surface
– Filters out harmful radiation from the sun
– Insulates Earth and stops the sun’s heat from
escaping back into space
Three Main Layers
1) Ionosphere
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Extends about 50 miles above the surface
Rarified air
Temperature gradually rises as you move
away from the Earth
2) Stratosphere
• Extends about 30 miles above the
Earth’s surface
• Contains very little air or water vapor
• Colder than Ionosphere, but warmer than
the Troposphere
3)
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Troposphere
Bottom layer
About 10 miles thick
Contains nearly all the atmosphere’s air,
water vapor, and clouds
Temperature gradually drops until is
reaches the stratosphere
• Warm air…
– Lighter and less dense than cold air
– Rises up into the atmosphere
– Produces low pressure
• Cold air…
– Presses down heavily on the Earth’s surface
– Produces high pressure
Cirrus
– Thin, curly, and wispy
shapes
– Formed in the upper
Troposphere
– Contain ice crystals
Cumulus
– Heaped clusters like
loose cotton balls
– Have flat bases and
dome shaped tops
– Sometimes build up
into thunder clouds
Stratus
– Formed when
Cumulus clouds group
together to form a
continuous layer
– Grayer in color than
Cumulus
– Bottom of the Stratus
layer is in the lower
Troposphere
A Meteorologist Measures…
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Air pressure
Temperature
Humidity
Winds speeds and directions
Precipitation (rain, hail, snow, sleet, fog)
Cloud types and their heights
Visibility
– Name used in Asia
– Like a tornado and
hurricane combined
– Rapidly rotating tunnel
of air
– Moves over land
– Can be 300 miles in
diameter
– Winds speed at more
than 125 mph
• Similar to cyclones,
but much smaller
• Sometimes only a
mile or so across
The name given to a
cyclone which
develops in the
western Atlantic
Ocean
Infancy
Youth
Maturity
Old Age
Alps
Rocky Mountains
Arbuckle Mountains
Cumberland Mountains
Yellowstone River
Colorado River
Rio Grande
Red River