Transcript What is a Rock?

Our Dynamic Earth
Earth as a System
• The Earth is an integrated system that consists of rock, air,
water, and living things that all interact with each other.
• Scientists divided this system into four parts:
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The Geosphere (rock)
The Atmosphere (air)
The Hydrosphere (water)
The Biosphere (living things)
Earth’s Interior
• Scientists use seismic
waves to learn about
Earth’s interior.
• Seismic waves are the
same waves that
travel through Earth’s
interior during and
earthquake.
• A seismic wave is
altered by the nature of
the material through
which it travels.
Layers of the Earth
• Scientists divide the
Earth into three
layers:
– The crust
– The mantle
– The core
• These layers are
made up of
progressively denser
material toward the
center of the Earth.
Processes and Forces that
Affect the Lithosphere
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Rock Cycle
Weathering
Erosion
Soil Formation
Plate Tectonics
Earthquakes
Volcanoes
Humans
Rockin’ the Rock Cycle
Rock Cycle
• Rocks are continually
changed by many
processes, such as
weathering, erosion,
compaction,
cementation,
melting, and cooling
• Rocks can change to
and from the three
types through the
rock cycle.
What is a Rock?
• Naturally-occurring mixtures of minerals, mineraloids,
glass or organic matter.
• Rocks are divided into 3 groups based on how they
were formed:
• IGNEOUS
• SEDIMENTARY
• METAMORPHIC
Igneous Rock
• Igneous rock is made when magma cools
and crystallizes. (Igneous means “from fire
or heat”)
Type of
Igneous Rock
Where does
it Form?
How does it
Cool?
What Size
Grains does
it have?
Example
Intrusive
Inside
Earth
Outside
Earth
Slowly
Large
(Course)
Small
(Fine) or
Glassy
(Very
Fine)
Granite
Extrusive
Quickly
Basalt
Obsidian
Examples of Igneous Rock
Granite: Large/Course Grains
Basalt: Small/Fine Grains
Obsidian: Glassy/Very Fine
Grains
What happens to the Igneous Rock?
1. It can be weathered
and eroded and
turned into small
pieces, called
sediment, which can
then be turned into a
sedimentary rock.
2. It can be put under
high heat or
pressure and form a
metamorphic rock.
3. Could melt and
become magma again
Sedimentary Rock
1. Rock is weathered and forms
sediments
– Sediments: smaller pieces of rock
• Examples: Gravel, Sand, Mud, Soil
Sedimentary Rock
2. Erosion
– The process by which weathered rock and
soil particles are moved from place to place
by wind, water, gravity, glaciers, etc.
3. Deposition
– The process by which weathered sediments
are laid down in a new location creating new
landforms through “bedding”.
3. Deposition – Types of Bedding
1. Bedding – oldest sediments on the
bottom, youngest sediments on top
2. Graded Bedding – biggest sediments
on bottom, smallest on top (happens in
water)
3. Cross Bedding – sediments are laid at
an angle (ex: sand dunes)
Sedimentary Rock
4. Lithification - Sediments must be
buried, compacted, cemented together
to make a sedimentary rock.
• Examples of Sedimentary Rock:
Coal
Sandstone
Shale
What happens to Sedimentary Rock?
1. Could weather and
erode to become
sediments which
cement and compact
to form sedimentary
rock
2. It can be put under
high heat or
pressure and form a
metamorphic rock.
3. Could melt to form
magma which cools
and hardens to form
igneous rocks.
Metamorphic Rock
• Formed from
existing rocks.
• Are created by
intense heat or
intense pressure.
• Can be foliated =
looks like it has
layers (made from
pressure)
• Can be nonfoliated = does not
look like it has
layers (made from
heat)
Limestone (Sedimentary)  Marble
Shale (Sedimentary)  Slate
Granite (Igneous)  Gneiss
What happens to Metamorphic Rock?
1. Could weather and
erode to become
sediments that
cement and
compact to form
sedimentary rocks
2. Could melt to form
magma which cools
and hardens to
form igneous rocks
How are rocks redistributed?
• The core, mantle, & crust are one giant
rock recycling machine changing the
lithosphere.
Weathering
Weathering
Weathering is the breaking down of
rocks and other materials on the
earth’s surface
Physical Weathering
Breaks rock into smaller pieces without
changing the overall composition.
Examples- Biological Activity (tree roots and
animals burrowing), Frost Wedging (water
freezing inside cracks of rocks causing them
to expand and break), Gravity
Chemical Weathering
Chemical reactions that change the overall
composition of the rock.
Examples- Water (most important agent),
Acid Rain on gravestones (dissolves
minerals), Oxidation
Factors that determine the rate of weathering:
o Composition
Granite more resistant than marble.
o Physical conditions of rock
 Cracks, holes, crevices – easier weathering
 Solid, unbroken – more weather resistant
o Topography: the position of the rock
o Air pollution
o Exposure time
o Surface area exposed
o Climate
o Cold Climates– mechanical weathering breaks
down rocks rapidly
 Warm, wet climates – chemical weathering
breaks down rocks rapidly
Mechanical and chemical weathering work together
Erosion
5 Agents of Erosion
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Gravity
Glaciers
Wind
Water
Ocean Waves
Soil formation starts with…
• Weathering
• Erosion
• Deposition
Followed by…
• Some living
organisms such as
bacteria, fungi
and insects.
• They die, decay
and add nutrients
to the soil.
So Basically…
Soil is a layer at the surface of the
earth composed of a mixture of
weathered rock, organic matter,
mineral fragments, water, and air
which is capable of supporting the
growth of plants impacting the
lithosphere.
Plate Tectonics
What observations can you make
about the shape of the
continents?
What’s interesting? Just 200
million years ago, this is what the
world looked like:
Plate Tectonics
 Tectonic plates - blocks of lithosphere
that consist of the crust and the rigid,
outermost part of the mantle and glide
across the underlying asthenosphere.
 The continents are located on tectonic
plates and move around with them.
 The major tectonic plates include the
Pacific, North America, South America,
Africa, Eurasian, and Antarctic plates
Plate Boundaries
• Much of the
geological activity at
the surface of the
Earth takes place at
the boundaries
between tectonic
plates.
• Tectonic plates may
separate, collide, or
slip past one
another.
Plate Boundaries
Divergent Boundary:
Plate Boundaries
Divergent Boundary:
 Plates are moving away
from each other
 Midocean ridges are
created and new ocean
floor plates are created
Rift Valleys
Leif the Lucky Bridge Bridge between continents in Reykjanes
peninsula, southwest Iceland across the Alfagja rift valley, the
boundary of the Eurasian and North American continental tectonic
plates.
Plate Boundaries
Convergent Boundary:
 plates are moving toward
each other and are
colliding (3 types)
Convergent Boundaries
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Create
subduction
zones, trenches
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Create near
coast volcanoes
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Island arcs are
created
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Mountain ranges
are created
– (example:
Himalayan
Mountains)
Himalayan Mountains
Plate Boundaries
Transform Fault Boundary
 Plates are neither moving
toward nor away from each
other, they are moving past
one another.
Transform Fault Boundary
 The plates may move in opposite
directions or in the same
directions but at different rates
and frequent earthquakes are
created (example: San Andreas
Fault)
San Andreas Fault
So is the Earth getting bigger?
o No
o Plates are destroyed as fast as they
are created (2 ways)
o Plates may be subducted and melted
or may push be pushed upward to
form mountains
What types of forces are
created?
Tensional Force:
 stretching or pulling
 Creates a normal fault
What types of forces are
created?
Compressional Force:
 force pushing something together
 Creates a reverse fault
What types of forces are
created?
Shear or Transversal Force:
 a system of forces that
operates against a body
from different sides
 Creates a strike-slip fault
Earthquakes
• A fault is a break in the Earth’s crust along
which blocks of the crust slide relative to one
another.
• When rocks that are under stress suddenly
break along a fault, a series of ground
vibrations, known as earthquakes, is set off.
• Earthquakes are occurring all the time. Many
are so small that we cannot feel them, but
some are enormous movements of the Earth’s
crust that cause widespread damage.
Earthquakes
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The actual place
underground where the
earthquake starts and
rocks break producing
vibrations is called the
focus.
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The place on the surface
directly above the focus
is called the epicenter
Seismic Waves
Originate at the focus and travel
outward in all directions
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Three Types: P wave, S wave, surface waves
Foreshocks: small earthquakes that
come before a major earthquake
Aftershocks: Are adjustments in the
crust after in earthquake.
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Smaller than main earthquake, but can cause
as much or more damage. They can continue
for weeks to months.
How do we Measure
Earthquakes?
Earthquake waves are recorded by a
seismograph and the recording of waves
on paper is called seismogram
Measuring Earthquakes
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Locating the epicenter
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Lag time between the arrival of the P wave and the S wave
to the seismograph station is converted to a distance
A circle with a radius that equals the distance is drawn
around the station.
Three stations can narrow down the location to where the
circles intersect
Locating the focus: the lag-time of the
surface wave will determine the depth of the
focus
Measuring Earthquakes
Where do Earthquakes Occur?
• The majority of earthquakes take place at or
near tectonic plate boundaries because of the
enormous stresses that are generated when
tectonic plates separate, collide or slip past
each other.
• Over the past 15 million to 20 million years,
large numbers of earthquakes have occurred
along the San Andreas fault in California,
where parts of the North America plate and
the Pacific plate are slipping past one another.
Where do Earthquakes Occur?
Earthquake Dangers
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Landslides
Avalanches
Volcanoes
 A volcano is a mountain built from magma, or
melted rock, that rises from the Earth’s
interior to the surface, and can occur on land
or in the sea.
 Volcanoes are often located near tectonic
plate boundaries where plates are either
colliding or separating from one another.
 The majority of the world’s active volcanoes
on land are located along tectonic plate
boundaries that surround the Pacific Ocean.
Volcanoes: The Ring of Fire
The Birth of a volcano
What comes out of volcanoes?
•Lava
•Tephra
•Gases
Tephra
• Basically, rock fragments
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Also known as pyroclastic rock
fragments.
There are many different possible
sizes, from very small (volcanic ash or
dust to much larger rocks (called
volcanic bombs)
GASES
water vapor, carbon dioxide,
nitrogen, sulfur dioxide,
hydrogen sulfide, chlorine
Types of
Volcanic Eruptions
Two factors determine the type of eruption:
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Amount of water vapor & other
gases in the magma
The chemical composition of
the magma
Explosive Eruptions
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Trapped gases
under high pressure
will violently explode
Has granitic magma
The high water
content of the
magma produces
more water vapor
which when mixed in
granitic magma
produces explosive
eruptions
The eruption of Mt. St. Helens in 1980
Quiet Eruptions
• Low Pressure gas
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Has basaltic magma
(is more fluid and will
flow instead of
explode)
…and has low water
content
Examples: Hawaii
A typical Hawaiian Eruption
Types of volcanoes
Local Effect of Volcanic
Eruptions
 Clouds of host ash, dust, and gases can flow
down the slope of a volcano at speeds of up to
200 km/hr and sear everything in their path.
 During and eruption, volcanic ash can mix with
water and produce mudflow (lahar) that runs
downhill.
 In addition, ash that falls to the ground can
cause buildings to collapse under its weight,
bury crops, damage the engines of vehicles,
and cause breathing difficulties.
Global Effect of Volcanic
Eruptions
• Major volcanic eruptions can change Earth’s
climate for several years.
• In large eruptions, clouds of volcanic ash and
sulfur rich gases may reach the upper
atmosphere, and spread across the planet
reducing the amount of sunlight that reaches
the Earth’s surface.
• The reduction in sunlight can cause a drop in
the average global surface temperature.
Human Impact on the
Lithosphere
Urbanization
• Destroying natural areas
can reduce the beauty
of an area and have a
potential economic
impact.
• Rapid development can
result in very high levels
of erosion and
sedimentation in river
channels.
• Pollution of soils is
possible by leaking gas
tanks and other
chemicals.
Agriculture
• Agriculture takes space.
• Use of chemical
pesticides, insecticides
and fertilizers can
contaminate soil and
affect soil fertility.
– Organic fertilizers
are better.
• Planting the same crop
over and over can strip
vital minerals out of the
soil.
– Crop rotation can
help.
Deforestation
• Cutting down all the trees in an area
loosens the soil and makes it very easy
for extreme erosion to occur.
• One solution is replanting and a system
of harvesting that thins out the area.
Overgrazing
• Overgrazing is the removal of excessive
amounts of plant growth by animals in
one area. This accelerates erosion and
strips away topsoil, resulting in no plants
able to grow.
• It is best to rotate animals among
pastures.
Mining
•Strip
Underground
Mining mining requires digging out large areas,
increasing the risk for sinkholes and cave ins.
• Strip mining destroys the environment.
• Mine operators must reclaim the land after mining is
finished (put the land back together and restore it to
its original condition).
Harvesting Peat
• Peat is an accumulation of partially decayed
vegetation. Eventually, peat can turn into coal and
be burned for fuel.
• Advantages
low sulphur content
minimal mercury content
low ash content energy
values equivalent to coal, less expensive than oil and
natural gas and competitive with other biofuels
– minor engineering retrofit needed when substituted
for, or blended with, coal
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• Since peat forms nearer to the surface, it requires
less digging.
Drilling for Oil and Natural Gas
• Oil and Natural Gas
are nonrenewable
resources.
• Drilling can cause
the lithosphere to
be disturbed and
can cause
earthquakes.
• Soil and
groundwater can
also be
contaminated.
– Fracking is a hot
political topic.
Human Activity and the Coast
• As more and more people retire, there is more
development on our coast.
• Removal of vegetation at the coast can cause
serious erosion.
• Man made erosion control, like sandbags, can
make erosion worse downshore.
• Erosion causes houses to be condemned and
potentially fall into the ocean.