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Restless Earth
Rock Cycle
formation of different rock
This cycle is involved with three types of rock
a. Sedimentary
b. Metamorphic
c. Igneous
schematic
diagram
rock cycle
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Sedimentary Rock
a. occurs near the Earth’s surface
b. sediment settles to the bottom of the rivers, lakes,
and oceans
c. forms in layers called strata or stratification
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Sedimentary Rock Cycle
a. weather breaks down
existing rock
b. deposition
c. compaction and
cementation
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Metamorphic Rock
a rock type that has changed into another type
a. occurs 2 to 16km deep in the Earth
b. pressure is almost 4,000 times greater than
at the surface
c. temperature ranges from 1500C to 10000C
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Composition of Metamorphic rock
heat and pressure play the significant roles
in forming this type of rock
Minerals + Heat and Pressure = New mineral
New minerals formed at
different temperatures
at different depths
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Igneous Rock
formed from the cooling of magma
a. melted rock is trapped in the earth then cools
b. lava from a volcano erupts and then cools
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Three ways that rock can
become magma
a. Temperature
b. Pressure
c. Composition
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Igneous Rock formations
Two process in which magma forms rock
1. Intrusive – coarse grained rock that developed after
magma has cooled below the Earth’s surface
after weathering of Earth's surface, these intrusions are apparent
Shiprock, New Mexico
extinct volcano
dike
Devils Tower
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2. Extrusive rock – very small crystalline rock that is
formed on the Earth’s surface called lava
or under the ocean’s surface, pillow lava
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Earth’s story
Two theories on the geologic processes which points to
how the Earth’s landscape was/is formed
1. Uniformitarianism – James Hutton, 1795
developed the idea the landscape developed over long
periods of time through a variety of slow geologic
and geomorphic processes.
a. deep soil profiles were formed by the weathering
of bedrock over thousands of years
b. slow uplift and subsidence of land surfaces cause
changing topography
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2. Catastrophism - doctrine that the geological changes
in the earth's crust have been caused by the sudden
action of violent physical causes
a. biblical floods
b. asteroid impacts
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Relative dating (and I am not referring to my family tree)
uses the Principal of Superposition
a. It is based on sedimentary rocks and fossils
b. Oldest layers are at the bottom
c. Helps in the order of events
d. Produces a geologic column
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The Geologic column can have some very interesting
formations.
a. Faults - a crack in the earth's crust resulting
from the displacement of one side
with respect to the other
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b. Intrusion – molten rock that seeps into crevices
and cools
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c. Folding – rock layers bend and buckle from
internal forces
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d. Tilting – internal pressures slants the geologic
column without folding
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Unconformity – a missing part of the geologic column
mostly occurs due to:
a. deposition
b. erosion
Three types of unconformities
a. disconformity – rock layer is missing
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b. Nonconformity – sedimentary layer sits on top
igneous or metamorphic rock
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c. Angular unconformity – layer between horizontal
layer and tilted rock layer
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Absolute Dating
a process which establishes the age of an object
The process uses radioactive decay
the decay works this way:
Unstable atoms turn into stable atoms
Parent isotope – unstable isotope
Daughter isotope – stable isotope
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Radiometric dating
percentage of parent unstable isotope to
daughter stable isotope
Uses half-life of isotope to date object
64
32
Three methods of radiometric dating
a. Uranium-lead method
b. Potassium-argon method
c. Carbon-14 method
16
8
4
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The Earth may be described in two ways
1. Composition
2. Physical properties
Let’s take a look at each one
1. Composition - the Earth is composed
of three layers
a. Crust – outermost layer
b. Mantle – middle layer
c. Inner and outer cores
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There are two categories of crust
a. Continental – about 30 km thick; granite
b. Oceanic – about7 km thick; basalt
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2. Physical properties
a. Lithosphere – outermost layer (tectonic plates)
made up of 1. crust
2. upper part of mantle
b. Asthenosphere – soft part of mantle
c. Mesosphere – strong part of mantle, extends
from asthenosphere to outer core
d. Outer core – liquid layer of core
e. Inner core – solid core
6 miles
60 miles
125 miles
400 miles
Rock
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a little geology lesson!!!
Earth is made up of four layers
a. inner core - mass of iron with a temperature of
70000 F
b. outer core - electrical currents generated from
this area produce the earth's magnetic field.
c. mantle - slow moving molten rock or magma, 20000 F
d. crust - layer from 4-25 miles thick consisting of
sand and rock
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Mapping the Earth layers
a seismograph can be used to measure
the thickness of each layer
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The lithosphere is made up of tectonic plates; these
are plates that float on the asthenosphere
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Cross section of a tectonic plate
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Continental Drift
Wegener, Alfred – 1880 - 1930
theory that all of the worlds land masses were
at one time together !!!!!
called the land mass Pangaea – about 245 million years ago
Evidence:
a. continents fit together like a puzzle
b. identical fossils on one continent are found
on another
e.g. plants on S. America, Africa, Antarctica
and Australia
c. glaciers
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Are the continents on the move???
Yes, about 2 to 3 inches per year
How you ask...
Sea-floor Spreading!!!
As the continents move
apart the mid-ocean ridge
pulls apart and molten
rock fills the gap
That is how the geologists determine the age of the ocean floor
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As the magma makes new sea floor, the magnetic poles
actually change direction
At irregular intervals, averaging about 200-thousand years,
the Earth's magnetic field reverses. The end of a compass
needle that today points to the north will instead point to
the south after the next reversal.
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Theory of Tectonic Plates
Two possible answers for tectonic plate shift
a. gravity
b. heat
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