Geology - The study of rocks and the
solid part of the Earth.
A good website for info and can be found here.
Supporting files for this material can be found here.
1912 - Alfred Wegener
Based on three
- The shape of the
continents seem to fit together like puzzle pieces.
- There are
similar plants and animals on different continents.
- There is
evidence of glaciers in warm places (like Australia) and warm environments in
cold places (like Antarctica).
The Theory of Continental Drift has
- All continents were once joined together in a
supercontinent called "Pangaea".
- The continents have drifted to their current
positions over millions of years.
- The continents are still moving.
1965 - John Tuzo Wilson
The Theory of Plate Tectonics states...
- The Earth's crust is divided into pieces called tectonic plates.
- As the plates move, they carry the continents with them.
The are three main types of plate boundaries:
- Divergent Plate Boundaries
- Plates move apart.
- Magma from the mantle comes up, is cooled by ocean water, turns to rock, and
pushes the plates apart. (New plate is formed here.)
- ex. - Mid-Ocean Ridge (Mid-Atlantic Ridge)
- Convergent Plate Boundaries
- Plates come together to form mountains.
- Happens when two continental plates collide.
- ex. - Himalaya Mountains (India & Asia)
- One plate goes under another: subduction.
- Ocean plate goes under a continental plate.
- ex. - Japan, Andes Mountains, Alaska
- Transform Plate Boundaries
- Plates move along side each other.
- ex. - San Andreas Fault (California).
- A break in the Earth's crust where the rocks on either side
Focus - The origin of an earthquake. This is the
place inside the crust where the rocks actually break and
Epicenter - The place on the surface that is directly
above the focus.
Seismic Waves are vibrations in the
ground that are caused by an earthquake. There are three types:
Primary (P) Waves
These are the fastest type of
seismic wave. P-waves represent the back and forth motion of the
(On this site,
look at the longitudinal wave.)
Secondary (S) Waves
S-waves represent the up and down
motion of the rock.
(On this site,
look at the transverse wave.)
These are the slowest, but most destructive type of
seismic wave. L-waves cause the ground to move like the surface
of the ocean.
(On this site,
look at the Rayleigh surface waves.)
seismograph is a device that measures the strength of
earthquake waves. A diagram and explanation of a simple seismograph are
attached here. A short video on how a seismograph works can be found here.
listing the strongest earthquakes since 1900 can be found here.
An explanation of the Richter Scale - and other earthquake scales - can be found here.
volcano is a break in the Earth's crust where lava comes out.
There are three main parts to a volcano:
- Vent - This is the
crack in the crust where magma comes up from the
- Crater - This is the opening, at the top of the
vent, where the lava comes out.
- Cone - This is the
"mountain" that is built up around the volcano's
Magma - Molten rock below the surface of the
Lava - Molten rock on the surface of the
Volcanic projectiles are objects that are thrown
through the air by a volcano. There are three main types. Ash
and dust are the smallest type, only a few millimeters across.
Cinders are larger - up to several centimeters across.
Lava bombs are the largest. They can be up to a meter across,
and whistle as they fall through the air.
There are three major types of
that Shape the Crust
- Cinder Cones are volcanoes which tend to erupt
violently, throwing out a lot of ash and cinders. This builds up a steep cone
- Shield Volcanoes tend to erupt more gently,
with lava flowing out without throwing projectiles. This builds up a gently
sloping cone, made of layer upon layer of hardened lava rock.
- Composite Volcanoes alternate between erupting violently and quietly
seeping. As a result, their cones are made of alternating layers of ash/cinders
and lava rock.
Diastrophism - The
movement of the solid rock in the Earth's crust.
- The balance of how the crust floats on the mantle.
A good way
to think about isostasy is to consider how a boat floats on water. When the
boat is empty, it sits pretty high in the water. When people start getting into
the boat, it rides lower and lower in the water. The crust is the same way.
The thinner oceanic crust does not sink as far into the mantle as the thicker
Fault - A break in the crust where
the rock on either side moves.
Joint - A break in the crust
where the rock does not move.
Fold - A place in the crust
where the rock bends, but does not break.Building
- Fault-Block Mountains are formed
when large "blocks" of the crust get tipped over, forming steep and jagged
- Syncline & Anticline are places where the
crust is folded, making more gently sloping mountains. (Syncline folds down;
anticline folds up.)
- Dome Mountains are formed when magma
from the mantle pushes up the rock layers to form a dome-shaped
Plateaus are large, raised
areas of flat land. There are three main ways that they are formed...
- when water carves away the land, plateaus are left behind.
- (i.e. - the
area around the Grand Canyon.)
- when lava builds up layers of rock across
- (i.e. - the Columbian Plateau.)
- when the surrounding
Weathering is the breaking of
rock into smaller bits. There are two main types of weathering:
Physical Weathering is the breaking of rock into
pieces of the same material.
Weathering is the breaking of rock into different
Erosion occurs when the bits of rock are
of Physical Weathering
Water gets into cracks in the rock, freezes and expands,
cracks open wider.
- This is when the
outer layers of rock peel or flake off.
When rock is heated, the minerals in it expand at different
This puts stress on the rock, which can cause it to
- As plant roots grow in cracks in the rock, they
open wider and wider.
Examples of Chemical
- Some minerals
dissolve in water, changing the composition of
- Oxygen can combine with some materials to make
substances. This is called oxidation.
- An example of this
is rust: a compound that is made up of
both iron and oxygen.
- Carbon dioxide can be
absorbed by rain to make carbonic
acid - a weak acid that can dissolve
- Some plants secrete acids
through their roots, which dissolves
certain minerals and weakens the
Formation of Soil
Horizon - any separate layer of soil.
C-Horizon - partly weathered rock.
A-Horizon - topsoil - made of humus (decayed plants and animals).
B-Horizon - subsoil - formed when water washes down tiny particles and dissolved minerals from the topsoil.
Erosion can be caused by...
Sediments - Particles dropped off by water or wind.
- Silt - Smallest
- Gravel - Largest
Runoff Water - Water flowing over the surface of the land.
The faster the water moves, the more/larger the sediment it can carry.
- Tributaries - Smaller streams/rivers that flow into larger streams/rivers.
- Watershed - The area of land that drains into a river/lake.
- Delta - A deposit formed at the mouth of a river.
- Sediment in a delta is sorted by size as the water slows down.
Examples of Erosion Caused by
- A landslide is the sudden downhill
movement of large amounts of loose rock and soil.
- Talus - pile of broken rock at the bottom of a cliff or slope.
- A slump is
the sudden downhill movement of a block of rock and soil.
- The slow downhill
movement of rock and soil is called
- Precipitation, groundwater and runoff can cause erosion.
Rocks & Minerals
Parts of the Earth
Atmosphere - The layer of air that surrounds the Earth.
Hydrosphere - All of the water on the surface of the
- Lithosphere - The solid part of the Earth's crust
- Biosphere - All of the living things on the
surface of the Earth.
- Cryosphere - All of the ice on the
surface of the Earth.
Minerals are solid,
naturally-forming substances that are found in the Earth and always have the
same properties. See the attached PowerPoint on minerals
Rocks are solid pieces of the Earth's
crust. They are made up of minerals. There are 3 main types of rock:
Igneous Rock - Sedimentary Rock - Metamorphic Rock
Rock is formed when magma/lava cools and hardens. The word "igneous" means
"coming from fire." There are 2 types of igneous rock:
Intrusive Rock is formed from magma inside the
crust. It cools slowly and tends to form larger crystals.
example is granite.
Rock is formed from lava on the Earth's surface.
quicker than intrusive rock and tends to form smaller
crystals (or no
crystals). Examples are obsidian and pumice.
As a general
rule, the slower the lava/magma cools,
the bigger the crystals will be. Intrusive igneous rock can form
structures inside the crust. A dike is a layer of igneous rock
that cuts across other rock layers. A sill is a layer of
igneous rock that runs parallel to other rock layers. A
batholith is a huge area of underground igneous rock.
Batholiths often form the cores of mountains.
Sedimentary Rock is made of sediments (particles dropped off
by water or wind). There are 3 types of sedimentary rock:
Clastic (Cemented/Compacted) Rock
when sediments get crushed into rock. The type of rock
forms depends on the type of sediment that gets
- Silt forms shale.
- Sand forms
- Gravel forms
Sediments form when water evaporates,
behind. (This is like when you swim in the
ocean - afterwards, the
water evaporates and leaves a layer
of salt on you.) Examples of
chemical sediments include
gypsum and rock
Sediments form from the remains of living things.
example, peat moss that is buried for thousands of years
coal. The shells of ocean animals can gradually be
As a general rule, the faster water moves, the bigger the
particles that it can carry. This means that the fastest streams and
rivers will carry away the sand and silt, leaving rocks and gravel on their
bottoms. As the water slows down, it will drop off the sand - this creates a
sandy bottom. Really slow water will drop off silt, creating a silty/muddy
Metamorphic Rock forms when other types of rocks
are changed by heat and pressure. Examples include:
- gneiss (changed
- schist (changed from mica)
- slate (changed from
- quartzite (changed from sandstone)
- marble (changed from
The Rock Cycle is the endless process by
which rocks are formed, destroyed, and formed again. This cycle begins with
magma, which cools into igneous rock.
- melt back into magma,
- weather into sediments, which
form sedimentary rock,
- change, with heat and pressure, into
Sedimentary Rock can...
- weather into sediments, which form
other sedimentary rock,
- change, with heat and pressure, into
Metamorphic Rock can...
- weather into sediments, which form sedimentary
The Rock Record
The Earth is about 4.6
billion years old. To think about this, imagine that we stretch a piece of
string from the windows in the middle school Resource Room to the windows in Mr.
Byrne's classroom. This string represents the Earth's history from the very
beginning to today. Each centimeter (about the length of the word "each" at the
beginning of this sentence) would be equal to about 1 million years. All of
human history would be within about the last 3
Uniformitarianism is the idea that the same
processes are happening on the Earth now as have happened in the past. Some
examples of processes that have happened throughout Earth's history include:
weathering, erosion, the Water Cycle, and the Rock
Absolute Age means how old something is in
years. Relative Age means how old something is compared to
something else (older or younger). Geologists look for certain clues to figure
out a rock layer's age.
The Law of Superposition states
that, if you're looking at a set of rock layers, the layers on top will tend to
be younger than the layers on the bottom. This is because the layers on the
bottom formed first, with later layers forming on top of
Crosscutting is the idea that a fault or
magma-flow that cuts across layers of rock must be younger than the rock they
An unconformity is the boundary between
younger layers of rock and older layers that have been eroded.
fossil is aany preserved part, trace, or entire remains of an
organism that lived long ago. There are several ways in which fossils may be
1. Ice forms fossils by freezing the organism, so
that it does not decay.
2. Amber is fossilized tree sap.
Most of the insect fossils that we
have today are from amber.
Tar is a type of oily sludge. Animals that wander into tar
can get stuck and pulled down into the tar, where their
4. Burial means that the
organism is buried in the ground.
Because oxygen can't get to it, the
process of decay is slowed
down or even halted. The hard parts of the
organism, like the
bones or shells, get preserved.
Petrification happens when an organism is buried.
that is in the ground can dissolve the organic bits of
organism and replace them with minerals. Over time, the
entire organism is "turned to stone" in this way.
and Casts also form when an organism is buried. The
mud that the organism is buried in gets compressed into rock,
the organism decays and is washed out by
groundwater. This leaves an
imprint, which is called a mold.
If the mold gets
filled in with minerals, this model of the
organism is called a
The Age of Rocks
bed is a rock layer that is easily recognized and is found over a large
area. Once geologists identify a key bed, they can use it as a guide to study
the layers above and below it.
Index fossils are the
remains of plants or animals that only lived during a short part of the Earth's
history. If you know when a certain critter lived, then you know how old the
rocks are that contain its fossilized remains.
Key beds and index fossils
are used to create a geologic column. This is a model that
shows the order that rock layers formed in.
decay is there process by which elements break down into simpler
elements over a long period of time. The time it takes for half of a sample of
a given element to break down is called its half-life. (See
the attached PowerPoint.) Some examples of elements' half-lives are:
Uranium decays into Lead. Half-life: 4.5 billion years.
- Potassium decays
into Argon. Half-life: 1.3 billion years.
- Carbon-14 decays into
Carbon-12. Half-life: 5,800 years.
The Earth is about
4.6 billion years old. To study its history, we divide this time into
We used to separate
Earth's history into three eras: the Paleozoic, the Mesozoic, and the Cenozoic.
Everything that happened before the Paleozoic Era was lumped together in what we
call "Precambrian Time", because we did not have the knowledge of what the Earth
was like during this period to be able to divide it into eras. (Precambrian
Time is much longer than the three eras combined.)
Now that we are
able to separate Precambrian Time into Eras, we sometimes refer to the combined
Paleozoic/Mesozoic/Cenozoic time as the Phanerozoic Eon.
- Plate Tectonics & Continental Drift
- The Rock Cycle
- The Rock Cycle Song - Pretty good overview of the Rock Cycle. ("Life Is a Highway" by Rascall Flats)
- We Will Rock You - Song covering the three rock types. ("We Will Rock You" by Queen)
- Formed This Way - Fast-paced song, covers the three rock types. ("Born This Way" by Lady Gaga)
- Geologic Time
- Here Is Today - A visualization of "today" in terms of the age of the Earth. Very cool. Sent to me by Abby R (Class of 2019).
Supporting files for this material can be found here.