Earth History Benchmark Study Guide 2014
Sedimentary Rocks
Sedimentary Rocks: Class of rocks that are
formed when a metamorphic rock or igneous
rock undergoes weathering and erosion and
is broken into small pieces and deposited into
a sediment basin forming flat layers. The
Principle of Superposition states that
sedimentary rock layers on the bottom
formed, or were deposited, first and are
older than layers that formed on the top.
Those small pieces are then glued together
due to compaction and cementation to form
a new rock (kind of like cement). Common
examples include, but are not limited to:
Sandstone, Limestone and
Shale. Sedimentary rocks are the ONLY rocks
that can contain fossils. Limestone is
sedimentary rock that contains Calcite
(calcium carbonate) that comes from
respiration or the shells of organisms living in
the sea. Geologists use an acid solution to
test for Calcite because it fizzes when it
comes in contact with acid.
Weathering
Weathering and Erosion is the process of
weathering and erosion is what continually
changes the face of the Earth. All rocks and
surfaces on the Earth are affected by the
combination of weathering and erosion
Weathering: All weathering deals with the
breaking up of rocks and minerals into
smaller pieces. There are two types of
weathering: Physical (Mechanical), and
Chemical
Physical (Mechanical) Weathering is the type
of weathering that occurs when a rock is
physically broken up due to physical forces.
Examples of physical weathering include:
Abrasion rocks rub or hit against each other
due to the force of gravity and break down
Frost wedging water in the cracks of a rock
freezes and then expands, pushing the rock
apart.
Root wedging the type of weathering that
Principle of Superposition
Abrasion
occurs when a rock is physically broken apart
by the actions of living things (usually plants
and their roots).
Chemical Weathering the type of
weathering that occurs when a rock is broken
down by a chemical reaction. Most common
form of Chemical Weathering is in the form
of acid rain that literally eats away at rocks
Erosion
Erosion is the process that sorts loose
and weathered rock by size, and carries it to
a new site. The smaller the rock size, the
farther the rock will travel. Water, wind, and
glacial ice combined with the force of gravity
can cause erosion. The youngest (top) layers
of sediments usually get eroded first. The
driving force behind erosion
is GRAVITY! There are several types of
erosion:
Water: water running (due to gravity) takes
weathered rock and deposits it elsewhere.
Wind: wind picks up fine sediment and
deposits it elsewhere. Gravity keeps large
sediments from moving, but small particles
(sand, silt and clay) can be blown around by
the wind.
Glaciers (Glaciation): process by which giant
slabs of ice form and grow and recede.
During this process, the ice rips and tears the
land beneath it apart. As the glacier melts, it
deposits the eroded sediment forming
different landforms
Chemical Weathering
Rock Classification Sizes
Fossils
Fossil any remains, trace, or imprint of
animal or plant life preserved in Earth’s crust
Index fossil a fossil that characterizes a
particular period of time. To be considered
an index fossil, must have been distributed
over a wide geographical area, and have lived
for only a short period of time. Index fossils
are useful for indicating the ages of the rock
layers.
Geologic Time
Geologic time is the measurement of time
from the formation of Earth to the present.
The Earth is estimated to be 4.6 billion years
old. Geologic time is broken down into 4
Eras: Cenozoic, Mesozoic, Paleozoic and
Precambrian. Eras are broken down into
Periods. Periods are based on major
evolutionary events that can be determined
by fossil records. Periods are further broken
down into Epochs.
Uniformitarianism a theory that says
geological processes observed in the past are
the same as those observed today, and will
continue to happen in the future
Igneous Rocks
Igneous rocks: Class of rocks that are formed
when magma or lava cools and
solidifies. Igneous literally means fire hence
the name Igneous Rock: rocks that hardened
from molten (on fire) rocks. Any of the other
two types of rock can potentially become an
igneous rock if they are melted back into
magma (liquid rock) and harden
again. Common examples of Igneous rocks
include, but are not limited to: Granite,
Basalt and Obsidian. The presence of crystals
usually indicates an igneous rock. The size of
the crystals indicate the rate at which the
magma or lava cooled. If the magma cooled
slowly underground (intrusive) the crystals
tend to be larger and more visible. If the lava
cooled quickly at or near the surface of the
Earth (extrusive), then the crystals tend to be
smaller and harder to see.
Earthquakes and Volcanoes
Volcanoes result from the subduction of
more dense oceanic plates under less dense
continental plates. Volcanoes occur when
water from the ocean is pulled under the less
dense continental plate and creates pressure
in the magma in the mantle under the
continental crust. This pressure builds up
forcing the magma towards the surface,
eventually causing an eruption.
Earthquakes result from the shifting of the
Earth’s plates and the buildup of tension in
the crust that gets released
Volcanoes and Earthquakes often occur near
tectonic plate boundaries.
Continental Drift
Continental drift - Theory originally
proposed by German Meteorologist Alfred
Wegener, that proposed that the Earth’s
continents are not fixed in one position on
the Earth, rather they are moving around the
surface of the Earth.
Evidence of Continental Drift: There are
many forms of evidence that back up this
theory
1. The coast lines of the Continents
(especially Africa and South America) line up
like pieces of a puzzle. Those pieces can be
put together to form one giant
supercontinent - we believe this
supercontinent, Pangea, existed 250 million
years ago.
2. Rock Samples and fossils taken from the
coasts of South America and Africa match up
perfectly, suggesting the two continents
were once together
3. Fossil records in Antarctica show evidence
of tropical plants. The only way this is
possible is if Antarctica was in a different
location at one point in history.
4. Coal found in cooler climate areas now
formed from when those areas were at one
point located at the equator and were
tropical, and glacial scars found in dry desert
areas of Africa
Theory of Plate Tectonics
Data obtained from seismic wave
studies from large scale earthquakes has
given scientists a virtual picture of what the
inside of the Earth looks like. We know the
Earth consists of 3 main layers:
Crust The outer solid and thinnest layer of
the Earth, and is made of continental crust
which is about 60 miles thick, and oceanic
crust only 10 miles thick at its thinnest. The
crusts and the upper mantle make up the
lithosphere, which houses the tectonic
plates.
Mantle The layer of the Earth below the
crust. The mantle extends below the crust
for about 1,800 miles. Temperatures range
from about 1000 OC to 3000 OC. The
temperature difference in the mantle
causes convection currents in the semi-liquid
material are responsible for moving the
tectonic plates.
Core The Outer Core is the layer of the
Earth below the mantle. Consists of
mostly liquid Iron at a temperature between
4000 OC to 5500 OC. Heat from the outer
core heats up the Earth’s mantle causing the
convection currents that drive plate
tectonics. Inner Core The innermost layer of
the Earth. Consists almost entirely of Solid
Iron and some nickel at a temperature
roughly equivalent to the surface of the sun
(6000 OC). Intense pressure from the
surrounding layers keeps this layer solid.
Tectonic Plate Boundaries
The movements of the plates result in the
creation of earthquakes, volcanoes,
mountain ranges on land and ridges and
trenches in the oceans. There are three main
types of plate boundaries:
Divergent Boundary where two plates move
apart from each other. Divergent boundaries
most often result in the formation of midocean ridges and are responsible for sea floor
spreading. The newest sea floor will be at
the trench in the middle, and the older sea
floor near the continents (Image A)
Convergent Boundary place where two
plates come together. If two continental
plates collide it will result in mountain
ranges. If a less dense continental plate
collides with a more dense oceanic plate, the
ocean plate will go under the continental
plate in a process called subduction.
Subduction leads to the formation
of Volcanoes and can cause Earthquakes
(Image B)
Transform Boundary is a place Where two
plates neither collide nor move apart, instead
they literally slide past each other.
Transform boundaries often result in
earthquakes (Image C)
Mountains
Mountains form over millions of years from
forces that have pushed up or uplifted the
rocks they are made of. Plate movement
provides the force needed to create a
mountain.
Metamorphic Rocks
Metamorphic rocks: Class of rocks that are
formed when either an Igneous rock or
Sedimentary rock undergo INTENSE heat and
pressure, BUT DO NOT MELT. The effect of
heat and pressure warps the rocks causing
changes in their crystals, shape and
coloration. Metamorphosis means a great
change, hence the name Metamorphic rock:
a sedimentary or igneous rock that has
undergone great change. Common examples
of Metamorphic rocks include, but are not
limited to: Slate, Marble, and schist.
Divergent
Boundary
Convergent
Boundary
Transform Boundary
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Earth History Benchmark Study Guide 2014 Sedimentary Rocks