Download Unit C – The Changing Earth(pages 292 – 401)

Science 20 – Unit C Notes-Chapter1_keyed
Mrs. Steinbrenner
Unit C – The Changing Earth (pages 292 – 401)
Unit Overview: The history of our planet is one of change.
There is evidence not only that Earth’s surface is changing but that this change has, in turn, dramatically
impacted the climate and life forms on Earth over time. In this unit, students examine scientific
evidence for natural causes of climate change, for changing life forms and for continual changes to the
Earth’s surface.
Chapter 1 – The Abyss of Time
o Structure of the Earth
o Plate tectonics
o Rock cycle and the fossil record
o Carbon dating
Chapter 2 – A Tropical Alberta
o Fossilization
o Formation of fossil fuels
o Earthquakes and plate tectonics
o Mass extinctions
Chapter 3 – Changing Climates
o Rise of the mammals
o Ice Age
o Earth’s fluctuating climate
Chapter 1 – The Abyss of Time (pages 294 – 327)
1.1 – The Long Beginning (pages 296-301)
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The Earth is constructed of layers:
– arranged according to density
– densest material sinks to core
– lightest material floats at surface
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The density of the Earth increases as you move towards the core.
The core is made of iron and nickel
Layers of the Earth:
– crust/ lithosphere
– asthenosphere
– mesosphere
– liquid outer core
– solid inner core
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Science 20 – Unit C Notes-Chapter1_keyed
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Crust/ Lithosphere:
– includes solid oceanic crust and continental crust that floats on the
asthenosphere
– outermost rigid layer of rock
– 125 km thick
Mantle:
– 80% of Earth’s volume
– solid layer
– 2550 km thick
Mesosphere:
– rigid in behavior
– Lower layer of mantle
Asthenosphere:
– upper layer of mantle; 175km thick
– “plastic” in behavior; can flow up
through crust
Outer core:
– liquid
– made of iron and nickel
– 2260 km thick
Inner core:
– solid
– made of iron and nickel
– radius of 1220 km
What to do: use the information from your notes and the text to fill-in the missing information
Earth’s Layers
Atmosphere
Density
least
dense
Description
Thickness
- gaseous
300 km
- solid
- most rigid layer
mantle
- least rigid or most plastic layer of mantle
- more rigid than uppermost mantle layer
core
outer
core
inner
core
most
dense
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Science 20 – Unit C Notes-Chapter1_keyed
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Deepest wells only scratch Earth’s surface
Earthquakes help in developing theories of Earth’s structure
Theorized that nuclear decay at core provides heat energy that drives flow of matter in
mantle
Hot materials become less dense and rise away from the core, cooling materials become
more dense and sink back down
Process of convection causes the crust to crack, tear and move
Crust exists as “crustal plates” floating on asthenosphere
Plates move a few centimeters per year
Movement has resulted in oceans and mountains
Plate Tectonics
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Plate tectonics is the theory that the lithosphere consists
of crustal plates that slowly move across the mantle and
interact at their boundaries.
Movement of crustal plates is due to convection currents in the mantle.
The Earth has 15 major crustal plates
Sea floor spreading is due to plates separating at mid-ocean ridges.
Youngest rock at spreading center, older rock as they move away
Plate tectonics is confirmed by deep-sea drilling core samples
magnetic properties of ancient rock shows magnetic fields in rock point in opposite
directions
Earth’s magnetic poles have reversed many times in Earth’s history
When two oceanic crustal plates are moving apart the end opposite of spreading is
pushed under neighbouring continental plate.
Oceanic plate melts as it is forced down into the mantle.
Question. Why is the oceanic crust pushed under the continental crust and not vice versa?
The oceanic crust is denser than the continental crust.
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When two crustal plates have equal densities, one plate can’t slide under the other.
Both plates weld together, pushing up huge rock wrinkles to form mountain ranges.
At the site of the weld granite is formed.
Granite outcrops remain long after mountains have eroded away
Outcrop: a part of a rock formation that appears above the surface of the surrounding
land
1.1 Summary
• The Earth has settles into distinct layers dependant on density: core, mantle, crust
• Nuclear reactions in core drive convection currents that push and pull the plates that
make up the crust
Section Questions:
1. Sketch a simple, labeled diagram showing a cross section of Earth.
2. Infer the main property that determines both the ordering and composition of layers
within the Earth.
Density is the main property that determines the composition of layers within Earth.
During Earth’s formation, elements like iron and nickel flowed to the centre of Earth
due to their higher density. Lighter elements—including carbon, silicon, oxygen,
sulfur, nitrogen, and hydrogen—migrated to the crust and atmosphere.
3. Like its name suggests, a lava lamp is a good model of Earth’s convection currents. The
semi-liquid material inside the lamp could represent the mantle. The heat source at the
lamp’s base could represent heat from the Earth’s core.
A bubble starts at the bottom of the lamp, slowly rises, and then s inks again. Explain,
step by step, the forces that affect the movement of fluid bubbles in the lava lamp.
A bubble near the base of the lava lamp is heated. It becomes less dense, so it
floats to the top. Near the top it cools and becomes denser. Once it becomes dense
enough, it sinks to the bottom where it is heated again to complete the cycle.
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1.2 – Early Life (pages 302-305)
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Sedimentary rock is formed from compressed layers of pre-existing rock or organic matter
Properties of sediments and fossils preserved in each strata (layered band) provide
evidence of past environments
Sediments of Cameron Falls were deposited approx 1.5 billion years ago
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A fossil is the evidence or remains of ancient life preserved in Earth’s crust
Oldest evidence of life dates back to 3.8 billion years
Cyanobacteria are oldest known life
• Microscopic photosynthetic single-celled bacteria
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Early Earth was very hostile:
• Frequent volcanic eruptions
• Poisonous gases (methane, hydrogen sulfide)
• Oceans were above 100°C
• Very little oxygen gas
Archaea thrived in these conditions
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1.5 billion years ago, Alberta was a tropical coastal area
Presence of stromatolites in Alberta indicates that cyanobacteria lived in shallow waters
along the coast of ancient Alberta
Stromatolites are layered structures built by cyanobacteria
Growing and dying cyanobacteria slowly deposited layer upon layer of calcium carbonate
(limestone), leaving large mounds
Fossilized stromatolites are called “trace fossils” because they are the remains of the
cyanobacteria and not the organism itself
Stromatolites are Alberta’s oldest fossils
Earth’s Early Atmosphere
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Cyanobacteria use chlorophyll to make glucose from the Sun’s energy, water and carbon
dioxide
Oxygen is a by-product of photosynthesis
Cyanobacteria played a key role in changing the Earth’s atmosphere
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The creation of an oxygen-rich atmosphere is one of the most significant events in
geological time
Impact on the evolution of future life
Impact on Earth’s geology
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Oxygen readily reacts with metals to form compounds
Banded iron; alternating bands of red and grey
Red is iron (III) oxide; Fe2O3(s)
Grey is silica and other minerals
Dissolved iron ions carried to ocean react with free oxygen
If oxygen is present, iron (III) oxide is formed
3O2(g) + 4Fe(aq) 2Fe2O3(s)
Iron (III) oxide is insoluble and sinks to the bottom of the ocean
Iron (III) oxide acts as a chemical indicator of oxygen in Earth’s early atmosphere
Snowball Earth
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Late in the Precambrian Era, life barely survived:
10 million year ice age; termed “snowball Earth”
Small pockets of liquid by thermal vents
Freeze and thaw at the end of ice age may have lead to
Cambrian explosion – huge increase in biodiversity and
complexity of life
1.2 Summary
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The first producers, cyanobacteria, transformed the Earth’s atmosphere
Cyanobacteria left behind stromatolites, Alberta’s oldest fossils
Banded iron shows an increase in free oxygen
The stage was set for dramatic biodiversity following snowball Earth
Section Questions:
1. Identify the process that uses the Sun’s energy to make glucose from carbon dioxide and
water. What is the by-product of this process?
Photosynthesis is the process used to convert carbon dioxide and water into glucose. The byproduct of this process is oxygen.
2. Identify the likely source of oxygen required to form the iron (III) oxide in red layers of
banded iron formations.
The source of oxygen likely came from cyanobacteria. The cyanobacteria produced oxygen
through the process of photosynthesis.
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3. The oldest banded iron formations are 3.8 billion years old. Rock layers below these do not
contain iron (III) oxide.
a) Infer what this suggests about the oxygen level in Earth’s atmosphere before the banded
iron was deposited.
This indicates that significant levels of oxygen were not present in the atmosphere prior to 3.8
billion years ago.
b) Banded iron formations of less than 1.8 billion years ago are extremely rare. Sedimentary
rock layers deposited on top are all rich in iron (III) oxide, but there is no evidence of the
striped iron bands. Conclude what this evidence suggests about atmospheric oxygen
after the banded iron was deposited.
Starting from 1.8 billion years ago, significant levels of oxygen were consistently present.
c) Describe the atmospheric oxygen levels during the time of banded iron formations.
During the time of banded iron formations from 1.8 billion years ago to 3.8 billion years ago,
significant levels of oxygen were present only at certain times (the red bands). At other times,
oxygen was unavailable (the grey bands).
4. Summarize the evidence that present-day Alberta was a hot, tropical, coastal area 1.5
billion years ago.
Stromatolite fossils are found near Alberta’s ancient coastlines. By studying their living
counterparts in Western Australia, scientists know that the Alberta fossils must have required a
hot, tropical, coastal environment.
5. Describe Earth’s first living creatures. How old are the earliest signs of life?
During the time of banded iron formations from 1.8 billion years ago to 3.8 billion years ago,
significant levels of oxygen were present only at certain times (the red bands). At other times,
oxygen was unavailable (the grey bands). The earliest signs of life on Earth are 3.8 billion years
old.
6. Describe the environment in which Earth’s first creatures lived.
Earth’s first creatures lived in hot oceans with temperatures exceeding 100°C.
7. Describe Alberta’s oldest fossils. What did they look like? How were they built?
Alberta’s oldest fossils are stromatolites, which are mounds of limestone over 30 cm in
diameter and up to1 m in height. They were built by cyanobacteria—some of Earth’s first
photosynthetic organisms. Masses of bacteria grew and died, building up layer upon layer of
limestone deposits.
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1.3 – Strange Rocks (pages 306-313)
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Law of superposition: higher strata in a sequence
of rock layers are younger than lower strata
The law of superposition:
Proposed by Nicolas Steno
Gives geologists a way to keep track of order in
which rock layer forms (relative dating)
Relative dating in the process of placing rocks and
geological structures in the correct chronological
order
Pattern of rocks in a strata is called the stratigraphic sequence
Intrusion: A body of a rock that forms from the
invasion of magma into a preexisting rock formation
Intrusion is younger than surrounding rock since it
was formed by molten rock forcing its way through
pre-existing rock
Exception to the law of superposition
The Formation of Sedimentary Rock
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Limitation of relative dating is that it does not reveal the absolute age of events or fossils
Absolute age: the number of years that have elapsed since an event occurred
Question: Determine the relative age of the lava and the road.
The lava must be younger than the road because the
lava is sitting on top of the road.
Question: Explain why you cannot precisely determine
the absolute age of the road or the lava on the road
Absolute dates cannot be determined with the
information given. Only the relative age can be
determined.
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Law of superposition was used by early geologists to rank strata and the fossils
contained in them in chronological order
100 years after Steno, William Smith observed reoccurring fossils at multiple survey sites
Smith argued that the rocks containing the same fossils must correspond closely in age
These distinct fossils are like an index
Index fossil: a fossil used to determine the relative age of a layer in a stratigraphic
sequence or to match stratigraphic sequences from different locations
Index fossils allowed Smith to publish the first geographical map of England
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Science 20 – Unit C Notes-Chapter1_keyed
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What makes an index fossil useful?
• Appears only briefly in geological time
• Has a wide geographical distribution
• Easy to recognize
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During 19th century (1800s) geologists used index fossils to assemble a generalized relative
time scale for all of Earth
Called the Geological Time Scale
First time for a unified history of the Earth
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Geological Time Scale:
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Divided into 4 major eras
– Precambrian
– Paleozoic
– Mesozoic
– Cenozoic
Major eras are broken down into periods
Some periods are broken into epochs
Era  Period  Epoch
1.3 Summary
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Fossils are the remains of once living things
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Law of superposition – rock layer is younger than
those below it
Discovery of index fossils lead to the Geological
Time Scale
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 Eras  Periods  Epochs
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Section Questions
1. Summarize the contribution of Nicolas Steno and William Smith to the field of geology.
Nicolas Steno was one of the first people to recognize that fossils are the remains of once-living
organisms. He also proposed the now fundamental law of superposition, which states that
younger layers are on top of older layers in a stratigraphic sequence. William Smith realized
there is a predictable sequence of rock layers even in very different locations. He invented the
idea of using index fossils to cross-reference rock strata. This idea led to the Geological Time
Scale still used today. Smith also published the first complete geological map of England.
2. Identify the useful qualities of an index fossil.
A useful index fossil only appears for a brief time in the fossil record, is common, and has a wide
geographical distribution. As shown in “Matching Rock Strata from Different Locations,” certain
types of ammonite, graptolite, and placoderm fit this description.
3. List the 4 eras of the Geological Time Scale
The four eras—starting from the oldest—are the Precambrian, Paleozoic, Mesozoic, and
Cenozoic.
4. Describe the criteria geologists use to divide the Geological Time Scale into eras.
The boundaries between eras are marked by noticeable changes in fossils present in the
geological record.
5. Identify which era is more recent – The Triassic of the Permian.
The Triassic Period is more recent.
6. Which epoch are you living in?
Students are living in the Holocene Epoch.
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Science 20 – Unit C Notes-Chapter1_keyed
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1.4 – Getting a Handle on Time (pages 314 – 318)
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Catastrophism is a theory that cites major violent disasters as the main forces that
shape Earth
Believed that these processes were of different type or intensity than observed today
Fit into the understanding of the day
Common belief was that the Earth was several thousand years old
Belief that “present” day changes would have been too gradual to result in the many
geological formations
James Hutton considered “father of modern geology”
Formulated the theory of uniformitarianism
Uniformitarianism: the principle that the geological processes in action today have
always fundamentally operated in the same way throughout Earth’s history
Hutton noticed vertical columns beneath horizontal strata
Layers of unconformity where there was no apparent pattern
Hypothesized vertical columns used to be horizontal but were tilted and followed by
periods of erosions and finally more sediments
The Rock Cycle
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Hutton suggests that the Earth operates on a self-sustaining system driven by
subterranean fire
• Hutton’s thinking started the modern understanding of how rocks form
Types of rock:
– Sedimentary
– Igneous
– Metamorphic
Sedimentary – consists of eroded fragments of other rock types
– Layers of sediments are compressed
– Formed at the surface of the Earth under low temperatures
– Examples: sandstone, banded iron
Igneous rock: forms when molten magma intrudes into the crust or extrudes onto the
surface
– Formed deep in the crust or mantle under extreme heat
– Entire mantle consists of igneous rock
– Examples: granite, basalt
Metamorphic rock: forms when sedimentary or igneous rock is transformed at molecular
level by intense heat and pressure
– Formed at the sites of collision between crustal plates
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– Examples: slate, marble, quartzite
The rock cycle: the continual change of rocks from one type to another.
Driven by energy at Earth’s core.
Charles Lyell used the scientific process to support and strengthen Hutton’s theory of
uniformitarianism
Argued the processes responsible for present day formations have always operated in same
manner
Helped build Geological Time Scale
Great influence on Charles Darwin
1.4 Summary
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Studying Earth’s history is difficult because it occurs on such a large scale
Billions of years recorded in thousand of layers
Given enough time processes have changed Earth many times
Section questions
1. Define catastrophism.
Catastrophism is the theory that violent catastrophes were the prime cause of geological
features. These catastrophes operated in a manner and/or intensity different than the present
processes.
2. Define uniformitarianism.
Uniformitarianism is the principle that all geologic features can be explained in terms of
observable processes still in operation
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3. What are the three main rock types? How does each rock type form?
Igneous rocks form when magma or lava cools and solidifies. Sedimentary rocks form when
wind, water, or ice erodes bits of other rocks and deposits them in layers. Metamorphic rocks
are formed by intense heat and pressure that doesn’t melt the rock but, instead, alters its
molecular structure
4. Sketch a diagram of the rock cycle. Include information on where each type of rock is found
and what processes are responsible for its formation.
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Science 20 – Unit C Notes-Chapter1_keyed
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1.5 – Pinpointing Time (pages 319 – 324)
• Geologists in the late 19 th century generally agreed that the Earth was millions
of years old, but there were no accurate methods to measure the absolute age
of Earth
• Marie Curie discovers radioactivity during the early
20th century
• Discovery of radioactivity leads to a new and accurate
method for measuring the absolute age of rocks.
• Radioactivity: the emission of energy from the nuclei
of unstable atoms as they change to become more stable atoms
• Ernest Rutherford discovered that the energy emitted from radioactive
materials was in the form of high-speed particles.
• Intensity of radiation is measured by detecting the number of particles emitted
per second
• Rutherford discovered the property of radioactive decay
• Every 55.6 s the radioactivity of radon-220 decreased by
half
• The constant time increment for half of a radioactive
sample to decay is called its “half- life”
• Half-life constant is specific to isotope
• Size of radioactive sample does not affect half-life
• Radioactive decay graphs have an exponential curve
• Sketch the curve of a radioactive decay
graph on the blank graph on the left!
• The % of remaining radioactive material
never reaches zero, but gets infinitely close!
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Science 20 – Unit C Notes-Chapter1_keyed
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• Atoms are radioactive because they are unstable
• Radon-220 spontaneously changed into
polonium-216 by losing 2 p+ and 2 no
• Original unstable atom is called parent isotope
• Stable product is called daughter isotope
• The rate of radioactive decay is not affected by
heat, cold or pressure
• All radioactive elements decayed like clockwork – the half-life always elapsed
at constant intervals
• Because radioactive decay of an element occurs at a fixed rate (half-life) the
decay process can be used to measure the time passed since a rock or fossil
formed
• The invention of the mass spectrometer has allows scientists to detect the
elements and their isotopes that are present in a sample of rock
• The percentage of each isotope present in a sample can be determined
To determine the age of a sample:
1) Determine the parent and daughter isotopes by using the table
2) Determine % of each
3) Use decay curve to determine the number of half-lives that have elapsed
4) Look up the amount of time for each half-life for that element. Multiply it
by the number of half-lives that have elapsed
• Tiny crystals called zircons are used to date the rock that they are found in
• Zircons contain uranium and are very durable, making them ideal for
radioactive dating
• The uranium clock is set at zero when the crystal forms and begins to decay
from that point onward
Dating Organic Remains
• Carbon-14 is a rare isotope that is created high in the atmosphere when
nitrogen-14 is bombarded by cosmic radiation
• The carbon-14 is incorporated into plants through the process of
photosynthesis
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• The carbon-14 atoms then make their way into the food chain
• When an animal dies the carbon-14 clock is set at zero because dead
animals don’t ingest carbon.
• If the animals remains are preserved, the date can be determined by
measuring the amount of carbon-14 remaining
1.5 Summary
• The absolute age of rocks and fossils can be determined through
radioactive dating
• The invention of the mass spectrometer has lead to more accurate
predictions of age
• Dates can now be assigned to rock layers that contain radioisotopes
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Section Questions
1. In the fall of 1991, two hikers discovered a human body melting in the glacial
ice of the Italian Alps. It wasn’t until forensic experts were called in that it was
discovered the uniqueness of the find. The frozen body of the hunter was
much older than anyone could have guessed. Carbon-14 dating methods found
that the body contained 52.2% of the original carbon-14 that would have been
in his body at his time of death. Determine the age of the ice mummy.
(0.90 half-lives) (5.73 × 103 a) = 5.2 × 103 a
The age of the hunter is 5.2 × 103 a
2. Carbon-14 dating cannot be used to date samples more than 45 000 years old.
Provide a possible explanation for this.
For carbon-14 dating, 45 000 years is getting near the 8-half-life mark. Carbon-14 is a trace
isotope as it is. At a certain point, it is too hard to detect traces of carbon-14 even when
using a mass spectrometer.
3. Why does radioactivity make a good clock?
The rate of radioactive decay remains the same no matter what. It is impervious to extreme
heat, pressure, and time. Each element has a measurable half-life that ticks by in uniform
increments, like a clock.
4. Describe what radiometric method is used to date organic remains
Carbon-14 dating is used to determine the age of organic remains.
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