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) •

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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Mrs. Steinbrenner

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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Mrs. Steinbrenner

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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Science 20 – Unit C Notes-Chapter1_keyed

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Mrs. Steinbrenner

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. 4

Science 20 – Unit C Notes-Chapter1_keyed

Mrs. Steinbrenner

1.2 – Early Life (pages 302-305) • • •

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 • • •

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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Science 20 – Unit C Notes-Chapter1_keyed

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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 • • • •

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 • • • •

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. 6

Science 20 – Unit C Notes-Chapter1_keyed

Mrs. Steinbrenner

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. 7

Science 20 – Unit C Notes-Chapter1_keyed

Mrs. Steinbrenner

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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Science 20 – Unit C Notes-Chapter1_keyed

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Mrs. Steinbrenner

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 

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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Science 20 – Unit C Notes-Chapter1_keyed

Mrs. Steinbrenner

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

Mrs. Steinbrenner

1.4 – Getting a Handle on Time (pages 314 – 318) • • • • • • • • • • •

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 12

Science 20 – Unit C Notes-Chapter1_keyed

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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

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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 13

Science 20 – Unit C Notes-Chapter1_keyed

Mrs. Steinbrenner

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

Mrs. Steinbrenner

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

Mrs. Steinbrenner

• 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 16

Science 20 – Unit C Notes-Chapter1_keyed

Mrs. Steinbrenner

• 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 17

Science 20 – Unit C Notes-Chapter1_keyed

Mrs. Steinbrenner

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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