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Unit C – The Changing Earth

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1 Unit C – The Changing Earth
Pages

2 The history of our planet is one of change
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.

3 Unit Overview Chapter 1 – The Abyss of Time Structure of the Earth
Plate tectonics Rock cycle and the fossil record Carbon dating

4 Unit Overview Chapter 2 – A Tropical Alberta Fossilization
Formation of fossil fuels Earthquakes and plate tectonics Mass extinctions

5 Unit Overview Chapter 3 – Changing Climates Rise of the mammals
Ice Age Earth’s fluctuating climate

6 Chapter 1 – The Abyss of Time (pages 294 – 327)

7 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

8 The density of the Earth increases as you move towards the core.
The core is made of iron and nickel

9 Layers of the Earth: crust/ lithosphere asthenosphere mesosphere liquid outer core solid inner core

10 Layers of the Earth

11 Crust/ Lithosphere: includes solid oceanic crust and continental crust that floats on the asthenosphere outermost rigid layer of rock 125 km thick

12 solid layer 2550 km thick rigid in behavior Lower layer of mantle
80% of Earth’s volume solid layer 2550 km thick Mesosphere: rigid in behavior Lower layer of mantle

13 Asthenosphere: upper layer of mantle; 175km thick
“plastic” in behavior; can flow up through crust

14 made of iron and nickel Inner core: Outer core: liquid 2260 km thick
solid radius of 1220 km

15 Earth’s Layers Density Description Thickness Atmosphere least dense
most dense - gaseous 300 km solid most rigid layer mantle - least rigid or most plastic layer of mantle - more rigid than uppermost mantle layer core outer inner

16 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

17 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

18 Crust exists as “crustal plates” floating on asthenosphere
Plates move a few centimeters per year Movement has resulted in oceans and mountains

19 Plate Tectonics 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.

20 The Earth has 15 major crustal plates

21 Convection in the Mantle Animation

22 Sea floor spreading is due to plates separating at mid-ocean ridges.
Youngest rock at spreading center, older rock as they move away

23 Plate tectonics is confirmed by deep-sea drilling core samples

24 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

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26 Oceanic plate melts as it is forced down into the mantle.
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. Why is the oceanic crust pushed under the continental crust and not vice versa?

27 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

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29 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

30 1.2 – Early Life (pages )

31 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

32 Oldest evidence of life dates back to 3.8 billion years
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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34 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

35 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

36 Stromatolites are layered structures built by cyanobacteria
Growing and dying cyanobacteria slowly deposited layer upon layer of calcium carbonate (limestone), leaving large mounds

37 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

38 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

39 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

40 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

41 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 Explanation of banded iron formation

42 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 Snowball Earth Clip

43 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

44 Challenge Question (page 305, #8)
Shown is a 700 million-year-old sedimentary rock in Namibia. The big embedded rocks are the type that glaciers pick up and carry with them as they flow. Define the climate theory supported by these glacial deposits. Just above the geologists hands are sedimentary layers of limestone known only to be deposited in warm seas. What do these limestone deposits indicate?

45 1.3 – Strange Rocks (pages 306-313)
Nicolas Steno wondered how fossilized shark teeth could end up embedded in stone high above sea level. What processes might have been involved?

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47 Law of superposition: higher strata in a sequence of rock layers are younger than lower strata

48 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

49 Intrusion: A body of a rock that forms from the invasion of magma into a pre-existing 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

50 The Formation of Sedimentary Rock

51 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. Question: Explain why you cannot precisely determine the absolute age of the road or the lava on the road

52 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

53 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

54 Index fossils allowed Smith to publish the first geographical map of England

55 What makes an index fossil useful?
Appears only briefly in geological time Has a wide geographical distribution Easy to recognize

56 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

57 Divided into 4 major eras Precambrian Paleozoic Mesozoic Cenozoic
Geological Time Scale: 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

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59 1.3 Summary Fossils are the remains of once living things
Law of superposition – rock layer is younger than those below it Discovery of index fossils lead to the Geological Time Scale Eras  Periods  Epochs

60 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

61 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

62 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

63 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

64 The Rock Cycle 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

65 Types of rock: Sedimentary Igneous Metamorphic

66 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

67 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

68 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 Examples: slate, marble, quartzite

69 The rock cycle: the continual change of rocks from one type to another.
Driven by energy at Earth’s core.

70 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

71 1.4 Summary 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

72 1.5 – Pinpointing Time (pages 319 – 324)
Geologists in the late 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

73 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.

74 Radioactivity: the emission of energy from the nuclei of unstable atoms as they change to become more stable atoms

75 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

76 Rutherford discovered the property of radioactive decay
Every 55.6 s the radioactivity of radon-220 decreased by half Time elapsed Radioactivity 0 time 100% 55.6 s 50% 55.6 s (x2) 25% 55.6 s (x3) 12.5%

77 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

78 Radioactive decay graphs have an exponential curve
The % of remaining radioactive material never reaches zero, but gets infinitely close!

79 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

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81 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

82 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

83 To determine the age of a sample:
Determine the parent and daughter isotopes by using the table Determine % of each Use decay curve to determine the number of half-lives that have elapsed Look up the amount of time for each half-life for that element. Multiply it by the number of half-lives that have elapsed

84 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

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87 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 The carbon-14 atoms then make their way into the food chain

88 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

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90 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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95 Ocean seismic technology animation

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