Topic 1 introduction

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  • Satellite-based image of Earth. North America can clearly be seen in the center of this view as well as Central America and the northern part of South America. The present locations of continents and ocean basins are the result of plate movements. The interaction of plates through time has affected the physical and biological history of Earth. Source: NASA
  • Figure 1.4 Ferde Grofé’s Grand Canyon Suite pays homage to the grandeur of Arizona’s Grand Canyon.
  • Satellite-based image of Earth. North America can clearly be seen in the center of this view as well as Central America and the northern part of South America. The present locations of continents and ocean basins are the result of plate movements. The interaction of plates through time has affected the physical and biological history of Earth. Source: NASA
  • Solar Nebula Hypothesis Condensation and collapse of interstellar material: a huge nebula condensing under its own gravitational attraction Contracting, Rotating, Flattening of cloud  disk shape Birth of Sun in the center large mass of gaseous, liquid, solid particles (Planetesimals) gathering up, eventually form planets Intense solar radiation blew away unaccreted gas & dust and finally the sun began burning hydrogen, planet completed their formation
  • Figure 1.8 At the stage of development shown here, planetesimals have formed in the inner solar system, and large eddies of gas and dust remain at great distances from the protosun.
  • Figure 1.7 Diagrammatic representation of the solar system, showing the planets and their orbits around the Sun.
  • Figure 1.9 Homogeneous accretion theory for the formation of a differentiated Earth. Early Earth was probably of uniform composition and density throughout. Heating of early Earth reached the melting point of iron and nickel, which, being denser than silicate minerals, settled to Earth’s center. At the same time, the lighter silicates flowed upward to form the mantle and the crust. In this way, a differentiated Earth formed, consisting of a dense iron–nickel core, an iron-rich silicate mantle, and a silicate crust with continents and ocean basins.
  • Satellite-based image of Earth. North America can clearly be seen in the center of this view as well as Central America and the northern part of South America. The present locations of continents and ocean basins are the result of plate movements. The interaction of plates through time has affected the physical and biological history of Earth. Source: NASA
  • Figure 1.10 A cross section of Earth, illustrating the core, mantle, and crust. The enlarged portion shows the relationship between the lithosphere(composed of the continental crust, oceanic crust, and solid upper mantle) and the underlying asthenosphere and lower mantle.
  • Figure 1.10 A cross section of Earth, illustrating the core, mantle, and crust. The enlarged portion shows the relationship between the lithosphere(composed of the continental crust, oceanic crust, and solid upper mantle) and the underlying asthenosphere and lower mantle.
  •   - convection is the process by which hot, less-dense materials rise upward and are replaced by cold, downward/sideways flowing materials - this process operates in the Earth’s interior - very slow convection currents   - convection causes movement and shapes the Earth’s surface - hot rock rises slowly from deep inside the Earth, cools, flows sideways and sinks - controls the positions and movement of ocean basins and continents - hot material that escapes this convection loop is expelled at the surface or in the atmosphere by volcanoes   - most important effect of convection currents inside the Earth is plate tectonics - the slow, lateral movement of segments of the Earth’s hard, outermost shell - movement of the plates that splits and moves continents, forms mountains, trigger earthquakes and causes volcanoes to be located where they are - convection currents, via plate tectonics, continually shape and change the face of the Earth since the widespread acceptance of plate tectonic theory about 25 years ago, geologists have viewed the Earth as a number of interconnected systems - distribution of mountain chains, major fault systems, volcanoes, earthquakes, origin of new ocean basins, movement of continents, break-up of continents and many other geological processes are perceived to be interrelated
  • Figure 1.2 The atmosphere, biosphere, hydrosphere, lithosphere, mantle, and core can all be thought of as subsystems of Earth. The interactions among these subsystems are what make Earth a dynamic planet, which has evolved and changed since its origin 4.6 billion years ago.
  • Figure 1.12 Earth’s lithosphere is divided into rigid plates of various sizes that move over the asthenosphere.
  • Figure 1.12 Earth’s lithosphere is divided into rigid plates of various sizes that move over the asthenosphere.
  • Figure 1.11 Earth’s plates are thought to move as a result of underlying mantle convection cells in which warm material from deep within Earth rises toward the surface, cools, and then, upon losing heat, descends back into the interior. The movement of these convection cells is thought to be the mechanism responsible for the movement of Earth’s plates, as shown in this diagrammatic cross section.
  • To view this animation, click “View” and then “Slide Show” on the top navigation bar.
  • discussed further in the following five sections: - igneous rocks (Topic 3) - volcanism (Topic 4) - weathering and sediments (Topic 5) - sedimentary rocks (Topic 6) - metamorphic rocks (Topic 7)   - see course outline   - terms “rocks” and “minerals” will be defined in Topic 2 - rocks provide a record of plate tectonic events which have happened in the past.     - there are three different types of rocks - igneous: from melted rock material(lava or magma solidifies) - sedimentary: broken up rock material(weathered) or chemical/biochemical precipitation - metamorphic: new rocks formed from old rocks as a result of pressure and tempreture   - each rock group contains a variety of individual rock types that differ from one another on the basis of composition or texture (size, shape and arrangement of mineral grains)   e.g. sandstone, slate, granite
  • Figure 1.15 Hand specimens of common igneous (a, b), sedimentary (c, d), and metamorphic (e, f) rocks. (a) Granite, an intrusive igneous rock. (b) Basalt, an extrusive igneous rock. (c) Conglomerate, a sedimentary rock formed by the consolidation of rock fragments. (d) Limestone, a sedimentary rock formed by the extraction of mineral matter from seawater by organisms or by the inorganic precipitation of the mineral calcite from seawater. (e) Gneiss, a foliated metamorphic rock. (f) Quartzite, a nonaffiliated metamorphic rock.
  • Figure 1.15 Hand specimens of common igneous (a, b), sedimentary (c, d), and metamorphic (e, f) rocks. (a) Granite, an intrusive igneous rock. (b) Basalt, an extrusive igneous rock. (c) Conglomerate, a sedimentary rock formed by the consolidation of rock fragments. (d) Limestone, a sedimentary rock formed by the extraction of mineral matter from seawater by organisms or by the inorganic precipitation of the mineral calcite from seawater. (e) Gneiss, a foliated metamorphic rock. (f) Quartzite, a nonaffiliated metamorphic rock.
  • Figure 1.15 Hand specimens of common igneous (a, b), sedimentary (c, d), and metamorphic (e, f) rocks. (a) Granite, an intrusive igneous rock. (b) Basalt, an extrusive igneous rock. (c) Conglomerate, a sedimentary rock formed by the consolidation of rock fragments. (d) Limestone, a sedimentary rock formed by the extraction of mineral matter from seawater by organisms or by the inorganic precipitation of the mineral calcite from seawater. (e) Gneiss, a foliated metamorphic rock. (f) Quartzite, a nonaffiliated metamorphic rock.
  • Figure 1.15 Hand specimens of common igneous (a, b), sedimentary (c, d), and metamorphic (e, f) rocks. (a) Granite, an intrusive igneous rock. (b) Basalt, an extrusive igneous rock. (c) Conglomerate, a sedimentary rock formed by the consolidation of rock fragments. (d) Limestone, a sedimentary rock formed by the extraction of mineral matter from seawater by organisms or by the inorganic precipitation of the mineral calcite from seawater. (e) Gneiss, a foliated metamorphic rock. (f) Quartzite, a nonaffiliated metamorphic rock.
  • Figure 1.15 Hand specimens of common igneous (a, b), sedimentary (c, d), and metamorphic (e, f) rocks. (a) Granite, an intrusive igneous rock. (b) Basalt, an extrusive igneous rock. (c) Conglomerate, a sedimentary rock formed by the consolidation of rock fragments. (d) Limestone, a sedimentary rock formed by the extraction of mineral matter from seawater by organisms or by the inorganic precipitation of the mineral calcite from seawater. (e) Gneiss, a foliated metamorphic rock. (f) Quartzite, a nonaffiliated metamorphic rock.
  • Figure 1.15 Hand specimens of common igneous (a, b), sedimentary (c, d), and metamorphic (e, f) rocks. (a) Granite, an intrusive igneous rock. (b) Basalt, an extrusive igneous rock. (c) Conglomerate, a sedimentary rock formed by the consolidation of rock fragments. (d) Limestone, a sedimentary rock formed by the extraction of mineral matter from seawater by organisms or by the inorganic precipitation of the mineral calcite from seawater. (e) Gneiss, a foliated metamorphic rock. (f) Quartzite, a nonaffiliated metamorphic rock.
  • Figure 1.14 The rock cycle showing the interrelationships between Earth’s internal and external processes and how the three major rock groups are related. Rock Cycle - relates the 3 rock groups to one another - interrelationships between the Earth’s internal and external processes   - surface processes: weathering, transportation and deposition - internal processes: magma generation and metamorphism   - plate movements drives the rock cycle - recycling rock materials (subduction)   - plate interactions determine to some degree which rock type will form - e.g. igneous and metamorphic rocks are generated along convergent margins due to the melting of previously deposited sedimentary rocks or igneous rocks (oceanic crust) - sedimentary rocks are buckled and thrusted upwards to form mountain chains - eventually these mountains are eroded and the sediments are transported back into the ocean basin to renew the cycle
  • Figure 1.14 The rock cycle showing the interrelationships between Earth’s internal and external processes and how the three major rock groups are related.
  • Figure 1.16 Plate tectonics and the rock cycle. The cross section shows how the three major rock groups—igneous, metamorphic, and sedimentary—are recycled through both the continental and oceanic regions.
  • Figure 1.16 Plate tectonics and the rock cycle. The cross section shows how the three major rock groups—igneous, metamorphic, and sedimentary—are recycled through both the continental and oceanic regions.
  • Figure 1.17The geologic time scale. Numbers to the right of the columns are ages in millions of years before the present.
  • Age of the Earth 4.55 billions years (4 550 000 000 years) ........ First fossils (algae) 545 millions years ago (545 000 000 years) Abundant reptiles 230 millions years ago Dinosaurs extinction 65 millions years ago Earliest hominids 3 millions years
  • Topic 1 introduction

    1. 1. Introduction to Earth Science 42:160 Dr. Simon A.J. Pattison Department of Geology
    2. 2. Topic 1A - Introduction Outline Course Logistics Course Objectives What is Geology? Geology: Practical Applications Being a Geologist Physical vs. Historical Geology
    3. 3. Course Logistics Course Outline/Lab Schedule Instructor: Dr. Simon A.J. Pattison Brodie Bldg 2-7 727-7468 (voice mail available) Policy on Office Hours: Open Door (8:00 am to 5:00 pm, M to F)     Lecture notes available on the s:drive. Students on ‘Weber/Vol15’ (S:) Geology, Pattison, 160 Introduction to Earth Science   - files are read-only - download notes and save as separate file names to your memory stick - switch-out of read-only and reformat/revise/annotate
    4. 4. Excellent textbook Second hand copies should be available. Students are responsible for reading the assigned chapters   Course structure closely follows the textbook structure However, lots of additional material will be presented in class, therefore, please attend   Different textbook used for Historical Geology (42:161) Second term geology course (Slot 5), for those interested Also has a lab component (Wednesday Afternoon)   Two other courses offered in 1 st year geology Our Dynamic Earth (42:162): Slot 5, Term 1, Theater B This Old Earth: A Trip Through Time (42:163): Slot 5, Term 2, Theater B Both of these courses do not have labs Designed mostly for non-science students
    5. 5. Teacher Expectations: Hard Work   Read Textbook   Ask Questions - lots of terminology in geology - I may use terms in the lecture that you have not heard before - please stop me and ask me to define and clarify   Turn Off Cell Phones/No Texting Lap Tops: Lecture Notes Only   No Talking - respect fellow students - hard to listen or concentrate with background talking - if you need to talk, please leave my class (door is unlocked)
    6. 6. Course Objectives (a) Provide an introduction to earth science, especially physical geology. (b) Review and describe Earth materials: minerals and rocks. - strong emphasis in the lab (c) Understand the processes which make our Earth dynamic. - earthquakes, volcanoes, weathering/transport (e.g. rivers, ocean waves) (d) Learn the significance of plate tectonic theory to modern geology. - unifying theory that explains many geological features (e.g. mountains) - theory developed in the 1960’s (e) Emphasize examples and practical applications where appropriate. - geology is very applied and practical
    7. 7. What is Geology?   Geology is defined as the study of the Earth.   Geology: geo- (Greek roots, meaning “of the Earth”) -logia or -logos (Greek roots, meaning study or science)   Scientists who study the Earth are called geologists.   Some questions that geologists could ask: What causes earthquakes? Why do earthquakes occur in some regions and not in others? Similar questions for volcanoes. What processes lead to mountain building? What rate? What controls mountain growth? Why are mountains present on the West Coast of Canada and not in Central Canada? Does sea level rise and fall? What controls sea level change?
    8. 8. Earth is always changing. Small/slow vs. large/rapid changes.   Small slow changes. e.g. mountain building, cm per 100 years. Continuous. Gradualism. e.g. Rocky Mountains (slow upward movement).   vs.   Rapid changes. e.g. hurricane ripping up a beach/coastline. e.g. volcanic eruption. Catastrophic.
    9. 9. Geology is a unique science because the geological laboratory is the world in which we live. Very difficult for geologists to carry out controlled experiments. Problems with space and time.   Geologists must study the Earth as it exists today. From their assembled observations they can draw conclusions about the processes that are shaping the Earth today and events that have shaped the Earth over the past 4.5 billion years. Increasingly geologists are called upon to use their understanding of the Earth machine to make predictions on future change. e.g. global warming.   “ Present is the key to the past ”. Fundamental principle in geology.
    10. 10. Grand Canyon - Arizona
    11. 11. Six key aspects to the science of geology: A. Solid Earth/Earth Materials B. History of Life C. History of the Earth D. Study of Earth Resources E. Earth Hazards (egs. earthquakes, volcanoes, landslides, subsidence, coastal erosion) F. Solid Bodies in the Solar System
    12. 12. Geology: Practical Applications   Geologists work in every corner of the Earth. Government, academia and industry. e.g. hydro-geologist: ground water movement, environmental impact assessment (EIA), pollutants (location, mobility, mitigation). e.g. predict location of new oil fields. e.g. predict best location for a water well. e.g. location of rich ore deposits.    Geology discipline is very broad. Many specialties. Also geologists are interdisciplinary in nature. i.e. work with many other disciplines. Interaction with physics, chemistry, biology and engineering. e.g. petroleum geologist (oil and gas). e.g. paleontologist (fossils). e.g. hydro-geologist- geology, chemistry, 3D modelling(simulation).   “ Earth scientist”: e.g. shark’s tooth discovered in the desert of Utah? How did it get there? How old? What does this imply for environmental change? Rate? Magnitude of change?
    13. 13. BU Geologists: 85 % of our graduates from the 4-year Honours program continue in a geology-related career. Get any geological-related experience possible. Co-op work experience program in conjunction with BU alumni, petroleum and mining industries and appropriate government departments. Students gain project-oriented employment skills. Ensures a steady stream of graduates with both industry and applied research experience. Practical training.   Graduates have travelled and worked in Africa, Middle East, SE Asia, Chile, Holland, Scotland, USA and throughout Canada. Petroleum industry. Mineral exploration and mining industry. Environmental careers (government, industry, academia). Graduate school (M.Sc. and Ph.D.).
    14. 15. Majors in Geology What do they do? Where do they go?   Petroleum Mining Environmental Government Academia/Education   With the appropriate geology degree and additional work experience, one can obtain designation as a professional geoscientist (P. Geo.) in Manitoba.     Minors in Geology What do they do? Where do they go?   Business (resources) Education (teaching) Other Sciences (biology, chemistry, physics, engineering, geography) Environmental
    15. 16. Being a Geologist: <ul><li>Outside! </li></ul>Where do we start?
    16. 17. Field work… Equipment… Transport… Camp…
    17. 18. Tourist field work…
    18. 19. Field work in remote area
    19. 20. Nice things about field work…
    20. 21. Nice things about field work…
    21. 22. Surprises…
    22. 23. Earth Scientists... <ul><li>Exploration Geologist </li></ul><ul><li>Mapping Geologist </li></ul><ul><li>Geological surveys </li></ul><ul><ul><li>Provincial / Territorial </li></ul></ul><ul><ul><li>Federal (GSC) </li></ul></ul><ul><li>Mining Geologist </li></ul><ul><li>Petroleum Geologist </li></ul><ul><li>Hydrogeologist </li></ul><ul><li>Environmental Geologist </li></ul><ul><li>Geological Engineer </li></ul>
    23. 24. Example of an Earth Scientist: Hydrogeologist Environmental Geologist <ul><li>Degree needed: </li></ul><ul><ul><li>B.Sc. , +/- M.Sc., +/- Ph.D. </li></ul></ul><ul><ul><li>Geology, Hydrology, Hydrogeology, Chemistry, Math, Sedimentology, Computer Modelling... </li></ul></ul><ul><li>Type of work: </li></ul><ul><ul><li>9:00 am – 5:00 pm </li></ul></ul><ul><ul><li>Office work / computer / field work... </li></ul></ul><ul><li>Salary (see handout). </li></ul>
    24. 25. Let’s find water...
    25. 26. Let’s pump it... Dug well
    26. 27. Contaminant Propagation
    27. 28. Contaminant monitoring... trench
    28. 29. Remediation and/or Risk Assessment <ul><li>Remediation </li></ul><ul><ul><li>removal </li></ul></ul><ul><li>Risk assesment </li></ul><ul><ul><li>Contaminant </li></ul></ul><ul><ul><li>Pathway </li></ul></ul><ul><ul><li>Receptors </li></ul></ul>
    29. 30. Physical vs. Historical Geology Geology has traditionally been divided into two broad topic areas: physical geology, and historical geology.   physical geology – concerned with understanding the processes that operate at or beneath the surface of the Earth and the materials on which these processes operate.   Physical geology is the main focus of this course (42:160). Also the main focus of Our Dynamic Earth (42:162): Slot 5, no labs!   Questions to ponder: What causes a volcano to erupt? How can we predict earthquake activity? How do we minimize the risk of loss of life and property damage from floods and landslides?   Problems in geology: time and scale. Dealing with complexity of natural systems.
    30. 31. historical geology – concerned with the chronology of physical and biological events that occurred in the past.   Recommend the following course for those of you that are interested: Historical Geology (42:161): Slot 5, Wed labs, next term. This Old Earth: A Trip Through Time (42:163): Slot 5, no labs, next term.   Questions to ponder: When were the oceans formed? When did oxygen first occur in the atmosphere? How did plants evolve? Why did dinosaurs become extinct? What was the Earth’s climate in the geological past: Hotter? Colder?   Very practical reason for studying the Earth. Understand the environment in which we live and make predictions about changes that might occur in the future. In order to fully understand how we humans may be affecting the Earth, we need to examine both the Earth’s materials and processes.
    31. 32. Topic 1B - Introduction Outline Origin: Universe and Solar System Earth a Dynamic Planet Convection Plate Tectonics Plate Boundaries Rock Types Rock Cycle Plate Tectonics and Rock Cycle Geologic Time Principle of Uniformitarianism
    32. 33. Origin of the Universe and Solar System <ul><li>Universe formation </li></ul><ul><li>(BIG BANG) </li></ul><ul><ul><li>13.7 billion years ago </li></ul></ul><ul><li>Solar system formation </li></ul><ul><ul><li>4.6 billion years ago </li></ul></ul>Nebula Rotation Contraction Sun (fusion - core) Planets (dust...)
    33. 35. Our solar system…
    34. 36. Earth formation… 4.6 billion years ago
    35. 38. Earth a Dynamic Planet <ul><li>The Core </li></ul><ul><ul><li>Solid inner. Liquid outer. Density of 9-13 g/cm³. </li></ul></ul><ul><li>The Mantle </li></ul><ul><ul><li>Surrounds the core. Density of 3.3-5.7g/cm³. Three distinct zones. </li></ul></ul><ul><li>The Crust </li></ul><ul><ul><li>Oceanic - 3 g/cm³. Continental - 2.7 g/cm³. </li></ul></ul><ul><li>Plate Tectonic Theory explains the interactions of these zones. Earth’s internal heat causes volcanoes and earthquakes, and mountains to rise and continents to move. </li></ul><ul><li>Geothermal gradient : Rate of temperature increase with depth. Varies from 15-75 ° C/km. Average: 25 ° C/km. </li></ul>
    36. 40. Convection Process by which hot, less-dense materials rise upward and are replaced by cold, downward and sideways flowing material. Operates in the Earth’s interior. Moves tectonic plates.
    37. 42. Plate Tectonics Has provided a framework for interpreting the composition, structure and internal processes of the Earth on a global scale.
    38. 43. Plate tectonic theory is a unifying theory that explains the following earth patterns: A. Occurrence and distribution of earthquakes and volcanoes (i.e. mostly in linear zones). B. Volcanoes and earthquakes occur together. C. Large earthquakes occur in zones where there are long narrow deep sea trenches. D. Why the ocean contains deep trenches and high ridges. E. Jigsaw fit of the continents. F. Why mountain building occurs. G. Distribution of ore and petroleum deposits.
    39. 45. Theory of plate tectonics: Outer surface of the Earth is relatively cool and rigid: LITHOSPHERE. Middle part of Earth is hotter and somewhat viscous: ASTHESNOSPHERE. Lithosphere floats on the asthenosphere: ISOSTASY. The lithosphere is divided up into a number of PLATES. CONVECTION occurs in the asthenosphere, and this is one of the main reasons the plates move. Deformation, volcanoes, and earthquakes mostly occur at the edges of the plates, not in their interiors. Therefore most of the geological action occurs at the PLATE BOUNDARIES. Plate Tectonics is a global model for the Earth as a DYNAMIC SYSTEM.
    40. 47. Convection and Tectonics
    41. 48. Plate Boundaries: <ul><li>3 types: </li></ul><ul><ul><li>Divergent </li></ul></ul><ul><ul><li>Convergent </li></ul></ul><ul><ul><li>Transform </li></ul></ul>
    42. 49. Divergent Plate Boundary <ul><li>Plates move apart. </li></ul><ul><li>Magma rises to the surface. </li></ul><ul><li>New oceanic crust is generated. </li></ul>
    43. 50. Convergent Plate Boundary <ul><li>Plates move together and collide. </li></ul><ul><li>One plate sinks beneath the other plate… subduction zone. </li></ul><ul><li>Associated with major mountain belts. </li></ul>
    44. 51. Transform Plate Boundary <ul><li>Plates slide sideways past one another. </li></ul><ul><li>e.g. San Andreas fault in California. </li></ul>
    45. 52. Rock Types There are THREE different types of rocks: Igneous Metamorphic Sedimentary Each group contains a variety of individual rock types that differ from one another on the basis of composition (mineralogy/chemistry) or texture (size, shape and arrangement of mineral grains)
    46. 53. Igneous Rock Granite
    47. 54. Igneous Rock Basalt
    48. 55. Sedimentary Rock Conglomerate
    49. 56. Sedimentary Rock Limestone
    50. 57. Metamorphic Rock Gneiss
    51. 58. Metamorphic Rock Quartzite
    52. 59. Rock Cycle Relates the 3 rock groups to one another. Igneous: from melted rock material (lava or magma solidifies). Sedimentary: broken up rock material (weathered) or chemical/biochemical precipitation (evaporites – salts, carbonate particles – reefs). Metamorphic: new rocks formed from old rocks as a result of pressure and temperature (no melting).   Interrelationships between the Earth’s internal and external processes. Surface processes: weathering, transportation and deposition. Internal processes: magma generation and metamorphism.
    53. 61. Plate Tectonics and the Rock Cycle Plate movements drives the rock cycle. Recycling rock materials (subduction).   Plate interactions determine to some degree which rock type will form. e.g. igneous and metamorphic rocks are generated along convergent margins due to the melting of previously deposited sedimentary rocks or igneous rocks (oceanic crust). Sedimentary rocks are buckled and thrusted upwards to form mountain chains. Eventually these mountains are eroded and the sediments are transported back into the ocean basin to renew the cycle.
    54. 63. Geologic Time Not in years, months, days, minutes, seconds… But in hundreds of thousands, millions, and billions years!
    55. 64. <ul><li>First fossils (algae) </li></ul><ul><ul><li>3.5 billion years ago </li></ul></ul><ul><ul><li>First fossils (animals-invertebrates) </li></ul></ul><ul><ul><li>- 545 million years ago </li></ul></ul>Geologic Time <ul><li>Age of the Earth </li></ul><ul><ul><li>4.55 billion years ago (4,550,000,000 yrs) </li></ul></ul><ul><li>Dinosaurs extinction </li></ul><ul><ul><li>65 million years ago </li></ul></ul><ul><li>Abundant reptiles </li></ul><ul><ul><li>230 million years ago </li></ul></ul><ul><li>Earliest hominids </li></ul><ul><ul><li>3 million years ago </li></ul></ul>Earth algae
    56. 65. Principle of Uniformitarianism <ul><li>Laws of nature have been constant through time. </li></ul><ul><li>Present day processes have operated throughout Earth’s history. </li></ul><ul><li>Therefore we can better understand past events by studying modern processes. </li></ul><ul><li>“ The present is the key to the past .” </li></ul>

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