Presentation is loading. Please wait.

Presentation is loading. Please wait.

Geologic Time 1. Which geologic event took place first and when? when? Which rock layer is older, and how is earth Which rock layer is older, and how.

Similar presentations


Presentation on theme: "Geologic Time 1. Which geologic event took place first and when? when? Which rock layer is older, and how is earth Which rock layer is older, and how."— Presentation transcript:

1 Geologic Time 1

2 Which geologic event took place first and when? when? Which rock layer is older, and how is earth Which rock layer is older, and how is earth history deciphered? history deciphered? How do we assign actual years to rock layers? How do we assign actual years to rock layers? Which geologic event took place first and when? when? Which rock layer is older, and how is earth Which rock layer is older, and how is earth history deciphered? history deciphered? How do we assign actual years to rock layers? How do we assign actual years to rock layers? Consider: Sandstone (ss) Limestone (LS) Shale (sh) ss The earth needs a time scale The earth needs a time scale

3 Historical aspects about geology There are two schools of thought on the geologic history and processes that formed our earth. Historical aspects about geology There are two schools of thought on the geologic history and processes that formed our earth. Catastrophism vs. Uniformitarianism 4

4 Catastrophism: (mid-1600s) powerful geologic events that shape the earth in a single incident Volcanic eruptions Earthquakes Massive floods Landsliding Catastrophism: (mid-1600s) powerful geologic events that shape the earth in a single incident Volcanic eruptions Earthquakes Massive floods Landsliding 5

5 Catastrophism: (mid-1600s) published by Anglican Archbishop, James published by Anglican Archbishop, James Ussher Ussher determined that earth was only a few determined that earth was only a few thousand years old – created in 4004 BC thousand years old – created in 4004 BC suggested that earth landscapes are suggested that earth landscapes are fashioned by great catastrophes fashioned by great catastrophes an attempt to fit the formation of earth an attempt to fit the formation of earth features into a short amount of time features into a short amount of time (6000 years – Biblical philosophy) (6000 years – Biblical philosophy) Catastrophism: (mid-1600s) published by Anglican Archbishop, James published by Anglican Archbishop, James Ussher Ussher determined that earth was only a few determined that earth was only a few thousand years old – created in 4004 BC thousand years old – created in 4004 BC suggested that earth landscapes are suggested that earth landscapes are fashioned by great catastrophes fashioned by great catastrophes an attempt to fit the formation of earth an attempt to fit the formation of earth features into a short amount of time features into a short amount of time (6000 years – Biblical philosophy) (6000 years – Biblical philosophy) 6

6 Uniformitarianism – Birth of Modern Geology The present is the key to the past. The present is the key to the past. Uniformitarianism – Birth of Modern Geology The present is the key to the past. The present is the key to the past. Uniformitarianism states: Physical, chemical, and biological laws that operate today have also operated in the geologic past. geologic past. Uniformitarianism states: Physical, chemical, and biological laws that operate today have also operated in the geologic past. geologic past. Proposed by James Hutton – late 1700s argued using the rock cycle concept argued using earth processes that can be observed What is required? TIME Proposed by James Hutton – late 1700s argued using the rock cycle concept argued using earth processes that can be observed What is required? TIME 7

7 The Uniformitarianism philosophy Do geologic processes act slowly or rapidly? How many catastrophic events take place/day? When was the last major volcanic eruption? When was the last major earthquake? How long does it take a river to carve a canyon? How fast are the continents moving? Do you consider yourself a catastrophist or a uniformitarianist? The Uniformitarianism philosophy Do geologic processes act slowly or rapidly? How many catastrophic events take place/day? When was the last major volcanic eruption? When was the last major earthquake? How long does it take a river to carve a canyon? How fast are the continents moving? Do you consider yourself a catastrophist or a uniformitarianist? 8

8 Taking Uniformitarianism literally – Problem with U Rates and intensities of geologic processes change over time. Example: 10,000 years ago, large land masses were covered in ice. Different type of geologic environment than today Different intensity Different rates of erosion Given the concept of Uniformitarianism, would you consider the earth to be very OLD or very YOUNG? Taking Uniformitarianism literally – Problem with U Rates and intensities of geologic processes change over time. Example: 10,000 years ago, large land masses were covered in ice. Different type of geologic environment than today Different intensity Different rates of erosion Given the concept of Uniformitarianism, would you consider the earth to be very OLD or very YOUNG? 9

9 II my earth science class. I will get an A on my exams and quizzes. Discuss with a friend: 1.Describe the differences between catastrophism and uniformitarianism. catastrophism and uniformitarianism. 2. Provide at least 2 examples each of catastrophism and uniformitarianism. catastrophism and uniformitarianism. 3. Identify problems with both philosophies. 10

10 Relative Dating - placing the geologic occurrence in the proper sequence Relative Dating - placing the geologic occurrence in the proper sequence Which came first and WHY? To construct a relative time scale, rules were To construct a relative time scale, rules were established (principles of relative dating). established (principles of relative dating). Nicholas Steno ( ) Nicholas Steno ( ) Principle of Original Horizontality Principle of Original Horizontality Law of Superposition Law of Superposition Principle of Cross-Cutting Relations Principle of Cross-Cutting Relations Principle of Inclusions Principle of Inclusions Which came first and WHY? To construct a relative time scale, rules were To construct a relative time scale, rules were established (principles of relative dating). established (principles of relative dating). Nicholas Steno ( ) Nicholas Steno ( ) Principle of Original Horizontality Principle of Original Horizontality Law of Superposition Law of Superposition Principle of Cross-Cutting Relations Principle of Cross-Cutting Relations Principle of Inclusions Principle of Inclusions 11

11 Lets unravel some geologic history from observations of various formations and their contacts. Nicholas Steno – 1669 proposed the following relative dating principles: The Principle of Original Horizontality: Sedimentary rock layers are deposited as horizontal strata. Any observed non-horizontal strata have been disturbed. basin Sediment input A A B B C C 12

12 Limestone (ls) Shale (sh) Sandstone (ss) granitic rock Original Horizontal Strata 13

13 The Principle of Superposition In any undisturbed sequence of strata, the oldest stratum is at the bottom of the sequence, and the youngest stratum is on top. is on top. The Principle of Superposition In any undisturbed sequence of strata, the oldest stratum is at the bottom of the sequence, and the youngest stratum is on top. is on top Unit 1 = old Unit 5 = young Unit 1 = old Unit 5 = young 14

14 Which strata is older? oldest youngest 15

15 The principle of Cross-Cutting Relationships Any geologic feature that cuts across another geologic feature is younger.Any geologic feature that cuts across another geologic feature is younger. The principle of Cross-Cutting Relationships Any geologic feature that cuts across another geologic feature is younger.Any geologic feature that cuts across another geologic feature is younger Unit 1 = older Unit 6 = youngest Unit 1 = older Unit 6 = youngest Which came first: Unit 5 or Unit 6? Which came first: Unit 5 or Unit 6? 16

16 Which is older, the fault or volcanic layer? Which is older, the fault or volcanic layer? Volcanic layer fault What type of fault is this? What type of fault is this? Which is younger, the dike or country rock? Which is younger, the dike or country rock? country rock dike Determine the relative age of the two dikes Normal 17

17 The Principle of Inclusions A piece of rock (clast) that has become includedA piece of rock (clast) that has become included in another rock body is older than the rock body in another rock body is older than the rock body it has become part of – why? it has become part of – why? Rock body A Intrusion of pluton B A A A Older (Rock A was there first.) 18

18 Which granites are older and younger? OLDER YOUNGER 19

19 Which rock body is older?: A A B B C C ? ? ? ? Can you identify the inclusions found in this Sierra Nevada Mountain batholitic material? Can you identify the inclusions found in this Sierra Nevada Mountain batholitic material? 20

20 Youngest Oldest Superposition Original Horizontality Cross-Cutting Relationship ABCAsp Vn Principle of Inclusions Principle of Inclusions Which granite is older? Older Younger 21

21 II this earth science class. I will get an A on my exams and quizzes. Discuss with a friend: 4. Explain the concept of relative dating. 5. Draw a diagram, and explain each of the following dating principles: following dating principles: Original Horizontality Superposition Cross-Cutting Relations Inclusion Principle Inclusion Principle 4. Explain the concept of relative dating. 5. Draw a diagram, and explain each of the following dating principles: following dating principles: Original Horizontality Superposition Cross-Cutting Relations Inclusion Principle Inclusion Principle 22

22 Ok – given the principles, what is wrong with this stack of rock (strata) Missing time – or does time really stop? oldest youngest 23

23 The principle of Unconformities rock surface that represents a period of erosion or non- depositionrock surface that represents a period of erosion or non- deposition referred to as missing timereferred to as missing time three major types of unconformities:three major types of unconformities: disconformitydisconformity angular unconformityangular unconformity non-conformitynon-conformity Unconformity disconformityunconformity in non-disturbed disconformity – unconformity in non-disturbed sedimentary layers sedimentary layers angular unconformity – uncon. lies between angled strata and overlying strata and overlying horizontal strata horizontal strata non-conformity – sedimentary strata overlies crystalline overlies crystalline rocks (ig and met) rocks (ig and met) Igneous or metamorphic rock 24

24 Xln rocks Sedimentary rocks disconformity angular unconformity angular unconformity nonconformity 25

25 II this earth science class. I will get an A on my exams and quizzes Discuss with a friend 6. Explain what an unconformity is and what it represents. what it represents. 7. Diagram pictures that represent the three types of unconformities. three types of unconformities. 26

26 Fossils – evidence of past life or time pieces, the remains or traces of prehistoric life Paleontology – study of fossils How do we get a fossil? – preservation of past life 2 conditions must exist for preservation 2 conditions must exist for preservation rapid burial rapid burial possession of hard parts possession of hard parts Prehistoric bug Bug diesBug soft parts are eaten or dissolve Rapid burial of sediment covers the bug – fossil 27

27 Fossils – evidence of past life or time pieces, the remains or traces of prehistoric life Preservation of fossils Small percentage of fossils preserved throughout geologic time – WHY? Most organisms composed of soft parts. Organisms with hard parts and within a sedimentary environment are favored. Very rare to see vast array of other life forms How do fossils help scientists relatively date layers of rock (strata)? 28

28 William Smith – Principle of Fossil Succession Fossil organisms succeed one another in a definite and determinable order, and therefore any time period can be recognized by its fossil content. Fossils are arranged according to their age by using the law of superposition. Fossil succession: allows geologists to age date wide geographical areas areas documents the evolution of life Age of mammals Age of reptiles Age of fish Oldest Youngest 29

29 How do fossils help date rocks? 1200 miles Which fossils are the youngest and oldest? Disconformity

30 31

31 II this earth science class. I will get an A on my exams and quizzes. Discuss with a friend: 8. Give 2 reasons why many organisms are are not fossilized. are not fossilized. 9. Explain the law of fossil succession and how this law allows dating of strata. how this law allows dating of strata. 10. How has fossil succession helped geologists unravel earth history? geologists unravel earth history?

32 OK – We have relative dating and fossils – How do we get absolute ages on the rocks (numbers)? Radiometric dating – applying a number radioactive atoms (isotopes) decay at a constant rate over time 33

33 Radioactive decay of an unstable isotope atom Decay process The time of decay can be measured. Isotope decay does not vary under various weathering conditions. Isotopes decay at a fixed rate. One isotope will decay into another isotope. The time of decay can be measured. Isotope decay does not vary under various weathering conditions. Isotopes decay at a fixed rate. One isotope will decay into another isotope. U 238 (Uranium) Pb 206 (lead) 34

34 How does radiometric dating work, and where does the age (number) come from? Half life: the time required for ½ of the parent to decay into the daughter element Parent element: the beginning element that contains 100% of radioactive particles Daughter element: the element that the parent element decays into (or turns into over time) Parent Isotope Stable Daughter Product Currently Accepted Half-Life Values Uranium-238Lead billion years Uranium-235Lead million years Thorium-232Lead billion years Rubidium-87Strontium billion years Potassium-40Argon billion years Samarium-147Neodymium billion years Terms: 35

35 U-3 U-235Pb m.y. 1.4 b.y. 2.1 b.y. 1 half life = 704 million years 1/21/41/8 Daughter element Parent element 36

36 II this earth science class. I will get an A on my exams and quizzes. 11. Specifically define the differences between relative and absolute dating between relative and absolute dating techniques. techniques. 12. Define the following absolute dating terms parent/daughter elements, half-life terms parent/daughter elements, half-life 13. Explain how the half-life is used to calculate an absolute age. calculate an absolute age. 37

37 What is the importance of radiometric dating? produced thousands of dates for earth events rocks have been dated at more than 3 b.y. granite in South Africa dated at 3.2 b.y. granite contains inclusions of quartzite quartzite inclusions must be older Acasta gneiss in Northern Canada – 4.0 b.y. Earth believed to be 4.55 (4.6) b.y. old Radiometric dating: vindicated the ideas of Hutton, Darwin, and others consistent with relative dating techniques allowed absolute dating on the Geologic Time Scale 38

38 Lets make a Geologic Time Scale The Geologic Time Scale: It combines both relative and absolute dating Created during the nineteenth century in Western Europe and Great Britain Sub-divides the 4.6 billion-year-history of the earth Eons Eras Periods Epochs Relative dating + Absolute dating 39

39 Hadean represents the earths time of formation no rocks are represented hellish conditions Hadean represents the earths time of formation no rocks are represented hellish conditions Archean Single cell life developed most ancient rocks found preserved rocks at the base of the Archean Archean Single cell life developed most ancient rocks found preserved rocks at the base of the Archean Proterozoic Multi-celled, soft body organisms early life Proterozoic Multi-celled, soft body organisms early life Precambrian Phanerozoic visible life fossil record becomes more detailed animals have hard shells and skeletons Phanerozoic visible life fossil record becomes more detailed animals have hard shells and skeletons Building the Geologic Time Scale 40

40 Paleozoic Era known as ancient life life progressed from marine invertebrates to fish, amphibians, and reptiles Paleozoic Era known as ancient life life progressed from marine invertebrates to fish, amphibians, and reptiles Mesozoic Era marks the rise in dinosaurs dominant vertebrates first flowering plants first shrew-like mammals Mesozoic Era marks the rise in dinosaurs dominant vertebrates first flowering plants first shrew-like mammals Cenozoic Era birds and mammals flourished appearance of man Cenozoic Era birds and mammals flourished appearance of man 41

41 Periods based on: fossil types massive extinctions geographical locations characteristics of strata Periods based on: fossil types massive extinctions geographical locations characteristics of strata Cambrian period animals with hard shells diversification of life the Cambrian explosion Cambrian period animals with hard shells diversification of life the Cambrian explosion Cretaceous, Jurassic, Triassic age of reptiles dinosaurs dominant massive dinosaur extinction at 65 m.y. –Cretaceous Jurassic Park Cretaceous, Jurassic, Triassic age of reptiles dinosaurs dominant massive dinosaur extinction at 65 m.y. –Cretaceous Jurassic Park 42

42 Epochs not defined by extinction events, but % of fossils still living plants and animals found in the Pliocene epoch have living species today Eocene-few species surviving today Holocene humans time Epochs not defined by extinction events, but % of fossils still living plants and animals found in the Pliocene epoch have living species today Eocene-few species surviving today Holocene humans time Age of Reptiles Amphibians Age of fish Invertebrates How accurate is the Geologic Time Scale? How accurate is the Geologic Time Scale? 43

43 II the Geologic Time Scale. 14. You should be able to draw the Geologic Time Scale and label it with the following: Time Scale and label it with the following: Eons, Eras, Periods, and Cenozoic/ Tertiary epochs. Tertiary epochs. 15. List major characteristics of each period. period. 16. How did the strength of both absolute and relative dating techniques contribute the relative dating techniques contribute the development of the geologic time scale? development of the geologic time scale? 44

44 Cenozoic, Mesozoic, Paleozoic Eras The Geologic Time Scale – How much of Earth history is represented? 12% Precambrian Eon 88% Geologic Time Scale 45

45 Difficulties in dating the Geologic Time Scale Not all rocks can be dated radiometrically. Not all rocks can be dated radiometrically. all minerals must contain 100% parent atoms. all minerals must contain 100% parent atoms. Sedimentary rocks can only rarely be dated. Sedimentary rocks can only rarely be dated. some parent atoms come from pre-existing rocks some parent atoms come from pre-existing rocks that have been weathered and transported. that have been weathered and transported. sedimentary rocks are dated in proximity of sedimentary rocks are dated in proximity of igneous bodies. igneous bodies. Metamorphic rocks are challenging. Metamorphic rocks are challenging. some minerals do not necessarily represent the some minerals do not necessarily represent the time when the rock was formed time when the rock was formed 46

46 How is the age of the Earth determined? Why is it difficult to determine the age of the earth? (think rock cycle) The external and internal forces constantly recycle earth material, obliterating rock clues to the earths past. Why is it difficult to determine the age of the earth? (think rock cycle) The external and internal forces constantly recycle earth material, obliterating rock clues to the earths past. What evidence suggests a 4.6 b.y. old earth? Precambrian rocks (Acasta gneiss, northern Canada) date at 4.0 billion years. Mineral grain found in sedimentary rock (Australia) dates at 4.4 billion years. What does the mineral grain in a sedimentary rock indicate about the 4.4 b.y. age relationship? Precambrian rocks (Acasta gneiss, northern Canada) date at 4.0 billion years. Mineral grain found in sedimentary rock (Australia) dates at 4.4 billion years. What does the mineral grain in a sedimentary rock indicate about the 4.4 b.y. age relationship? 47

47 Acasta gneiss, northern Canada known as the Acasta gneiss complex dated at the Hadean Eon (4.0 billion years old) part of the Canadian Slave craton Acasta gneiss, northern Canada known as the Acasta gneiss complex dated at the Hadean Eon (4.0 billion years old) part of the Canadian Slave craton 48

48 Evidence from space to age date the earth-- moon dust and meteorites: moon dust from Apollo astronauts dated at 4.55 billion years the Allende Meteorite: a carbonaceous chondrite meteorite that was found in Chihuahua, Mexico, 1969 contains unaltered material from the formation of the solar system composed of tiny amounts of carbon that form the compounds of amino acids (essential for life) age dating of this and other meteorites is around 4.55 billion years based on earth rocks and interstellar space objects, earth is believed to be around 4.6 billion years old. moon dust and meteorites: moon dust from Apollo astronauts dated at 4.55 billion years the Allende Meteorite: a carbonaceous chondrite meteorite that was found in Chihuahua, Mexico, 1969 contains unaltered material from the formation of the solar system composed of tiny amounts of carbon that form the compounds of amino acids (essential for life) age dating of this and other meteorites is around 4.55 billion years based on earth rocks and interstellar space objects, earth is believed to be around 4.6 billion years old. 49

49 Allende Meteorite, Chihuahua, Mexico, Feb. 8, 1969 carbonaceous chondrite unaltered material from our solar system contains carbon (3 parts/1000) some carbon compounds in the form of amino acids dark areas – olivine with trace amounts of iron and carbon dark areas – olivine with trace amounts of iron and carbon calcium and aluminum oxide compounds first matter to form during solar system formation older than earth calcium and aluminum oxide compounds first matter to form during solar system formation older than earth 50

50 II what ES can do for me. I will get an A on my exams and quizzes. Discuss with a friend: 17. Identify at least 2 problems with the accuracy of the Geologic Time Scale. accuracy of the Geologic Time Scale. 18. Why does the Geologic Time Scale only represent about 12% of the earths geologic represent about 12% of the earths geologic history (assuming the earth is 4.6 b.y. old)? history (assuming the earth is 4.6 b.y. old)? 51


Download ppt "Geologic Time 1. Which geologic event took place first and when? when? Which rock layer is older, and how is earth Which rock layer is older, and how."

Similar presentations


Ads by Google