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Geological Time - really, really, really long! Motion pictures are generally projected at 32 frames per second. Therefore, each frame (image) is on the.

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Presentation on theme: "Geological Time - really, really, really long! Motion pictures are generally projected at 32 frames per second. Therefore, each frame (image) is on the."— Presentation transcript:

1 Geological Time - really, really, really long! Motion pictures are generally projected at 32 frames per second. Therefore, each frame (image) is on the screen for only split second- let each frame represent 100 years. Start movie at present and go back in time. The Declaration of Independence would show up 1/16 of a second into the movie. The Christian era (BC-AD boundary) would be 3/4 of a second into the movie. The most recent Ice Age would be 7 seconds into it. The movie would run about 6 hours before we got to the end of the Mesozoic era (extinction of the dinosaurs). We'd have to watch the movie for about 2 days to see the beginning of the Paleozoic era (macroscopic life). The whole movie (to the beginning of geologic time on Earth) would be approximately 16 days long! Motion pictures are generally projected at 32 frames per second. Therefore, each frame (image) is on the screen for only split second- let each frame represent 100 years. Start movie at present and go back in time. The Declaration of Independence would show up 1/16 of a second into the movie. The Christian era (BC-AD boundary) would be 3/4 of a second into the movie. The most recent Ice Age would be 7 seconds into it. The movie would run about 6 hours before we got to the end of the Mesozoic era (extinction of the dinosaurs). We'd have to watch the movie for about 2 days to see the beginning of the Paleozoic era (macroscopic life). The whole movie (to the beginning of geologic time on Earth) would be approximately 16 days long!

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3 > Relative: Placing events in a sequence based on their positions in the geologic record. > Chronologic sample. Two ways to relate time in geology: > Relative: Placing events in a sequence based on their positions in the geologic record. > Chronologic : Placing a specific number of years on an event or rock sample. Geologic Time

4 Geologic Time Scale a combination of the two types of age determinations > > a a relative sequence of lithologic units - - established using logical principles > > measured against a framework of chronologic dates.

5 Geologic Time and the "geologic column" Developed using logical rules to establish relative sequences of events refined - - Geologic Time and the "geologic column" Developed using logical rules to establish relative sequences of events - superposition - cross-cutting relationships - original horizontality - lateral continuity Added to as new information is obtained and data is refined - Use of fossils for correlation and age determination Numerical Dates attached to strata after the development of Radiometric techniques - Still being refined as more information becomes available

6 The Geologic Time Scale (1:2)

7 The Geologic Time Scale (2:2)

8 Relative Dating Methods determines the relative sequence of events. > > which came first, which came last. > > no numeric age assigned 6 Relative age principles: > > Superposition > > Original Horizontality, > > Lateral continuity > > Cross-cutting Relationships > > Inclusions > > Fossil succession. Those in yellow are most useful

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10 Law of Superposition In undisturbed strata, the layer on the bottom is In undisturbed strata, the layer on the bottom is oldest, those above are younger.

11 Original Horizontality Sediments are generally deposited as horizontal layers. Lateral Continuity Sediment layers extend laterally in all direction until they thin & pinch out as they meet the edge of the depositional basin. they meet the edge of the depositional basin.

12 included description and use of Charles Lyell - >principles of cross-cutting relationships >principles of inclusions relative time tools Charles Lyell 1st Principles of Geology text - >principles of cross-cutting relationships >principles of inclusions relative time tools

13 Cross-cutting Relationships That which cuts through is younger than the Object that is cut dike cuts through granite is cut

14 Relative Ages of Lava Flows and Sills

15 Principle of Inclusions Inclusions (one rock type contained in another rock type) are older than the rock they are embedded in. That is, the younger rock contains the inclusions

16 Principle of Inclusions

17 Faunal/Floral Succession Fossil assemblages (groupings of fossils) succeed one another through time.

18 Correlation- relating rocks in one location to those in another using relative age stratigraphic principles - - Superposition - - Lateral Continuity - - Faunal Succession - - Cross-cutting

19 Unconformities surfaces represent a long time. a time when rocks were not deposited or a time when rocks were eroded Hiatus the gap in time represented in the rocks by an uncon- formity 3 kinds Angular Unconformity Nonconformity Disconformity

20 Disconformities A surface of erosion or non-deposition between Parallel sedimentary rock beds of differing ages.

21 Angular Unconformities An angular unconformity is an erosional surface on tilted or folded strata, over which younger strata have been deposited.

22 Nonconformities A nonconformity is an erosional surface on igneous or metamorphic rocks which are overlain by sedimentary rocks.

23 Breakout in to groups and discuss the sequence observed here

24 Age Estimates of Earth Counting lifetimes in the Bible Comparing cooling rates of iron pellets. Determine sedimentation rates & compare Estimate age based on salinity of the ocean. all age estimates were off by billions of years some were more off than others!

25 > + Absolute Dating Methods Radioactive Decay sequences acts as an atomic clock we see the clock at the end of its cycle analogous to starting a stopwatch allows assignment of numerical dates to rocks. > + decay ) into Radioactive isotopes change ( daughter isotopes at known rates. rates vary with the isotope e.g., U, K, C, etc

26 Decay unstable nuclei in parent isotope emits subatomic particles and transform into another isotopic element (daughter). does so at a known rate, measured in the lab Half-life The amount of time needed for one-half of a radioactive parent to decay into daughter isotope. Assumptions?-you bet Cross-checks ensure validity of method. Assumptions?-you bet Cross-checks ensure validity of method.

27 Rate of Decay t t 0 0 t t 1 1 t t 3 3 All atoms are parent isotope or some known ratio of parent to daughter 1 half-life period has elapsed, half of the material has changed to a daughter isotope (6 parent: 6 daughter) t t half-lives elapsed, half of the parent remaining is transformed into a daughter isotope (3 parent: 9 daughter) 3 half-lives elapsed, half of the parent remaining is transformed into a daughter isotope (1.5 parent: 10.5 daughter) We would see the rock at this point.

28 Radioactive Isotopes analogous to sand in an hour glass - we measure how much sand there is >represents themass of elements - we measure the ratio of sand in the bottom to sand in the top - at the end (present) >daughter (b) and parent (t) - we know at what rate the sand falls into the bottom >the half life of the radioactive element - how long would it take to get the amount sand in the observed ratio starting with all of it in the top? Radioactive Isotopes analogous to sand in an hour glass - we measure how much sand there is >represents themass of elements - we measure the ratio of sand in the bottom to sand in the top - at the end (present) >daughter (b) and parent (t) - we know at what rate the sand falls into the bottom >the half life of the radioactive element - how long would it take to get the amount sand in the observed ratio starting with all of it in the top? time > Parent Daughter Parent Daughter % parent remaining

29 Five Radioactive Isotope Pairs Half-Life EffectiveMinerals and Isotopes of Parent Dating Range Rocks That Can ParentDaughter (Years) Be Dated Uranium 238Lead billion10 million toZircon 4.6 billionUraninite Uranium 235Lead million Thorium 232Lead billion48.8 billion Rubidium 87Strontium billion10 million to Muscovite Biotite Potassium feldspar Whole metamorphic or igneous rock Potassium 40Argon billion100,000 toGlauconite 4.6 billionMuscovite Biotite Hornblende Whole volcanic rock (Years) 4.6 billion

30 Radiocarbon and Tree- Ring Dating Methods Carbon-14 dating is based on the ratio of C-14 to C-12 sample. > Valid only for samples less than 70,000 years old. > Living things take in both isotopes of carbon. > When the organism dies, the "clock" starts. Carbon-14 dating is based on the ratio of C-14 to C-12 in an organic sample. > Valid only for samples less than 70,000 years old. > Living things take in both isotopes of carbon. > When the organism dies, the "clock" starts. Method can be validated by cross-checking with tree rings

31 Carbon 14 Cycle

32 Recognizing Patterns of change Walther's Law The vertical sequence is repeated by the horizontal sequence - - walking from A to B to C to the Coast you would encounter the rocks that would be encountered by drilling a core into the earth at any point (A, B, or C)

33 Facies Diagram distribution of lithofacies (rock-types) - - these are associated with their respective EOD biofacies are similar but refer to fossils rather than rock types

34 Eustasy, relative sea-level, and relative position of lithofacies Eustasy= changes in volume of water in ocean lithofacies depend on - sea-level - land level - geometry of coast - sediment supply Vail Curve an attempt at global correlation of lithologies - for better production - of petroleum resources

35 Rock designations Rock units called Lithostratigraphic units - - described in terms of Group, Formation, & Member > > each term has specific meanings in geological parlance Formation - - a mappable lithostratigraphic unit > > has a location for identifying the type-section > > has a rock designation describing the lithology - - sometimes not all the same lithology > > in which case the term "Formation" takes the place of lithologic type Groups are composed of several formations Members are distinctive units within a formation - - group is largest and contains formations and members - - formations are next and contain members Rock designations Rock units called Lithostratigraphic units - - described in terms of Group, Formation, & Member > > each term has specific meanings in geological parlance Formation - - a mappable lithostratigraphic unit > > has a location for identifying the type-section > > has a rock designation describing the lithology - - sometimes not all the same lithology > > in which case the term "Formation" takes the place of lithologic type Groups are composed of several formations Members are distinctive units within a formation - - group is largest and contains formations and members - - formations are next and contain members

36 Fundamental lithological units Formation- a rock layer with distinctive characteristics that is mappable over a large are at typical map scales 1:62,500 or more commonly 1:24,000 Formations have Members smaller layers that are unique that are not mappable over larger areas and wont show up at typical map scales Fundamental lithological units Formation- a rock layer with distinctive characteristics that is mappable over a large are at typical map scales 1:62,500 or more commonly 1:24,000 Formations have Members smaller layers that are unique that are not mappable over larger areas and wont show up at typical map scales Groups have formations; formations have members


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