Presentation on theme: "Geological Time - really, really, really long!"— Presentation transcript:
1Geological 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!
3Geologic Time • • Two ways to relate time in geology: > > RelativeRelative: Placing events in a: Placing events in asequence based on their positionssequence based on their positionsin the geologic record.in the geologic record.>>ChronologicChronologic: Placing a specificnumber of years on an event or rocksample.sample.
4Geologic Time Scale • a combination of the two types of age determinations>arelativesequence of lithologic units-established using logical principles>measured against a framework ofchronologicdates.
5Still being refined as more information becomes available Geologic Time and the "geologic column"Geologic Time and the "geologic column"••Developed using logical rules to establishrelative sequences of eventsDeveloped using logical rules to establish relativesequences of events--superposition--cross-cutting relationships--original horizontality--lateral continuityAdded to as new information is obtained anddata is refined••refinedUse of fossils for correlation and age determination--••Numerical Dates attached to strata after thedevelopment of Radiometric techniques--Still being refined as more informationbecomes available
8Relative 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
10Law of Superposition In undisturbed strata, the layer on the bottom is ••In undisturbed strata, the layer on the bottom isoldest, those above are younger.
11Original Horizontality ••Sediments are generally deposited ashorizontal layers.Lateral Continuity••Sediment layers extend laterally in alldirection until they thin & pinch out asthey meet the edge of the depositionalbasin.
12included description and use of Charles LyellCharles Lyell••1st Principles of Geology text--included description and use of>>principles of cross-cutting relationshipsprinciples of cross-cutting relationships>>principles of inclusionsprinciples of inclusions••relative time toolsrelative time tools
13Cross-cutting Relationships That which cuts through is younger than theObject that is cutdike cuts throughgranite is cut
17Faunal/Floral Succession ••Fossil assemblages (groupings of fossils)succeed one another through time.
18relating rocks in one location to those in • Correlation-relating rocks in one location to those inanother using relative age stratigraphicprinciples--Faunal Succession--SuperpositionLateral Continuity----Cross-cutting
19Unconformities • • surfaces represent a long time. Hiatus a time when rocks were notdeposited ora time when rocks wereerodedHiatusthe gap in time representedin the rocks by an uncon-formity3 kindsAngular UnconformityNonconformityDisconformity
20Disconformities A surface of erosion or non-deposition between Parallel sedimentary rock bedsof differing ages.
21Angular Unconformities Angular Unconformities •Anangular unconformityis an erosional surface on tiltedor folded strata, over which younger strata have been deposited.
22Nonconformities A nonconformity is an erosional surface on igneous or metamorphic rocks which are overlain by sedimentary rocks.
23Breakout in to groups and discuss the sequence observed here
24Age Estimates of Earth Counting lifetimes in the Bible Comparing cooling rates of iron pellets.Determine sedimentation rates & compareEstimate age based on salinity of the ocean.all age estimates were off by billions of yearssome were more off than others!
25Absolute Dating Methods RadioactiveDecay sequencesacts as an atomic clockwe see the clock at the end of its cycleanalogous to starting a stopwatchallows assignment of numerical dates torocks.>>decay) intoRadioactive isotopes change (daughter isotopes at known rates.rates vary with the isotopee.g., U , K , C, etc.++2354014
26unstable nuclei in parent isotope emits Decayunstable nuclei in parent isotope emitssubatomic particles and transform intoanother isotopic element (daughter).does so at a known rate, measured in thelabHalf-lifeThe amount of time needed for one-half of aradioactive parent to decay into daughterisotope.•Assumptions?-you betCross-checks ensure validity of method.
27Rate of Decay t All atoms are parent isotope or some 13All atoms are parent isotope or someknown ratio of parent to daughter1 half-life period has elapsed, half of thematerial has changed to a daughterisotope (6 parent: 6 daughter)22 half-lives elapsed, half of the parentremaining is transformed into a daughterisotope (3 parent: 9 daughter)3 half-lives elapsed, half of the parentisotope (1.5 parent: 10.5 daughter)We would see the rock at this point.
28100 % parent remaining Parent Parent Daughter Daughter 50 25 13 Radioactive IsotopesRadioactive Isotopes••analogous to sand in an hour glassanalogous to sand in an hour glass--we measure how much sand there iswe measure how much sand there is>>represents therepresents themass of elementsmass of elements--we measure the ratio of sand in the bottom to sand in the topwe measure the ratio of sand in the bottom to sand in the top--at the end (present)at the end (present)>>daughter (b) and parent (t)daughter (b) and parent (t)--we know at what rate the sand falls into the bottomwe know at what rate the sand falls into the bottom>>the half life of the radioactive elementthe half life of the radioactive element--how long would it take to get the amount sand in the observedhow long would it take to get the amount sand in the observedratio starting with all of it in the top?ratio starting with all of it in the top?100ParentParent% parent remainingDaughterDaughter502513time >
29Five Radioactive Isotope Pairs Five Radioactive Isotope Pairs EffectiveDating RangeMinerals andIsotopesHalf-Lifeof Parent(Years)Rocks That CanParentDaughter(Years)Be DatedUranium 238Lead 2064.5 billion10 million toZircon4.6 billionUraniniteUranium 235Lead 207704 millionMuscoviteThorium 232Lead 20814 billion48.8 billionBiotitePotassium feldsparRubidium 87Strontium 874.6 billion10 million toWhole metamorphic4.6 billionor igneous rockPotassium 40Argon 401.3 billion100,000 toGlauconite4.6 billionMuscoviteBiotiteHornblendeWhole volcanic rock
30Carbon-14 dating is based on the Carbon-14 dating is based on the Radiocarbon and Tree-Ring Dating MethodsCarbon-14 dating is based on theCarbon-14 dating is based on the••ratio of C-14 to C-12ratio of C-14 to C-12in an organicsample.sample.>>Valid only for samples less than 70,000Valid only for samples less than 70,000years old.years old.>>Living things take in both isotopes ofLiving things take in both isotopes ofcarbon.carbon.>>When the organism dies, the "clock" starts.When the organism dies, the "clock" starts.Method can be validated by cross-checking with tree rings
32Recognizing Patterns of change Walther's Law •The vertical sequence is repeated by the horizontalsequence-walking from A to B to C to the Coast you would encounter therocks that would be encountered by drilling a core into theearth at any point (A, B, or C)
33Facies Diagram • distribution of lithofacies (rock-types) • these are associated with their respective EOD•biofacies are similar but refer to fossils rather thanrock types
34Eustasy, relative sea-level, and relative position of lithofacies •Eustasy= changes in volume of water in oceanlithofacies depend on-sea-levelland levelgeometry of coastsediment supplyVail Curvean attempt at globalcorrelation oflithologiesfor better productionof petroleum resources
35Rock designations • Rock units called Lithostratigraphic units -described in terms of Group, Formation, & Member>each term has specific meanings in geological parlanceFormationa mappable lithostratigraphic unithas a location for identifying the type-sectionhas a rock designation describing the lithologysometimes not all the same lithologyin which case the term "Formation" takes the place of lithologictypeGroups are composed of several formationsMembers are distinctive units within a formationgroup is largest and contains formations and membersformations are next and contain members
36Fundamental lithological units Formation- a rock layer with distinctive characteristics that is mappable over a large are at “typical” map scales1:62,500 or more commonly 1:24,000Formations have Memberssmaller layers that are unique that are not mappable over larger areas and won’t show up at typical map scalesGroups have formations; formations have members