Start movie at present and go back in time. … 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 last 2 millennia (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!

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

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

Still being refined as more information becomes available Geologic Time and the "geologic column" Geologic Time and the "geologic column" • • Developed using logical rules to establish relative sequences of events 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 • • 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

The Geologic Time Scale (1:2)

The Geologic Time Scale (2:2)

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

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.

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.

Age Estimates of Earth Counting lifetimes in preserved texts Comparing cooling rates of minerals. 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!

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. + + 235 40 14

unstable nuclei in parent isotope emits 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.

Rate of Decay t All atoms are parent isotope or some 1 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) 2 2 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 isotope (1.5 parent: 10.5 daughter) We would see the rock at this point.

100 % parent remaining Parent Parent Daughter Daughter 50 25 13 Radioactive Isotopes Radioactive Isotopes • • analogous to sand in an hour glass analogous to sand in an hour glass - - we measure how much sand there is we measure how much sand there is > > represents the represents the mass of elements mass of elements - - we measure the ratio of sand in the bottom to sand in the top we 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 bottom we know at what rate the sand falls into the bottom > > the half life of the radioactive element the half life of the radioactive element - - how long would it take to get the amount sand in the observed how long would it take to get the amount sand in the observed ratio starting with all of it in the top? ratio starting with all of it in the top? 100 Parent Parent % parent remaining Daughter Daughter 50 25 13 time----------->

Five Radioactive Isotope Pairs Five Radioactive Isotope Pairs Effective Dating Range Minerals and Isotopes Half-Life of Parent (Years) Rocks That Can Parent Daughter (Years) Be Dated Uranium 238 Lead 206 4.5 billion 10 million to Zircon 4.6 billion Uraninite Uranium 235 Lead 207 704 million Muscovite Thorium 232 Lead 208 14 billion 48.8 billion Biotite Potassium feldspar Rubidium 87 Strontium 87 4.6 billion 10 million to Whole metamorphic 4.6 billion or igneous rock Potassium 40 Argon 40 1.3 billion 100,000 to Glauconite 4.6 billion Muscovite Biotite Hornblende Whole volcanic rock

Carbon-14 dating is based on the Carbon-14 dating is based on the Radiocarbon and Tree- Ring Dating Methods Carbon-14 dating is based on the Carbon-14 dating is based on the • • ratio of C-14 to C-12 ratio of C-14 to C-12 in an organic sample. sample. > > Valid only for samples less than 70,000 Valid only for samples less than 70,000 years old. years old. > > Living things take in both isotopes of Living things take in both isotopes of carbon. 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

Carbon 14 Cycle

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)

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

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

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

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 won’t show up at typical map scales Groups have formations; formations have members