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!

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. 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.

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

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

Relative Ages of Lava Flows and Sills

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

Principle of Inclusions

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

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

Unconformities • • surfaces represent a long time. Hiatus 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

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

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

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

Breakout in to groups and discuss the sequence observed here

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!

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