GEO 102 1st EditionExam # 2 Study Guide Lectures: 12-21Lecture 12 (September 22)Correlation-Linking time-equal rocks-Presently many different depositional environments form simultaneously.-Later they will be preserved incompletely as a wide range of rocksHow do you link the outcrops?-Rock types-Geochemistry-Fossils-Fossil succession-Fossils change in an orderly way through time-Index fossils-Extinction and evolution-Absolute datingAbsolute dating-Relative dating has been around centuries, and, but absolute estimates of the age of theEarth varied.-The goal was a fixed and absolute age-Radioactivity can act as a clock Decay and Half-life-Unstable nuclei eject particles predictably in order to achieve equilibrium-alpha particles ()-2 protons and 2 neutrons-beta particles ()-Electron from nucleus-Electron capture-Forms a neutron after fusing with a protonHalf-Life-For any given atom, it can not be predicted when decay will occur-However, a POPULATION of atoms will decay like clockwork-the time it takes for half of the population to decay = one half-lifeWhat do we date?-Only some elements have radioactive isotopes-Only some isotopes have half-lives that are useful-Only some minerals contain these few isotopes-Only some rocks contain pristine minerals-There must be no non-radioactive alteration of parent or daughter-Closed systemLecture 13 (September 24) Radio-isotopes-There are many isotope systems-Each has important differences-Half life-Mineral hosts-Abundances-Decay pathways-OriginsLecture 14 (September 26)Minerals to Rocks- Minerals form rockso Some are simple with one mineralo Others are complex with many mineralsRock Types- Igneouso From magma or lava- Metamorphico Altered through and/or pressure- Sedimentaryo Reformed bits of other rocks, broken down or from a solution- Rocks linked to tectonicsSo why the differences?- Time- Energy- Distance- MineralsTransitions- Parent rock to sediment, sediment to sedimentary rockTypes of Sedimentary Rocks- Clastic: a sedimentary rock made from pieces of pre-existing rock that weathered and erodedo Also called detrital- Chemical: sedimentary rock derived from minerals that precipitate from a fluid (often water)Lecture 15 (September 29)Types of Physical Weathering- Frost wedging- ice gets into a crack of a rock, expands, and breaks the rock- Unloading- exfoliation- Biological- from tree roots and fungi- Current/glacial- Thermal effectsTypes of Chemical Weathering- Dissolution- dropping acid o minerals. It dissolves the mineral away- Hydrolysis- electrochemically plucking molecules of a mineral out of the mineral- Oxidation- oxygen displacing a portion of the molecules in metal rich rocko Clays do not form initially as clay. Clay minerals only form as the residual broken down stuff of another mineral breaking downErosion- The transport of materials weathered from a rock- The principle agents are:o Liquid water (the most common)o Ice (rare but very effective)o Wind (only small particles)Entrainment- This refers to the act of lifting a particle from a position of rest to be carried in a wind or current- We can predict how this will happen with great precision using mathOrder of Transport- Heavy particles need a lot of energy to lift and carry- Clay needs a lot of energy to lift (van der waals forces) but very little to carry it- Particles are lifted in the following order:o Silt, sand, pebbles, and clay last- But they are dropped in a different ordero Pebbles, sand, silt, and clayLecture 16 (October 1)Life of a Rock- Let’s imagine how a parent rock (granite) becomes a series of daughter rocks (shale, sandstone, and siltstone)o Weatheringo Erosion o Sortingo Rounding o Deposition (different environments)o Lithification o UpliftSorting - The longer time and distance a sediment is transported the more it will sort according tomassRounding- The longer time and distance a sediment is transported the more it will round according to hardnessEnvironments of Deposition- Other signs of depositional environmentso Ripple markso Cross beddingo Larger debriso Desiccation cracks o Fossils o Chemistryo Mineralogy Lecture 17 (October 3)What is Ichnology?- Study of traces- Neoichnology- study of modern traces- Paleoichnology- study of fossil traces (trace fossils, ichnofossils) o Examples: footprints, tooth marks, nests, burrows, cocoons, and trailsThe Holy Trinity of Ichnology- Substrate- whatever is preserving the trace- Anatomy- Behavior- the living animal of the trace- One trace maker can make a variety of tracesPrehistory of Ichnology- Ichnology (as tracking) is among the oldest of sciences- Tracking developed and honed by indigenous peoples of Africa, Australia, and North AmericaWhat is it good for?- To date- They indicate certain ecosystems - Show animal or plant presence- Most traces are in place. That’s where the animal walked or where it was- Cultivates and expands awarenessLimits of Ichnology- Trace makers not always identified- Trace fossils might have been made by organisms with no modern analogue - Often do not co-occur with body fossils of trace makers- Potential for too much dataLecture 18 (October 6)Tectonics and Sediments- The distribution of all these processes is patterned based on plate tectonics- Uplift and long term preservation of these rocks is controlled to a great extent by plate tectonicso Think about California beaches as compared to Alabama beachesThe Rocks- Once sediments settle they may cement- The cement often comes from water with minerals in the solution- Compaction contributes to this Common Clastic Sedimentary Rocks- Conglomerateo Big clasts, poorly sorted,- Sandstoneo Smaller clasts, better sorting- Siltstoneo Tiny clasts, well sorted- Shaleo Nearly pure clay- Shale is the most common- Sandstone is the toughest- All are abundant in AlabamaChemical Sedimentary Rocks- What happens when you leave a glass of sweet tea in the fridge for too long?- What about when you don’t clean your bathtub often enough?- As a solution becomes more concentrated in a mineral it will solidify on an available surface- precipitation- Evaporates (salt)- Limestone- Chert - Dolostone- Coal?Organisms make many chemical sedimentary rocks- limestone- chert- coal?Coal- not really a rock- plant material- deposited in an anoxic environment (like a swamp or bottomland forest)- compactedLecture