Today 10 Geologic principles (abridged) Part III Earth s Changing Landscapes Geography 101 Physical Geography: Earth s Surface Landscapes M. Pesses, Antelope Valley College The Rock Cycle Geology Basics Earth s crust 8 main elements Minerals Bonded elements with a crystalline structure The building blocks of rocks Minerals Amethyst (SiO 2 ) An assemblage of minerals Granite Rocks Quartz, feldspar, mica, hornblende Categories Igneous Processes All rocks can be sorted into one of three categories Igneous Sedimentary Metamorphic Forms when magma or lava solidifies Magma Molten rock underneath surface of the Earth Lava When magma reaches surface of the Earth Instructor: Pesses 1
Intrusive Igneous Rocks Intrusive Igneous Rocks Term for rock formed by cooling magma Magma fills in cracks Slow cooling Large grain size Granite Mass of intrusive rock called pluton Large pluton called a batholith Intrusive igneous rocks also called plutonic rocks Extrusive Igneous Rocks Rocks formed by cooling lava Cools quickly Fine grained Also called volcanic rocks Granite Basalt Intrusive Medium to coarse grained Felsic Rich in feldspar and silica Extrusive Fine grained Mafic Rich in iron and magnesium Makes up most of ocean floor Instructor: Pesses 2
Sedimentary Rocks Made from layering of broken down rock & mineral particles Sometimes organic material Subclasses 1. Clastic 2. Chemically Precipitated 3. Organic Sedimentary Rocks Examples Clastic Made of fragments of rock & minerals Layering Sedimentary Rocks Chemically precipitated Dissolved minerals or hard parts of organisms Transported in solution, then precipitated Evaporites Water evaporates, leaves salt Death Valley, after rain Death Valley, after water evaporates Instructor: Pesses 3
Organic Sedimentary Rocks Hydrocarbons Sediment made from decaying animal & plant tissue Solid Coal, Peat Liquid Petroleum Gas Natural gas Fossils Almost Exclusively in Sedimentary Rocks Heat of Melting or Metamorphism Would Destroy Almost Every Type of Fossil Buried Rapidly After Death, Preserved From Decay Environmental Clues Fossils Salt Water Corals, Echinoderms Fresh Water Insects, Amphibians Terrestrial Leaves, Land Animals Color & Chemistry Red Beds Often Terrestrial Black Shale Oxygen Poor, Often Deep Water Evaporites Arid Climates Stratification Metamporphic Processes Usually present in Sedimentary Rocks Originally Horizontal Variations in Deposition Changes in sedimentary or igneous rock due to heat or pressure Radioactive decay Pressure deep within Earth Instructor: Pesses 4
Foliation Mineral structure demonstrates a particular alignment after metamorphism Quartzite (formerly Sandstone) not foliated Slate (formerly Shale) foliated Geology An evolving science The Theory of Plate Tectonics was just initially accepted in the 1960's. Physical geology The study of Earth s mineral & rock materials Geology Historical geology Studying the origins and evolution of the planet itself Geology Instructor: Pesses 5
Human scale Longitude Railroad schedules Daylight Savings Time Time 1769 Watts develops the steam engine Industry begins Raw materials are needed Food in England White Bread, Roast Beef Leisure time to think (instead of survival) Revolution Revolution Societal change postal system in England The country is connected Non traditional students Contemplation on origins of everything Not anti god, but not pro church officials either Irish archbishop Dated the Earth to beginning Sunday, October 23, 4004 BC Annals of the Old Testament, 1650 Young Earth James Ussher Early Thought Early Thought Catastrophism A belief that Earth s dramatic landforms were created by short lived, catastrophic events Allows for young Earth concept Geology sought the origin of the Earth Church answers were not answering everything Pound stones Instructor: Pesses 6
1726 1797 Earth couldn t be so young A continuous cycle with no vestige of a beginning, no prospect of an end. James Hutton Uniformitarianism James Hutton The same processes active today have been occurring throughout geologic time These processes are almost invisible to us, but unbelievably powerful An ancient, dynamic Earth Charles Lyell James Hutton Principles of Geology, 1830 Charles Darwin The Origin of Species, 1859 It does not mean: Uniformitarianism Catastrophes never occur Physical Conditions on Earth never Change Physical processes always occur at the same rate or intensity Geologic Time 15 billion years = 15,000,000,000 years 15 billion seconds = 475 years Considering 1 second to correspond to 1 year: Big Bang A.D. 1526 Earth s Formation 1858 Dinosaurs lived from 1993 1999 Humans appeared 2 weeks ago Ice Ages would have happened every day for the last 2 weeks. The last one would have ended 5 hours ago Julius Caesar lived 44 minutes ago United States created just over 3 ½ minutes ago World War II ended 56 seconds ago Instructor: Pesses 7
Some Geologic Rates Cutting of the Grand Cyn. 1 cm/15 yr Uplift of the Alps 1 cm/20 yr Movement of the San Andreas Fault 5 cm/yr Dating Two ways to figure out how old something is: 1. Relative dating 2. Absolute dating Examples Relative George W. Bush was president before Barack Obama Relative Dating In the absence of absolute dates, putting geologic events into order (oldest to youngest) Absolute George W. Bush in office January 20, 2001 January 20, 2009 Barack Obama in office starting January 20, 2009 Relative Dating Principle of Original Horizontality Sedimentary units and lava flows are deposited horizontally. Principle of Superposition Relative Dating The layer below is older than the layer above. Instructor: Pesses 8
Relative Dating Uplift & tilting occurs after rock layers are formed Principle of Crosscutting Relationships A rock is younger than any rock across which it cuts. From James Hutton Relative Dating Occam s Razor The simplest explanation is always preferred Doesn t guarantee that things must be simple! Parsimony Theories with unsupported ideas are probably wrong. Interpreting Data This? Or This? Steven Dutch Steven Dutch Instructor: Pesses 9
Implications The laws of nature are the same throughout the universe Either: The laws of nature change but just happen to produce effects that look like the presently known laws of nature or The laws of nature really are the same everywhere Implications We live in a universe of patterns If someone claims there is an exception to a known pattern, the simplest explanation is that he/she is wrong The burden of proof in science is on the challenger Absolute Dating Absolute Dating While relative dates are useful, an exact date is always better. Just how old is the Earth? Radiometric dating Radioactive decay of elements in minerals can be consistently measured Change to different element Half life How it works As an element ages, it decays This releases energy and subatomic particles The resulting decay product is a different element How it works Example: Postassium 40 decays & changes to Argon 40 The radioactive isotope which undergoes decay is called the parent element (like potassium). The parent element undergoes radioactive decay to form a daughter element (like argon). Instructor: Pesses 10
Half-Life Carbon Dating? Next Time Same concept Decay of Carbon 14 Used with organic remains Plate Tectonics Pangaea Instructor: Pesses 11