Midterm 1 Material

What is science?-collection of facts that describe world around us-discovery the world is inherently understandable and we can understand it by observing it-creation of new knowledge

-knowledge what you accept as sufficiently real to take action upon and live your life-belief knowledge vs research knowledge-belief knowledge knowledge about world is inherent and unique in each human being-attained by individual revalation-i.e. supernatural personal belief not observable by others-research knowledge way of gathering knowledge that is universal, not individual-involves natural phenomena observable and measureable by multiple humans-repeatable-scientists make choice to believe in research knowledge methodology of science-belief knowledge cannot be used to comment on research knowledge and vice versa

-Facts a thing that is indisputably the case-belief and research knowledge both generate facts

How does science work?-science is a process-observations (data)-interpretations (hypothesis)-good science-hallmark of good science = doubt-good scientists question everything all the time-good science recognizes that new facts may terminate old ideas-also recognizes that observations are potentially biased-several theories can also be raised to explain one observation-willingness to accept uncertainty-bad science-science not infallible practiced by humans-humans can exhibit greed, malice, etc-ugly science-an attempt to borrow the clothing of science in order to cloak a message whose content is not based on science - pseudoscience

-how to spot pseudoscience-repeated reference to authority rather than observation-unwillingness to try to disprove own hypothesis or seek contradictory examples-consistent presentation of hypotheses in a simplistic manner-or in non-professional venues where success of argument equated with popularity of presentation -failure to add new arguments and data-consistent reliance on existing arguments-society and science-society cannot operate on science alone-research knowledge is without a value system-society and belief-society cannot operate on belief alone-many advancements in everyday life result of science

Prove/proof-don't prove a theory/hypothesis, try to falsify it-good hypothesis presented so that there is some experiment or possible discovery that could falsify it

Truth-truth is moral judgment, not scientific concept-science is constantly changing as old hypotheses are falsified and new ones take their place-hypotheses that have withstood many attempts at falsification are elevated to the rank of theory or even law-they are commonly thought of as true, although this may be incorrect use of the word true

Peer Review-people publishing articles scientist revise other scientists articles-hierarchy of journals = intensity of peer review-fame and glory can come from falsification of long standing hypotheses-einsteinObservation vs Interpretation-obervations facts that should be repeatable from one person to the next-interpretations hypotheses you invent to explain observations-subject to change with new observations

Minerals

-What is a rock? -an aggregate of minerals or mineraloids

Minerals-naturally occurring-inorganic solid-orderly internal structure-crystalline-crystal lattice

Identification of Minerals-characterize using chemical formula-determined by use of expensive machines-determine lattice spacing-xray defraction-xrays able to pass through crystal lattice

The silicate Minerals-silicates all contain silicon and oxygen-silicon and oxygen atoms are covalently bonded together-most common rock-forming minerals-silica oxygen tetrahedral-looking for other elements to bond with-common elements like Al, Fe, Mg, Ca, K, Na-and other Si-O tetrahedral

Individual tetrahedral-isolated SiO4 tetrahedra bond to cations-olivine green, found in volcanic rocks, decomposes/weathers quickly-silicon-oxygen ratio of 1:4

Chains-SiO4 tetrahedra bond together to form single chains-Silicon-oxygen ratio of 1:3-Pyroxene dark green/black

Double chains-SiO4 tetrahedra chain bonds to another chain to form double chains-silicon-oxygen ratio of 1:2.75-amphibole black

Sheets-SiO4 tetrahedra bond together to form sheets-silicon-oxygen ratio of 1:2.5-clay/micas-micas biotite/muscovite

FrameworkSiO4 bond together in all dimensions-silicon-oxygen ratio of 1:2-quartz/feldspar-feldspar most common mineral group

Other common non-silicate minerals-carbonates-minerals with CO3-calcite (CaCO3) makes up limestone-Oxides-metal plus oxygen-hematite-Halides (Salts)-ionic bonds with Cl-Halite -element class-minerals composed of one element-gold copper sulfur-sulfates-minerals with SO4-gypsum, anhydrite-sulfides-metal plus sulfur-pyrite

Are these minerals?-coal formed from compaction and hardening of variously altered plan remains-amber fossilized tree sap, not a mineral-obsidian volcanic glass, lava cools rapidly and not enough time to form mineral structure-not a mineral

Mineral Stability-minerals form and are most happy at particular temperatures and pressures-think about water -crystallize from fluids when conditions are right-high temps melt-solid state when conditions are right

Feldspars-most abundant mineral in earths crust-three main kinds-K (orthoclase)-potassium feldspar-Na (albite)-sodium feldspar -Ca (anorthite)-calcium feldspar

Rocks

-What is a rock?-aggregate of minerals or mineraloids-3 types-igneous-seditmentary-metamorphic

Igneous rocks-born from melts-form deep within the earth at high temperatures-magma molten rock beneath the surface-magma rises since it is less dense than surrounding rock-lava molten rock erupted onto the surface-two main types of igneous rocks-intrusive cools slowly beneath the surface of the earth-extrusive cools quickly on surface of the earth-intrusive igneous rocks - magma cools within the earth-pluton large body of cooled magma-sills skinny horizontal sheet of magma-dikes skinny sheet of magma, not horizontal-sills and dikes like sheets that go through weakness in rocks-extrusive rocks-lava molten rock extruded onto surface-aa (lava) very crusty, not smooth, rough, more viscous-pahoehoe fluid, ropey texture, smoother -can have both types of lava flows in same flow-pillow lava when lava cools underwater-blobs, kind of looks like pillows-flood basalts eruptions that coat large stretches of land with basalt lava-tuff loose volcanic debris welded together to form a rock-Mt. st Helens-cooling rate determines texture-cools fast glassy/lacks internal organized structure-obsidian-cools slowly more organized internal structure, bigger interlocking crystals -granite-chemistry determines the minerals-mafic magnesium and iron-olivine, pyroxene-intermediate has mg and fe but not enough to be mafic-amphibole and mica-felsic feldspar and silica-quartz and feldspar-same chemical composition different cooling rates-basalt extrusive, mafic-gabbro intrusive mafic -andesite extrusive intermediate-diorite intrusive, intermediate-rhyolite extrusive, felsic-granite intrusive felsic-magma cools as it rises and crystals form-minerals form as they reach their happy zone-temperature and pressure-fractional crystallization-as minerals form (elements are removed), chemistry of magma changes-minerals crystalize from cooling magma in particular order-know bowens reaction series

Sedimentary Rocks-made of disaggregated bits of other rock-form at earths surface-underwater counts-weathering produces sediment-piecs of igneous, metamorphic, and even other sedimentary rocks-sedimentary structures-evidence they formed at the surface-i.e. ripple marks-types of sedimentary rocks clastic, chemical-clastic made of actual little pieces of other rocks-defined by grain size-gravel conglomerate-sand sandstone-silt siltstone-clay shale-chemical made from chemicals that came from the disintegration of rocks-precipitate from fluids (ocean, lakes, etc)-carbonates-evaporites (gypsum, etc)-dry lake beds

Metamorphic rocks-heat and pressure cause pre existing rocks to change-formed deep within earth, not melted occurs in solid state-bread analogy-dough represents protolith (original rock)-oven represents heat and pressure-bake bread = metamorphic rock-textures of metamorphic rocks foliated/non-foliated-foliated-preferential alignment of minerals -formed under differential stress (pressure)-slate, schist, gneiss-non-foliated-no preferential alignment of minerals-marble metamorphosed limestone, quartzite metamorphosed sandstone, alabaster metamorphosed gypsum -migatites mixed rocks-in between metamorphic and igneous-evidence for metamorphism and partial melting

Statigraphy and Cross Cutting Relationships

Nicolaus Steno-major founder of statigraphy-found superposition, original horizontality, lateral continuity

-superposition oldest layer at bottom, younger layers above-original horizontality sedimentary rocks form horizontal layers -inclined sed rocks suffered subsequent disturbance-lateral continuity sedimentary rocks are laterally continuous-to certain extent (not forever)

Cross Cutting Relationships-Hutton-something that cuts across or affects another must be younger than material that's being affected-rock that was cut is older than rock cutting across-faults, folds, igneous intrusions

-faults -strike slip transform-normal hanging wall below footwall-reverse/thrust hanging wall above footwall-folds bent, rocks had to be there before being folded-anticline older rock at top, looks like n-syncline younger rock at top, looks like u-intrusions molten nature of igneous rock allows it to burn its way through stones

Unconformities-missing time in rock record-rocks formed episodically, not continuously-gaps called unconformities-nonconformity-disconformity-angular unconformity

-nonconformity erosional contact between igneous or metamorphic units below and sediments above-implications uplift of igneous/metamorphic rock followed by deposition of sedimentary rock-tectonic time scales

-disconformity missing time between two sedimentary units-implications erosion or non-deposition took place across the unconformity

-angular unconformity displays angular discordance across unconformity-implication deposition of unit 1-uplift/tilting/erosion of unit 1-deposition of unit 2-grand canyon has it all

How do we tell if there is an unconformity?-angular look for the angle between sed rocks angular not parallel-nonconformity between seds and igneous/metamorphic rocks-disconformity need marker that will tell us age of the sed rocks-fossil succession

Robert Hooke-fossils might be useful for correlating rocks from place to place-roman coins were used to date successive human historial events-fossils could be used same way-largely ignored

Cuvier-demonstrated extinction occurred -showed past elephants werent same as modern elephants

William Smith-rock types change from place to place-succession of fossils was the same

Fossil Succession summary-no two species are exactly alike-species become extinct and never reappear-like coins-thus fossils can be diagnostic of certain age-index fossils-widespread-short-lived

How geologists display geologic info-geologic map-two dimensional plan view-statigraphic columns and cross sections-two dimensional vertical view

Formation-a formation is a mappable unit of rock usually distinctive from other units of rock and regional in extent-formations can be composed of members-formations can be grouped together to form groups

Geologic time

Organization of time scale-time vs rock units-time is continuous abstract-rocks are not continuous-riddled with unconformities-tangible-thus a distinction is made between t ime units and time-rock units

Geologic time scale is a hierarchy-eon, era, period, epoch, age-geologic time scale is a relative time scale-the time scale was constructed using basic geologic principles, not dates-superposition, lateral continuity, original horizontality, fossil succession, cross-cutting relationships-base of a geologi time unit is usually defined by first occurrence of fossil or groups of fossils

Absolute time vs relative time-relative time-sequence of events, without dates-chronostratigraphic-absolute time-sequence of events with dates-radiometric age dating-chronometric

Fossils vs Radioactivity-most igneous and metamorphic rocks can be dated radiometrically-few sedimentary rocks can be dated-grain probably not formed when rocks formed-but this is where fossils are found (can be dated)

Whole time scale-precambrian 87% of earths history-precambrian subdivided using chronometric means-archean and Proterozoic eons-pahnerozoic eon subdivided using chronostratigraphic means-fossil succession

Geologic rates-gradualism, catastrophism-gradualism hutton, lyell-a cyclic view, rock units formed by continuous rock cycle-no vestige of beginning, no prospect of end-rock cycle-suggested eart was old-dominated many areas of science for 100 yrs-no directional component in earth history-a kind of steady state-caused lyell to doubt darwins theory of evolution since it implied a directional component-catastrophism - cuvier-rock units caused by series of catastrophic events-long periods of stasis with short periods of upheaval-lake Missoula/scablands catastrophes do occur-peak discharge is estimated at 20 time flow of amazon-more than total discharge of all rivers in the world-300 meters deep, 100 km/hr-1000 ft deep w/ force of fire hose

actualism-elements of gradualism and catastrophism are correct-uniformity in process, but not rate-inviolable laws of nature have operated since beginning of time-geological processes are governed by these laws-combination of hutton/lyell, Darwin, and cuviers viewpoints

Rates of geologic events-most are so slow they are nearly imperceptible and take millions of years to show effects-some events are instantaneous

Plate Tectonics

Fossil distribution-fossils can appear in sed rocks-same animal and plant fossils found in different continents-can fit all the continents back together into one-similar fossils on different continents were close together when continents put together

First theory continental drift-idea that continents move horizontally over earths surface-wegener-major problem no mechanism, how could continents move?

New Data to address old ideas-ocean floor bathymetry-crustal densities-continental-oceanic-first map of ocean bottom created by heezen and tharp, mid ocean ridge went all around the world

Ocean Bathymmetry-mid ocean ridges-underwater mountain ranges-avg depth 2500m-trenches-deepest parts of the ocean-deepest over 11000m-abyssal plains-vast flat areas in between ridges and tenchres

Crust: two kinds-continental crust higher than ocean crust since it is less dense-felsic-2.67 g/cm3 -ocean crust-mafic-3.0 g/cm3 (more iron so more dense)

Second theory Plate tectonics-harry hess-american ship captain during war/Princeton professor after-record of seafloor as he sailed around pacific-plate tectonics harrys idea-ocean crust must be created and destroyed -sedimentary cover too thin for 4Gaof accumulation-created at ridges, destroyed at trenches-continens are passive riders on conveyor belt

New Data to address old ideas-geomagnetics-geodynamo produces magnetic field-field behavior used to trace tectonics-distribution of earthquakes-shallow vs deep used to trace tectonics-hot spot volcanism

geomagnetics-geodynamo produces magnetic field-paleomagnetism-magnetic minerals in volcanic rocks record earths magnetic field as they cool -600 C curie point for rocks-like little compasses-magnetic field flips polarity from time to time-magnetic nort becomes magnetic south and vice versa-on average, every 200,000 yrs-not periodic-key observations from paleomagnetism-paleomag at mid ocean ridges shows new crust created at ridges-symmetric magnetic pattern about ridge crest

-distribution of earthquakes-shallow mostly associated with midocean ridges-intermediate/deep are mostly associated with trenches-benioff zones-plotted earthquakes and found deep earthquakes werent randomly distributed-deep earthquakes occurred at trenches-crust pushed down into mantle at trench benioff zones-volcanos can be created at benioff zones due to magma rising as crust being subducted, creates felsic magma-key observations-shallow earthquakes associated with mid ocean ridges-deep earthquakes are only associated with trenches

Hot spots-some volcanoes not near trenches Hawaii-hot spots are fixed, plates move over them-hot spot tracks reveal plate motions-emperor Hawaiian seamount chain for example

plate tectonics unifying theory-outer portion of earth is broken into plates-lithosphere the crust plus upper mantle-plates are portions of lithosphere that behave as a unit-has strength-asthenosphere underlies lithosphere-behaves plastically-less strength-lith plates float along asthenosphere-strength terms not chemical-new oceanic crust is created at mid ocean ridges-magma wells up to fill the crack as plates diverge-plates are recycled at trenches where they dive deep into the earth-continents ride along with the plates-they do not drift around, they are carried around-hotspot volcanoes reveal plate motions-plate tectonics-divergent margin plates come apart-leads to passive margin in contrast with active margin-transform margin plates slide past-convergent margins plates smash together-ocean-ocean, ocean continent, continent-continent-mechanism-this pattern is consistent with convection in the mantle-interior of the earth is much hotter than surface, allowing for convection-newly subducted crust more dense so sinks, then rises as its melted