Historical Geology Study Guide 1
Historical Geology Study Guide 1 GEOL1005
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This 14 page Study Guide was uploaded by Kate Notetaker on Wednesday February 3, 2016. The Study Guide belongs to GEOL1005 at George Washington University taught by Catherine A. Forster in Winter 2016. Since its upload, it has received 119 views. For similar materials see Historical Geology in Geology at George Washington University.
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Date Created: 02/03/16
Lecture Notes Historical Geology history of physical and biological earth Physical Earth o Certain things are changing Geography – location of everything (oceans, continents, etc.) changes over time Topography – elevation changes (land and sea) Climate – where its hot, where its cold, seasonal changes Atmosphere – Free oxygen, how much CO2, etc. o Look at it in a much larger geological time scale Many changes THROUGH TIME o Entire surface of the Earth is moving North American continent moving about 5 cm a year Slow in our life time but not in the long run History of the biological Earth o How life on Earth has changed Changes in the physical earth can change the biological earth (and vice versa) Configuration of the continents and the water bases were much different in the past Example: Rocks at top of Mt. Everest is a marine limestone o Formed on the floor of a warm, shallow sea o Contains fossils of shelled marine animals o Went from the bottom of the ocean to the top of the tallest mountain in the world Example: Indian subcontinent began a rapid 64,00 km journey north and eventually collided with southern Asia o Once it does that, its northward movement rapidly slows down o When any two deformable objects run into each other it forms a crumple zone o Collision of India and southern Asia formed a mountainous region at the crumple zone Change in geography AND topography o India is still moving north and the Himalayas are rising at a rate of 1 cm per year Eight million years ago the mountains became high enough to trap and divert precipitation to their south and east o Once the Himalayas got high enough the clouds got trapped and so the water got dropped on the Indian subcontinent This is what cause the monsoons (periods of extreme rainfall) Water is trapped on the India side of the rising mountains o Moist air is prevented from reaching Central Asia leading to the formation of great deserts such as the Gobi Started when the monsoons did o Climate changes happened with topography changes Climate change Steady global temperature rising after the industrial revolution with a sharp spike after World War 2 Normal in climate for there to be much variation but it is much warmer today then it was in the past 1000 years We are in post glacial period o We don’t know if there will be another glacial period When you go 65 million years back, it’s a lot warmer o Eocene period is very warm o We’re still in one of the coldest periods in history Time Geological time scale younge st Tenet #1 – Law of Superposition Oldest stuff is at the bottom Youngest is at the top old Era Period Epochs Cenozoic - began 66 Holocene million years ago, ends Pleistocene today Pliocene Miocene Oligocene Eocene Paleocene Mesozoic – began 252 Cretaceous million years ago, Jurassic ended 66 million years Triassic ago Paleozoic – began 541 Permian million years ago, Pennsylvanian ended 252 million Mississippian years ago Devonian Silurian Ordovician Cambrian Proterozoic – began 2500 million, ended 541 million years ago Archean – began 4000 million years ago, ended 2500 million years ago Hadean – began 4.6 billion years ago, ended 4000 million years ago Rocks One or more minerals Each mineral unique chemical formula elements Unique set of physical properties (includes how hard it is, what shape it is, etc.) Most common elements that make rocks (listed from most to least) O, oxygen Si, silicon Al, aluminum Fe, iron Ca, calcium Na, sodium K, potassium Mg, magnesium SiO2 quartz, the most common mineral Minerals Silica tetrahedron Unit cell Basic building block One silicon atom in the center surrounded by three oxygen atoms All the other silicon and oxygen will accrete onto it, does it in a very orderly fashion that is determined by the configuration of the original It takes time to accrete more of these elements onto it as the crystal grows Orderly external arrangement and internal arrangement Internal structure determines external shape Unit cells of all minerals conform to one of seven basic crystal classes Properties specific to each mineral Chemical formula Crystal structure Hardness of the mineral Density Color Cleavage (how the mineral breaks) Melting point Two classes Silicate minerals (contains silica) Quartz Feldspars Micas Clays Non-silicates (important minerals that don’t contain silica) Limestone Evaporites (salts) Ironstones Minerals compelled to form in three different ways (3 conditions) Solidification from a “melt” molten rock Non-random process Crystallization / freezing This is how igneous rocks form Deciding factor for what mineral forms: o Temperature o Availability of elements Wait for the melt to cool down to their melting point Bowen’s Reaction Series High T˚ - 1200˚ Olivine Ca – Feldspars Pryrovenes Ca …… Na Amphiboles Ca – Na feldspars Biotite mica Na feldspars Potassium feldspars Muscovite mica Low T˚ - 600 ˚ Quartz Never find quartz and olivine together since they form at different temperatures We know which minerals will be associated with each other from this table because of each melting point When the melt is still very, very hot all the elements are floating free As the high temperature minerals are forming they use some of the elements, often the rarer elements o Only the most comment elements will remain in the liquid melt o By the time you get to the low temperature, there will only be certain elements available Precipitation saturated water Main way in which limestone and evaporites are formed (sedimentary rocks) Solid State Diffusion metamorphism Atoms rearrange themselves into new materials without melting Heat + pressure to existing rock recrystallization without melting Metamorphic Rocks Igneous rocks Speed at which melts cool determines the size of the crystals and then the texture of the resulting rocks o They go hand in hand o Coarse texture cooled slowly o Fine texture cooled quickly o Can have the same composition but different textures TEXTURE COARSE FINE High Temp gabbro basalt Mid Temp diorite andesite Low Temp granite rhyolite Sedimentary rocks o Formed from the detritus of older eroded rocks (clays, sand, pebbles, boulders) or precipitated from oversaturated water (carbonate, rock salt, gypsum) o All sedimentary rocks Form at the surface of the earth Form at low temperatures and pressures (unlike igneous and metamorphic rocks) Metamorphic Rocks o Undergo change in both their structure and mineral composition due to the action of heat, pressure or chemical activity o During metamorphism Result: new minerals and textures o Any kind of rock can be metamorphosed o New minerals that form are also linked to temperature ranges If we know the new minerals, we know how much heat was applied to make it o Metamorphic grades How much heat is applied to create the mineral o Metamorphic textures texture depends on pressure Foliation: occurs as a response to pressure Minerals respond to the pressure by aligning themselves perpendicular to the pressure Foliated metamorphic rock o Slate: no grains visible o Schist: fine grains of minerals, lots of micas Non-foliated rocks: just heat, no pressure. Random arrangement of mineral grains Marble: metamorphosed limestone Quartzite: metamorphosed sandstone o Types of minerals tells us about the temperature of its formation o Texture of the rock tells us about the pressure that was applied on the rock Igneous rocks o Temperature determines which minerals crystallize from a melt o If we know which minerals make up the rock, we know its thermal history Three different kinds of rock o Igneous o Sedimentary Clastic Precipitated oversaturated ions o Metamorphic Example: Navajo Sandston (Jurassic) o Nearly pure, rounded quartz sand in enormous desert dune deposits o Cross beds Gives an indication of the wind pattern o Remains of giant dune fields Example: Kayenta Formation o Siltstones and sandstones with occasional thin limestone beds o Lake deposits o Evidence of flowing and standing water Ripples in top view indicating running water Shows a river channel with ripples in side-view Also beds with mud cracks o A lot of fossils including small dinosaurs, turtles, frogs, pterosaurs, and mammals o Navajo Sandstone lies ABOVE the Kayenta Formation Kayenta is older Wind or air isn’t as dense as water, so it can’t move things as well o Bedload Material that is moving by rolling or jumping at the bottom of a channel Coarser o Suspended load The material that is being carried by the water itself Finer material What to know o Timing of events o Order of events – what happened first, what happened last, etc. o Rates at which things happened Relative dating o Determining the order in which events happen o Using the law of superposition Things that can happen to disturb the rocks o Deformation Folding and tilting of the rocks Have to deposit the rocks before you fold them o Igneous intrusions Igneous rock is pushed into the rock already there Dikes – they cut across Sills – go with the strata Ex. Can be like lava flowing across the top o Faults – break in the rock that comes straight through it The two resulting parts can move different ways This can make the rock become displaced Law of Cross-Cutting relationships o Igneous intrusion or a fault is always younger than the rock it cuts across o You can’t cut across rock unless the rock is already there Vertical strata o Have to look very closely to find out which way is up and which way is down Absolute Dating radiometric dating o How to find out the actual numeric age of rocks o Radioactive decay isotopes Isotopes are atoms of the same element but differ in the number of neutrons Atomic mass = number of protons and neutrons Atomic number = number of protons o Tells us which element it is Elements differ in their number of isotopes o Unstable stable isotope Parent daughter Loss of protons or neutrons radioactive decay Change between parent to daughter happens over time Decay begins as soon as the crystal forms o You cannot date sedimentary rocks this way Can date minerals o Radioactive decay happens at a predictable and measurable rate Rate: decay constant When half of the parent has converted to daughter, that is the first half life Half life: 0.693 / o Minerals We can date it by the ratio of the amount of parent and the amount of daughter and its decay constant Equation d T = (1 / ) ln ( p + 1 ) Error is only 1% o Carbon-14 dating Half life of carbon is 5730 years Only used to date organic materials that are less than 80,000 years old Used a 40t in40rchaeology o Example: K Ar Half life is 1.25 billion years o Example: U 235 Pb207 Half life is 704 million years New techniques for dating precipitated rocks o The crystal in limestones often contains Uranium Can date them because they contain enough uranium o A lot of sedimentary rocks have igneous intrusions in them Helpful because you can date those If you know the order of things, you can figure out around how old it is Divergent Boundaries o Plates are pulling away from each other Actually being pushed away from each other by new crust coming up and accreting itself Brand new crust/rock/lithosphere being formed o Spreading centers o Lithosphere the crust and upper mantle Asthenosphere is where the lithosphere starts to melt (partially molten) o Asthenosphere starts to come up and thin out the lithosphere Eventually causing a fraction o When this happens it almost always happens in a triple-junction Splits apart with three different “arms” Each arm forms an elongated valley bounded by faults Two of the arms will succeed and form a spreading center, the other one will fail Continent begins to spread apart through the arms that succeed o New crust is produced at the ridges and accreted to the trailing edge of the plates o Hot spots: mantle upwelling in one place Narrow plume hot material coming up in one hot spot Convergent Boundaries o When two plates are pushing against each other o Continental plate to oceanic plate collision Oceanic plate is thinner The oceanic plate is going to get subducted by the continental plate since it is thinner Trench forms at the subduction form Will run up and down the continental plate Will have a chain of volcanoes parallel to the subduction zone Angle of the subducting plate will determine how far inland the mountain chain will be o Continental to continental collisions Orogeny If compression continues, one will subduct under the other Deformation o Metamorphism o Bend and fold o Faulting This is how plates can be destroyed Sometimes they will come together and movement will stop Foreland basin On other side of thrust belt Down warped area Evolution Charles Darwin o Studied at Cambridge o After he got out of Cambridge Went on the HMS Beagle to South America Studied for 5 years Would send specimen and data he collected back to London o He found that: living organisms are very variable extinct organisms were very closely related to the living organisms he found o Settled down and became a gentleman farmer for the rest of his life Married rich and didn’t have to work o Did a lot of pigeon breeding: Found that he could start with one kind of pigeon and get a new breed o Start with one basic form and through selective breeding you can come up with many different forms o During his voyage he had seen these finches Galapagos island Different kinds of beaks depending on the environment they lived in Each island had different kinds of fauna Birds had different beak shapes to eat what was available Robert Malthus o You have to control human population otherwise you will have too many people to feed o Darwin used Malthus ideas This became the foundation for what we call “survival of the fittest” Transmutation of species o How species change evolution o Natural selection as the mechanism for this transmutation 1858 Darwin got a letter from Alfred Wallace o He almost came up with the same ideas as Darwin about evolution o Darwin and Wallace present a paper on evolution 1859 Darwin publishes his book on the origin of species Darwin saw evolution as descent with modification Gregor Mendel o Bred peas o Mendelian genetics o Found that inheritance followed very strict rules Unchanging, not random o Basic unit of inheritance: genes Figured out how these are passed down from generation to generation Mechanism for evolution to work on o 1865 Mendel publishes his findings Pretty much ignored o 1890 Mendel’s findings were rediscovered and figured out how it all worked (especially with Darwin’s findings) o Genes were all linked together in a chain like strand: DNA Tells the organism what its going to look like, how its going to behave, etc. At first, we did not know what DNA looked like (structure) Because of this we could not know how it reproduced 1952 Rosalind Franklin and her students worked with X-ray diffraction o Photo 51 found that DNA was a double helix 1953 James Watson and Francis Crick published how everything was arranged with this double helix Double Helix of DNA o Linked together through “base pairs” of amino acids o Gave the clue of how DNA replicated Caveats to DNA being passed down o Mutations or “mistakes” happen all the time Natural or by external factors DNA doesn’t stay the same, it changes Some of these mutations are helpful, some are the opposite o Horizontal gene transfer One species to another Study published last year that says there are around 145 foreign genes in the human genome From bacteria, virus, plant material, etc. Hox Genes regulatory genes o Regulate what the other genes do o Tells you where everything is supposed to be (where your eyes/legs/other trait is supposed to be on your body) Species evolve not the family or an individual o Have a Genus name and a Species name For humans, genus is Homo and species is sapiens Genus name is always capitalized, species is not o A lot of species are very variable Variation between a species could be large or small Variation can also be partitioned Vary among segments of species o Change from one species to another is “speciation” Difficult to observe in the world today Can happen quickly, can be slow all depends on the natural pressures Can be effected by geology Ex. Lesser Antilles anole lizards o 3 different groups of lizards o lava flows that separated group 1 and 2 and another that separated two from three o Two of the groups were closely related and the other was less similar o The lava flow between group 2 and 3 was more recent You can look at the order of events to make sense of evolution of species o Geology can drive the variation/evolution of some species Textbook Notes Chapter 1 pg. 13-14 Most of our knowledge about Earth’s interior comes from the study of seismic waves Earthquake always begins at a focus o Focus place within Earth where rocks move against other rocks along a fault Produces seismic waves o Fault surface along which rocks have broken and moved Earth is divided into several discrete concentric layers o Core Earth’s center Solid, spherical inner portion and liquid outer portion consist primarily of iron o Mantle forms a thick envelope around the outer core Complex body of less dense rocky material that constitutes most of Earth’s volume o Crust caps the mantle Consists of still less dense rocky material Mohorovicic discontinuity or Moho o Abrupt increase in velocity o This signals the passage of seismic waves from the rocks of the crust to denser rocks of the mantle o Moho dips downward beneath the continents Mafic igneous rocks that form oceanic crust o Dark colored rocks o Rich in magnesium and iron o Much less common in continental crust than felsic rocks Felsic most common mineral of continental crust o Lighter colored, less dense rocks o Rich in silica and aluminum o Poor in the heavier element iron Ultramafic rocks rocks of the mantle o Even richer in iron than the oceanic crust Continental crust o Not only stands above oceanic crust but also extends farther down into mantle o Extends farther down beneath a mountain range than it does elsewhere Isostatic adjustment upward or downward movement o Keeps the crust in gravitational equilibrium o Floats on the denser mantle o Responsible for the continental crust phenomenon Isostasy o Root beneath a mountain acts to balance the mountain Lithosphere crust and upper mantle firmly attached to each other Asthenosphere below the lithosphere o Known as the “low-velocity zone” of the mantle o Seismic waves slow down as they pass through it o Composed partially of molten rock Chapter 3 pg. 55-57 Life on Earth divided into three domains o Archaea o Bacteria o Eukarya Prokaryotes cells lack certain internal structures, including nucleus to house their genetic material o Includes Archaea and Bacteria o Unicellular Eukarya Contains all other known organisms o Presence of a nucleus and internal membrane bound bodies (organelles) Archaea is more closely related to the Eukarya than it is to Bacteria Each domain further divided into smaller and smaller groupings called clades o Each clade includes a common shared ancestor and all of its descendants Eukarya are divided into at least six major groups groupings of organisms are known as taxonomic groups or taxa o Study of the composition of and relationship between these groups is known as taxonomy Species group of individuals that can interbreed Major Taxonomic Categories (ex. Humans) o Domain: Eukarya o Kingdom: Animalia o Phylum: Chordata o Class: Mammalia o Order: Primates o Suborder: Anthropoidea o Superfamily: Hominoidea o Family: Hominidae o Subfamily: Homininae o Genus: Homo o Species: Homo sapiens Phylogeny of life tree of life, shaped more like a bush with many branches o To be united within a higher taxonomic category: a group of species must not only resemble one another but also form a discrete portion of the tree of life tracing back to a single branching event
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