geo 102 - exam 1
Does the rate of sediment deposition have to be consistent from location to location?
no
What are the three physical properties that describe a mineral?
1 plane of cleavage - irregular 2 planes of cleavage 3 planes of cleavage - cubic
Completely understand the decay chart discussed in class. An example of a test question is as follows: C14 decays to N14 and has a half-life of 5,730 yrs. If 75% of N14 is left in the sample, how many years have passed? How many half-lives have passed?
11460 years 2 half lives
What is Nicholas Steno known for?
3 principles of stratigraphy (original horizontality, superposition, lateral continuity)
What is a cyclothem? If you were looking at a rock outcrop that had a cyclothem of sandstone, limestone, and shale (listed oldest to youngest) what might this represent?
A vertical rock unit consisting of a series of rock beds that represent changes in the environment Increasing sea level, transgressive, caused by a hot house
What types of things can be dated using C14?
Anything organic
What does the term "Before Present" mean?
Before 1950 i. 1950 is when atmospheric carbon began to be measured
What is the best and worst types of rocks to date? Explain how this relates to the assumptions of isotopic dating?
Best - extrusive igneous (all of crystals are same age because they solidify at the same time) Worst - sedimentary (individual grains so you do not know time of lithification, dating original material not resulting rock after lithification process) also metamorphic (dating restarts clock when application of heat and pressure, date will be metamorphic rock not age of protoliths)
What characteristics are used to ID a mineral?
Color, streak, luster, hardness, cleavage, reaction to acid, magnetism
Before the Huttonian revolution, What events stimulated discussion about fossils?
Disagreement about age of earth, fossils being dated to an age that does not agree with the age that we thought the earth was prior to this time period (not needed for this exam)
Why were Al Wegners index fossils so important in determining that landmasses were once together?
Fossil record showed that fossils of certain species were spread throughout different continents that if the continents were together it would connect the continents together
what is a paradigm shift?
Fundamental change in scientific approach ex. we used to think that the earth was only 6000 year old but now we know it is much older, change from catastrophic to non-catastrophic point of view
What is James Hutton known for?
Huttonian revolution (the present is the key to the past), uniformity of causes, events occur at uniform rate, earth changes to achieve balance
How is a sedimentary rock different than an igneous rock?
Igneous - formed from the cooling of magma (extrusive or intrusive) Sedimentary - formed by the lithification and cementation of metamorphic and igneous, or shells or fossils rocks due to weathering and erosion (bioclastic, clastic, or evaporite)
Why are many fossils not considered to be index fossils? Why did Al Wegener choose the index fossils that he did to develop his ideas on Continental Drift? What was special about these plants and reptiles?
Many do not fit characteristics (found in a larger range of time) Existed on multiple continents to help prove continental drift, found in areas where they would not normal exist as the plates are now
What does "14" represent in C14?
Mass (protons + neutrons)
How are metamorphic rocks formed? What is a parent (protolith) rock? What are the factors controlling metamorphism? What is the length of time it takes for a metamorphic rock to form? How is this time length different than a sedimentary rock?
Metamorphic rocks are formed by metamorphism (heat and pressure, foliated vs non-foliated) Protolith(parent) undergoes metamorphism to form a metamorphic rock Metamorphisms takes tens of millions of years compared to a million years for sedimentary rocks
what are the properties of a mineral?
Naturally occurring, crystalline(a substance that is solid with a repeating 3-D orderly pattern), specific chemical composition(elements bond to form minerals)
Why was the idea of Continental Drift not revisited until the 1960's?
No way to prove how it was happening, idea of convection currents did not come up until 1960's Energy to solve academic problems diverted from 1910-1960 because of world wars and rebuilding after world wars
Characteristics of an index fossil.
Recognizable, widespread area, small amount of geologic time (lysosaurus, mososaurus used by Wegener)
Understand how to calculate and apply concepts of recurrence interval and probability.
Recurrence interval - used to estimate the risk of an event to occur, RI= (n+1)/m i. N - number of years of data ii. M - magnitude of event (largest event on record: m=1, descending order as events get smaller) Probability - used to estimate the percentage of an event to occur each year P% = (1/RI)*100
How long was the Precambrian?
Represents 80% of all geologic time 4.6by - 570 my
How is a rock different than a mineral?
Rocks are made up of minerals, minerals are formed of elements
How is an isotope defined?
Same number of neutrons, different number of protons
What environments do sandstone, limestone, shale, and coal represent? What type of rocks are these?
Sandstone - beach, sedimentary Limestone - shallow marine, sedimentary Shale - deep marine, sedimentary Coal - wetland, sedimentary
Why isn't C14 dating used for rocks?
Short half-life, no carbon left because older than 50,00 years old (because it decays exponentially)
What is the difference between silicate and non-silicate minerals? What mineral is the purest of all silicates? What is an example of a non-silicate mineral?
Silicate - SiO2, the root of majority of minerals on the planet (>70%), quartz is the purest of all silicates Non-silicate - standalone element that forms an element, ex. gold, silver, iron, sulfur
What is a half-life?
Time required to 50% of the atoms of a radioactive isotope to decay to its products
What is Walther's Law used for?
Used to determine the depositional environment of a sedimentary rock, and determine sea level change (worldwide sea level curve using record about regressive and transgressive boundaries around the world)
What were the lines of evidence used by Alfred Wegener to develop his ideas of Continental Drift? Be specific.
a. Index fossils, map in which the continents fit together well like puzzle pieces, glacial deposits b. Problem is that he did not produce mechanism to say how or why the plates were moved
Why is the isotopic decay of uranium used to date the age of the earth?
complete decay occurs over 4.6 billion years
Geologic Time- how are geologic eras, periods, and epochs divided?
era - separated by periods of mass extinction period - defined by distinct changes in the uprising of life epoch - broken up because of climate change
Why can't Radiometric Dating be used to date the age of the earth?
error increases as age increases and the half life of carbon is not old enough
What are the two main differences between an igneous rock formed extrusively and intrusively?
extrusively - cools quickly, aphanitic texture (small grain size) intrusively - cools slowly, phaneritic texture (large grain size)
What is the difference between a gap and a boundary?
gap - missing interval in geologic time boundary - overcoming need for more advanced technology
Why is igneous texture so important for determining the history of igneous rocks?
helps to know the time of cooling which can tel us whether the magma originated intrusively or extrusively
Rock Cycle- Understand components of the rock cycle and how they interrelate (see diagram). What are the three major types of rocks? What do rocks originate from? How can rocks become altered during the rock cycle?
igneous, sedimentary, metamorphic
What is Pangea? What continents make up Laurasia and Gondwanaland?
pangea - super continent laurasia - northern most super continent; north america, eurasia gondwanaland - southern most super continent; south america, australia, africa, antartica, india
What is the # of protons within Carbon? # Neutrons? What is its atomic weight? Be able to solve these questions for any element on the periodic table of elements.
protons- 6 neutrons- 6 atomic weight- 12
What is the main difference between relative and absolute time?
relative time - used when assigning approximate ages absolute time - physical counting methods
what is uniformantarinism?
the present is the key to the past
Define transgressive and regressive facies. Draw these diagrams. What process is likely to cause a regressive facies?
transgressive - ocean approaching on land; high stand, glacial melt, hot house regressive - ocean moving away from land; low stand cold house, glacial freeze
What are examples of physical counting methods?
tree rings, glacial deposits, bi-annual lake sedimentation deposits
What is the uranium disequilibrium series?
used to determine the age of the earth