Exam 2014, Answers - Catastrophic Events Long Answers PDF

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Earth Science – Catastrophic Events Long Answers 1. Cyclonic Storms Fronts Define Front i. the boundary between two air masses of different temperatures. Fronts lift warm moist air. Cold fronts lift air the most abruptly Which type of air is more likely to rise along a storm front: dry air or moist air? Why? ii. Moist air. If the air is moist and unstable, thunderstorms will form along the cold front. iii. Moist Air is less dense than dry cool air and therefore will be lifted quicker Hurricanes Define Hurricanes iv. A severe tropical storm that forms in the North Atlantic Basin. v. Hurricanes originate within the belt of tropical trade winds, roughly from 5 degrees to 20 degrees from the equator. vi. Hurricanes rotate counterclockwise around an “eye” with minimum wind speeds from 119 km/hour What parameters are used to measure hurricane intensity? vii. Saffir- Simpson Hurricane Scale 1. Wind Speed 2. Surface Pressure 3. Storm Surge Describe all the conditions essential for successful development of a hurricane north of the equator and in the Atlantic Ocean viii. Hurricanes need warm tropical oceans that have surface temperatures of 26o or higher ix. Needs low vertical wind shear, especially in the upper level of the atmosphere. Moisture and light winds above them x. Needs high relative humidity values from the surface to the mid levels of the atmosphere xi. Need a tropical wave xii. Needs saturated lapse rate gradient near the center of rotation of the storm. A saturated lapse rate insures latent heat will be released at a maximum rate xiii. Need a disturbance in the westward flowing air not far from the equator

2. Use of Oxygen Isotopes to Tell Past Climate a) Two oxygen isotopes have proven very useful in tracking climate of the past Name the isotope and note their relative abundances i. O16 and O18 ii. O16 forms 99.8 % of all oxygen present, O18 forms the rest. The ratio of the two isotopes is 1/400 b) A slight difference in characteristics between the two oxygen isotopes (named above) allows us to determine temperature from some natural samples (i.e. they provide us with a natural geothermometer). 1. List useful characteristics and explain why they are useful in determining temperature iii. Measuring the oxygen isotope ratios in rock allows for the determination of temperature. iv. The two main isotopes differ in their mass and thus evaporate at different rates. Since oxygen 16 is lighter, its molecular bonds are not as strong and it evaporates more readily. v. Therefore at higher temperatures the ratio of oxygen 16 to oxygen 18 would be lower. vi. Variation in materials containing these isotopes is fractionation and it varies with temp, therefore we can know the temperature by analyzing oxygen isotopes of mineral phases. 2. Briefly describe how th`e oxygen isotope values in a sample of glacier ice from, say, Antarctica can reveal climate data at the time the ice formed (assume the ice has already been dated). vii. You can find the ratio of oxygen 18 to oxygen 16 in the ice sample and use it to determine the temperature for a given time. As mentioned above, the difference in mass numbers of the two isotopes leads to different evaporation rates. viii. By analyzing the relative ratios of O16 to O18 in a sample of glacier ice, we can determine the temperature of the atmosphere when this ice was formed; the level of fractionation would vary with the temperatures of the time. By combining the age of the sample by radioactive dating and the temperature during the samples formation we can determine the temperature at a particular time.

3. Storage Range Effects on Climate:

a) Define three astronomical cycles that Milankovitch recognized, giving their name and period. Diagrams may help! - Eccentricity- Earth’s orbit around the sun varies in a systematic manner over periods lasting 100,000 years. At times Earth’s orbit is highly eccentric and other times it is circular - Tilt of the Axis- The tilt of Earth’s axis changes every 41,000 years from 21.5 to 24.5 degrees. Lower

tilt means less radiation of the sun in the summer and more in the winter for the Northern regions - Precision of the Equinoxes- The wobble of the Earth’s axis is due to the varying gravitational pull of the Sun and the Moon on Earth’s equatorial bulge causes changes in the direction of the Earth’s tilt. This processs called precession occurs every 26,00 0 years. b) Describe two types of geological records which can provide an excellent proxy for these Milankovich cycles, giving us information on past changes in Earth’s climate - icehouse is a glacier and interglacial period supposed to go into glacial and the switch is supposed to happen every 100 thoudand years – relating to Milankovich c) Name and describe in detail at least two other kinds of catastrophic events that can dramatically alter climate on a short (year to 1000s of years) time scale. Several possible answers can be found here! Need Answer

4. Define Greenhouse and Icehouse climate states. Which state is Earth in (or close to) now? a. Greenhouse- times when continental ice sheets are absent. Warmer climates with decreased CO2 content b. Icehouse- times when continental ice sheets are present. Cooler climates with increased CO2 content i. Earth is in/ close to the Icehouse What compound, from out atmosphere, is soluble in water thus making virtually all rain at least slightly acidic? c. CO2 Describe how the activity of rock weathering by this acidic rain can change climate (i.e. describe the specific mechanism of the Uplift Weathering Hypothesis); provide a present day example. d. Acid rain will eventually break down any rock containing calcium and combine that calcium with carbon dioxide to form calcium carbonate, thus reducing the carbon dioxide concentration in the atmosphere and cooling the climate. e. This hypothesis states that the process of chemical weathering will proceed much faster if the rock is broken up (ie by converging plates). It also noted that “fresher” rock surfaces can lead to increased rates of weathering. f. Current day example is India pushing into Asia causing the formation of Himalayas??? (not sure) Throughout late Mesozoic Era seafloor spreading was rapid. Describe and explain the effect that rapid seafloor spreading have had on relative sea level and global temperatures. How might rapid seafloor spreading change global climate? g. During sea floor spreading, mid-ocean ridges form as volcanic rock erupts there (think: MidAtlantic Ridge). The higher the volcanic ridges (i.e. the faster the spreading rate), the smaller the ocean basin, leading to flooding of the continents (i.e. the higher the sea levels).

5. Mass Extinction a) Mass extinctions are rare extinctions that result in total elimination of large amounts of existing species. For an extinction to be classified as a mass extinction it must: (1) be a global event, (2) involve all ecologies (marine and terrestrial), (3) the timing of the event must be short (less than one million years), (4) a large number of species must become extinct (must be >30%) b) Geological Time End Ordovician

Species Extinction Rate 85%

Likely Reasons for Extinction There was a series of sudden, short-lived glaciations, reducing sea levels. Species surviving an early glaciations would move into new niches and be killed by the next event The extinction of 370 mya was likely caused by an impact of a large asteroid due to tsunami evidence and deposits of black shale and Ir. The extinction of 360 mya was likely due to anoxic seas. More terrestrial life meant adding nutrients into marine systems resulting in algal growth and anoxic conditions Could be due to: (1) asteroid impact: direct evidence absent but tektite evidence exists (2) emissions from Siberian traps: would not have been enough (3) ocean flow patterns and anoxia: warmer ocean = less oxygen = anoxic (4) release of methane clathrates due to ocean warming

Late Devonian

370 mya = 50%, 360 mya = 72%

End Permian

96% of all marine and 70% of all terrestrial

End Triassic

55-65%

Pangaea was breaking apart so there was a lot of volcanism, lots of CO2 would have been pushed into the atmosphere and the oceans, and the warming would have resulted in release of methane clathrates, leading to anoxic conditions

End Cretaceous

65-75% (including dinosaurs)

The Chicxulub crater impacted earth with such speed that it would have vapourized the asteroid and the rock it hit sending dust into the atmosphere; rock fragments turned to fireballs and burned Earth’s forests releasing tonnes of sulfur (leading to acid rain) initial freezing period (due to

dust) then warming due to huge release of carbon from rocks 6. Impacts  The kinetic energy of an impacting meteoroid is pretty awesome…! With the equation KE=1/2 mv2 in mind, explain with reasoning which impacting object would make a bigger explosion: a 10000 tonne rocky object arriving over Chelyabinsk, Russia at 25 km/s, or a 4000 tonne comet iceball arriving over Tunguska, Russia at 60 km/s. - The 10000 tonne object moving at a speed of 25 m/s would impact Earth with over 3 million joules of kinetic energy. - The 4000 tonne object moving at 60 m/s would impact Earth with over 7 million joules of kinetic energy. Therefore the 4000 tonne comet would make a bigger explosion as it has more than twice the energy of the 10 000 tonne object. - The main reason for this is that the velocity is squared and thus it is the strongest contributing factor. - Even though the Chelyabinsk object is twice as heavy, it is moving less than half as fast, Meaning its impact will be much less severe than something moving much faster.  Going upscale, the geologically recent Zhamanshin crater in Kazakhstan is a true impact crater 13.5 km in diameter. When did the Zhamanshin event occur and what was the estimated diameter of the impacting object? How often does this size of impact event occur? - The event occurred 1 million years ago and the object was estimated to have a 1km diameter. Objects this size impact roughly once every 1 million years.  Let’s say you are mapping in some non-glaciated barren region of interior North America. The little soil that is present measures only about 1 to 2 m thick, but there are enough areas with no soil that you can see that all the solid rock of the region is layered sedimentary rock. In the center of the region you discover a large circular crater measuring 3.5 km diameter. Obviously, you have to put it on the map, but do you call it a volcanic crater or an asteroid impact crater? By now, you know quite a bit about each process, so answer the following and show your preferred choice: - list the properties you might expect to find in the region if the crater was created by volcanic processes;  1) Volcanic vents present inside the crater  2) Presence of igneous rocks around the crater, rhyolite, andesite, basalt,  3) Nearby hot springs,  4) Presence of a magma chamber below the crater. - list the properties you might expect to find in the region if the crater was created by an asteroid impact.

1) Overturned rim around the edge of the crater, central uplift with an underlying fracture zone at the base.  2) Shatter cones – cone-shaped patterns in the rock that point toward the impact site…created by energy waves emitted at impact.  3) Tektites – Tiny glass spherules created during impact as the rocks are melted and vaporized…raining back to the ground as glass spheres. They will be in the soil surrounding the crater.  4) Traces of iridium, normally uncommon in the earth’s crust, are indicators of extraterrestrial matter. - Which is the ‘winner’ for the feature you found?  Impact Crater, traces of Iridium. 7. The Uplift Weathering Hypothesis: This is the story that relates climate to the atmosphere, rocks and weathering, and is enormously important. 

a. What compound, from our atmosphere, is soluble in water thus making virtually all rain at least slightly acidic? Co2 is a compound from out atmosphwere that is solubcle in water. Greater amount of CO2 gets into the atmosphere from emissions ofrom volcanoes and hot springs. Some smaller amounts come from human activity. Acid rain will eventually break down any rock containing calcium and combine that calcium with carbon dioxide to form calcium carbonate, thus reducing the carbon dioxide concentration in the atmosphere and cooling the climate. [1] b. Describe how the activity of rock weathering by acidic rain can change climate (i.e. describe the mechanism of the Uplift Weathering Hypothesis); you need to be specific – generalities won’t do! 

weathering can proceed much faster because of availability of more surfaces if rocks are fragments to finer grain size.

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The finer the grain, the greater the active area.

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The fresher the rock surface, the more rapid the weathering rate

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Reactions show that even mildly acidic rain containing carbonic acid will break down any rock containing Ca and combine the calcium with CO2 to form calcium carbonate. Carbonic acid in acid rain breaks down silicate rocks that contain Ca to eventually make

calcium carbonate needed by marine organisms. Total CO2 content of the atmosphere is reduced by such reactions This process is effective over a long time scale. Form acid rin, start weathering (slow), get weathered products to oceans, form shells to fix or remove CO2 from the system  process could cool down a climate caused by high CO2 content in the greenhouse procided:

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o Abundance of fresh rock exposed at surface to be weathered o Sufficient precipitation o Abundance of time c. Is the growth of abundant vegetation (on the continents, obviously) a positive or a negative feedback to the Uplift Weathering Hypothesis? Explain. [2] The growth of venegation speeds up the process of Ca forcming with CO3. Mildly acidic rain containing carbonic acid will break down any rock containing Ca and combine the calcium with CO2 to form calcium carbonate. Carbonic acid in acid rain breaks down silicate rocks that contain Ca to eventually make calcium carbonate needed by marine organisms. Total CO2 content of the atmosphere is reduced by such reactions 

Speed up the process if rock is covered with vegetation o Pull CO2 from air, add it to soil – promoting formation of carbonic acid

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Breakup rocks with roots – more surface for reaction

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Would have been a slower rate of chemical weathering if amount of fresh rock available to be weathered were small

d. If there is a thermostat control for this hypothesis, define it. The negative feedback – as more CO2 is pulled from the atmosphere, climate will inevitably cool to the point that factors essential for weathering will slow – weathering slows no matter how much uplift and

fresh rock surfaces are available. Chemical weathering slows down. The – feedback is the decrease temperature Chemical weathering is viewed as an active driver rather than a thermostat –Weathering is not a response – forcing factor. It’s difficult to find a thermostat control for this process. One could hypothesize continued weathering of a rapidly uplifted area reducing the greenhouse effect to nearly zero – and Earth would freeze. e. Over the past 100 million years or so, does the Uplift Weathering Hypothesis successfully describe the Greenhouse-Icehouse climate for all, part or none of that time? [2] Part of the time  after the event of India pushing against Asia – creating Tibetan Plateau – climate cooling began quickly  dropped Earth into an Icehouse by 35 million years ago – we are still in an Icehouse. 8. The BLAG Hypothesis: a. Define the hypothesis and describe the mechanism. [6] - plate tectonics influence global climate by moderating atmospheric CO2 concentrations. - The rate of sea floor spreading control the delivery of CO2 from rocks into the air resulting in long-term climate change - tie plate tectonics to behavior of atm CO2 - most CO2 in the atm comes from volcanoes, during times of rapid-ocean floor spreading – lots of active volcanoes – high atm CO2 (warmer climate) - during times of slow-ocean floor spreading there are fewer V – low atm CO2. We are currently in an Icehouse - rocks at spreading enters can be dated – figure out their spreading rates by dating and measuring distances of rock bands away rom central spreading b. If there is a ‘thermostat’ control for this hypothesis, describe it.

- during any long period of fast tectonic spreading and an abundant supply of CO2 to the GH, things would get pretty hot  chemical weathering is the negative thermostat - thermostat is the rate of weathering because it’s going to control the CO2 in the air produced by volcanoes – trying to lower it

c. How can the effectiveness of the BLAG hypothesis be evaluated (i.e. what would you check)?

- We can test this hypothesis with some confidence only for rocks of spreading centers younger than 100 mya. - 100mya – seafloor spreading was rapid, atm CO2 was high and no ice sheets - BLAG hypothesis is supported by the reliable geological evidence we have (use the table) - Indication of faster spreading rates around 100 mya than at present- supports BLAG hypothesis

- Testing for spreading rates

[3] d. Over the past 100 million years or so, does the BLAG Hypothesis successfully describe the actual Greenhouse-Icehouse climate for all, part or none of the time? [2] - The Blag hypothesis is supported by the reliable geological evidence we have. - We can test this hypothesis with some confidence only for rocks of spreading centers younger than 100 mya. - 100mya – seafloor spreading was rapid, atm CO2 was high and no ice sheets - We are currently in an Icehouse: times when ice sheets are present on continents - Rates >50% higher...