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Exam 2.docx

7 Pages

Earth Sciences
Course Code
Earth Sciences 2240F/G
Neil Macrae

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1. Cyclonic Storms: (read) The most common cyclonic storm we in southern Ontario experience is a thunderstorm, and only rarely do we experience „the big guys‟: hurricanes (True, we had a small side- effect from Sandy in October, but it wasn’t much to worry about). a. However, on a different scale of course, some ingredients are the same for both. For example, atmospheric fronts are important in both. i. Define „front‟. [2] Fronts are the Boundary between two air masses of different temperatures. ii. Will a warm front or a cold front lift air more abruptly/quickly? [1] Cold fronts lift air the most abruptly. iii. Which type of air is more likely to rise along a storm front: dry air or moist air? Why? [2] Moist Air. The Moist air fuels the storm. (comeback maybe) b. Hurricanes: i. Define „hurricanes‟. [2] - Severe cyclonic tropical storm in the North Atlantic Basin - Originates within the belt of tropical trade winds, rotates counter clockwise around an “eye” with minimum wind speeds of 119km/h. ii. By what parameters do we measure the intensity of a hurricane? [2] Using the Saffir-Simpson Hurricane Scale; the velocity of wind, the height to which the sea rises and the extent of destruction are used to scale hurricanes. Range from category 1-5. iii. List all the conditions essential for successful development of a hurricane north of the equator and in the Atlantic Ocean. [6] - Begin with a disturbance in the westward-flowing air not far from the equator. - The sea surface temperature must be 26°c, this is necessary to produce the latent heat energy needed to power the hurricane. - Needs open water to maintain and grow in strength as it receives its power from warm waters. - Requires a slowly moving or stationary cold front that produces a bulge in the boundary between cool and warm air moving in opposite directions. - Must obtain a wind speed of 119km/h at least to be categorized as a hurricane. 2. Use of Oxygen Isotopes to Tell Past Climate: (read) a. Two oxygen isotopes have proven very useful in tracking climate of the past. i. Name the isotopes. [1] 1O and O18 ii. Note the rough relative abundance of each. 16 [1] 18 O = 99.8% and O=0.2% iii. Is each a stable isotope? [1] YES. 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). i. List what these useful characteristics are, and explain why they are useful in determining temperature. [4] The bond between atoms with a higher mass are stronger then ones with lower masses. As a result O evaporates less readily then O. 16 This is called Fractionation. So with equilibrium between oxygen isotopes and the mineral, temperature can be determined if we can measure the oxygen isotope ratios of mineral phases grown at the time. ii. Briefly describe how the 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 sample has already been age dated ). [Obviously, any temperature determination is going to involve some laboratory work, so work that into your answ]r. [8] COM BACK IF TIME 3. The Uplift Weathering Hypothesis: (read) 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? [1] CO 2 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! [8] Essentially as rocks come under the effects of weathering, specifically rocks containing (Ca) calcium the carbonic acidity of the rain breaks down the rock and joins the calcium and carbon dioxide. This removes the carbon dioxide from the atmosphere; as the result of this process is consumed by organisms (marine). In the case of the Hypothesis the process is rapidly increased and intensified when it is undergone on high plateaus or mountains which usually see fresher rock face (earthquakes) and water-laden clouds that are forced upslope where heavy precipitation occurs. c. Is the growth of abundant vegetation ( on the continents, obviou) a positive or a negative feedback to the Uplift Weathering Hypothesis? Explain. [2] POSITIVE. Pulls CO from the air and adds it to the soil, promoting 2 formation of carbonic acid and the roots breakup the rocks providing more surface for reaction. d. If there is a thermostat control for this hypothesis, define it. [2] As increasing CO2 is pulled from the atmosphere the climate will cool to the point that the factors for weathering will slow and so too will weathering itself; no matter how much fresh rock surfaces are available. 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] It does for the past 100 million years. The only case that it does not cover is one 430million years ago when the Sahara experienced a period of glaciation for around 1 million years. 4. The BLAG Hypothesis: a. Define the hypothesis and describe the mechanism. [6] Most CO co2es from volcanoes. During times of rapid ocean-floor spreading volcanoes are more active so high atmospheric CO and d2ring times of slow ocean-floor spreading there is lower atmospheric CO . 2 Rocks at spreading centers can be dated so we can figure out spreading rates by dating and measuring distances of rock bands from the central spreading. b. If there is a „thermostat‟ control for this hypothesis, describe it. [4] There is, chemical weathering. Essentially as rocks come under the effects of weathering, specifically rocks containing (Ca) calcium the carbonic acidity of the rain breaks down the rock and joins the calcium and carbon dioxide. This removes the carbon dioxide from the atmosphere; as the result of this process is consumed by organisms (marine). c. How can the effectiveness of the BLAG hypothesis be evaluated (i.e. what would you check)? [3] I would check the general distance between rock samples and the spreading center and then tie them to a time frame. After that, provided the rocks are datable, you could then use correlation between date and distance to determine if it was a time of rapid ocean-floor spreading or slow. Thus determining if it was a period of high or low atmospheric CO . 2 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] Yes. It can be used to examine the conditions for any time 100 million years or younger. If can be applied to older testable rocks, but this is generally more rare as mo
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