ES 10 Geologic Principles; Test 1; October 25, 1994; Alfred Hochstaedter Relax ---- Everything little thing is going to be alright. 1. a) (4 pts) Besides the atmosphere, what are the things that make Earth different from the other terrestrial planets (Mercury, Venus, Mars); i.e., why is Earth the ŌSpecial PlanetĶ? 1) Bioshpere 2) Hydrosphere 3) wheathering and regolith b) (4 pts) Now for the atmosphere; what are the things that make the EarthÕs atmosphere different from that of the other terrestrial planets? Less CO2 More O2 (More N2 as well) c) (4pts ) What is the definition of the Gaia Hypothesis? The Gaia Hypothesis: The physical and chemical condition of the surface of the Earth, of the atmosphere, and of the oceans has been and is actively made comfortable by the presenece of life itself. This is in contrast to the conventional wisdom which held that life adapted to the planetary conditions as it and they evolved their seperate ways. d) (4 pts) How do the various things you listed in part a) interact with each other to regulate the average temperature of the Earth. Plants (Bioshere) take CO2 from the atmosphere and contribute O2 to the atmosphere. Lack of CO2 in atmosphere lowers temperature -- less greenhouse effect -- which enables hydrosphere to be liquid. Liquid water (hydrosphere), in turn, is essential for life. O2 in atmosphere enables chemical weathering. Hydrosphere being transported in rivers helps with weathering. Weathering makes soils, which enable some forms of life by providing nutrients. Some CO2 is sequestered in carbonate rocks and other hydrocarbons in the lithosphere, which keeps them away from the atmosphere. This is an interaction involving the biosphere. e) (4 pts)What implications do the Gaia Hypothesis have for the search for extraterrestrial life, especially those proposals that involve manned search parties? Life causes atmosphere to be out of equilibrium. This information about other planets is available from remote spectroscopy on Earth. -- No need for manned space travel looking for extraterrestrial life. f) (no credit; answer only if you have time) What do you think about all this Gaia stuff? What are the strengths and weaknesses? IÕm really interested in what you think. 2. a) (9 pts) Please use labelled diagrams to help explain both compositional and physical layering. Draw and label diagrams. b) (3 pts) What is the difference between the crust and the lithosphere? Crust is a compositional layer; lithosphere is a physical property layer. Crust is part of the lithosphere. c) (4 pts) What is the definition of Uniformitarianism? The same Earth processes operate today that have been operating throughout Earth history. Optional: Processes have stayed the same, although rates are now different. d) (4 pts) What is the evidence for Uniformitarianism on Earth? Things like graded bedding or cross bedding. Evidence comes from comparing present-day environments with older rocks. We can see the same types of structures in both. 3. a) (10 pts) What are the important geologic features observed in this slide (Grand Canyon), and what do they indicate about Earth History in this particular spot? 1) Lower package of sedimentary rocks -- deposition of sediments 2) Angular unconformity -- uplift and deformation of lower package of sed rx; erosion of these uplifted rx to a flat surface; probable lowering to lower levels 3) Upper package of sedimentary rocks -- renewed deposition of sediments; land surface may have lowered to below sea level to accomplish this. 4) Cutting of the Grand Canyon by the Colorado River -- Land must have been uplifted once again so that a second period of erosion could occur. b) (10 pts) Fill in the blanks of this geologic time scale. 4. a) (2 pts) Describe the differences in shape between shield volcanoes and strato-volcanoes (use diagrams if you like). Shield Composite (drawings) b) (4 pts) What kind of eruptions do these two kinds of volcanoes commonly have, and what is the composition of the rocks that commonly come out of these volcanoes? Shield: Relatively gentle eruptions of basalt lava flows that flow easily down the mountain. Composite: Both explosive and lava eruptions of more differentiated rocks like andesite through rhyolite. c) (4pts) What are the controlling factors that influence the kind of eruption and the shape of the volcanoes, and how do they work? In other words, how or why does this controlling factor work? Viscosity and gas content are the controlling factors. Exsolving gas can cause explosive eruptions, but only if the magma is viscous, which prevents the gas bubbles from easily getting out. Viscosity is caused by polymerization of silicate anions. Disolved H2O at convergent margins comes from seawater going down the subduction zone. d) (4 pts) Draw BowenÕs Reaction Series here. e) (6 pts) What is crystal fractionation, and what is it about minerals crystallizing from magmas that makes it work. Use a phase diagram or the mass balance equation (Ctotal=CsolidXsolid+Cliquid Xliquid and Xliquid + Xsolid = 1) as an example to help explain your answer. (Either an example of a phase diagram or the equation will do here; you neednÕt use both.) The main point is to show that minerals crystallizing out of a magma are not the same composition as the original magma. Once these crystals separate from the original magma, the composition of the resulting magma will be different, i.e., differentiated. This can be shown by either changing liquid composition on a phase diagram or using the mass balance equation. 5. a) (5 pts) Start by drawing a picture of a 14C atom, labelling all of the protons, neutrons, and electrons (in their appropriate energy shells; remember that the innermost shell holds only two electrons, while the next one holds a maximum of eight electrons). In the space beside your drawing you define the atomic number (which is 6 for Carbon) and the mass number (or the atomic weight; use whichever one you remember). What is the mass number for 14C? Atomic number = number of protons; Mass number = number of protons + neutrons Mass number for 14C = 14. b) (5 pts) Explain the difference between ionic and covalent bonding in minerals. As an example, draw covalent bonds between a Si atom and four Oxygen atoms to form a silicate anion (Silica has 4 electrons and Oxygen has 6 electrons in their outermost energy shells, which are all you need worry about here). Beside your drawing, explain how you figure out what the charge would be if this complex anion were to later form an ionic bond with some other cations. Covalent bonding is the sharing of an electron; it is a directional bond that needs a specific electron to work. Ionic bonding is an electrostatic force created between two ions of opposite charge. Optional: This electrostatic force can be distributed between several different cations. The charge for the silicate anion is -4; each of the Oxygen atoms has space to gain an additional electron. There are four Oxygens in the silicate anion, thus the charge of -4. c) (5 pts) Using a diagram, explain how Beta decay works to transform 14C to 14N. Be sure to explain the changes (or lack of) in mass number and atomic number during the transformation. A neutron can be thought of as a proton plus an electron. If a neutron undergoes decay, a proton and an electron are produced at the expense of the neutron. The nucleus loses a neutron, but gains a proton, which is balanced by the electron that is also produced during the beta reaction. The mass number stays the same, but the atomic number increases by 1 (because the number of neutrons decrease by 1). d) (5 pts) Turns out he had measured 10 quadrillion 14C atoms in the pumpkin at the beginning of party and knows that there are only 5 quadrillion 14C atoms in the pumpkin now. You volunteer that the half life of 14C is 5700 years. How long have you been at the party? You decide itÕs time to be heading home. 5700 years.