EARTH 125 1st EditionExam 2 Study Guide: Lectures 9-16Lecture 9What role does time play in Darwin’s concept of Natural Selection and Descent with Modification?There are two types of aging: relative and absolute aging. Relative aging is knowing the order of events but not the corresponding year, month, day, etc. Absolute aging is knowing the exact date. To calculate time elapsed, we can use the following: Time = (present day state) – (initial state)/rateHowever, this assumes the rate hasn’t changed.Regarding natural selection, its effects can be studied over a short time span, yet these effects are relatively negligible. Darwin claimed these small changes (gene frequencies, beak sizes in finches, color in population of moths, etc.) lead to extremely large effects over time. He follows Lyellian uniformitarianism, where actualism = constancy rate + constancy of state, so, Darwin can get big effects only if there’s a lot of time available.Who is Kelvin and what are his methods? How does his age of earth affect Darwin?Lord Kelvin dismissed geological approaches and used a Thermodynamic explanation forthe earth’s age. He claimed the earth’s interior is hot and heat is flowing out; the geothermal heat flow demonstrates that heat is coming from the earth’s interior and not the sun. His Second Law of Thermodynamics claimed that heat flows from warmer to colder bodies.An analogy for this second law is the following: if two loaves of bread started in a 350 F oven, when I touch loaf A, it is 250 F, while loaf B is 100 F. Which one has been out of the oven longer? Naturally, we understand loaf B has been out of the oven longer because it’s colder.His second law of thermodynamics also assumes that in its earliest stages, earth was completely molten. Kelvin concludes that the age of earth is anywhere from 10 million to 100 million years old. Thus, the absolute age of earth is too short to support Darwin’s natural selection and descent with modification. However, upon further analysis, Kelvin’s estimates were inaccurate because he assumed all the heat in the earth comes at the initial time of earth accretion.What is radioactivity and how does it fit into time scales?It’s associated with a release of energy. It negates Kelvin’s estimates of the age of the earth, but also provides a tool for obtaining absolute ages from analyzing rocks. Radioisotopes decay and are naturally spontaneous. They produce energy and convert one isotope into another. In this way, we can figure out absolute aging much more accurately than other ways.Lecture 10What is the Continental Drift Hypothesis?Alfred Wegener hypothesized the existence of a single super-continent: Pangaea, 200 million years ago. Evidence for this are glacial striations – “scratches” on rock surface made by rocks carred by glacial ice. These tell the direction of ice movement and flow. Originally, it was difficult to conceive of continents moving. But, the earth’s surface has 2distinct elevations (continents and ocean floors). They had to understand isostasy: where the height of the object above water level depends upon the relative density of the object compared with the water, as well as the thickness of the object. Similarly, the earth’s surface is “floating” on material that behaves visco-elastically – the surface can move up and down. Continents had to plough through the ocean floor, like ships through water, but there’s no physical mechanism that could explain this. The hypothesis was rejected until the 1960s because there lacked a physical mechanism for moving gigantic pieces of crust across a globe.What do ocean floors have to do with the age of the earth and heat flow? Ocean floors have a lot of topographic variability: ridges, trenches, and islands. They alsoturn out to be much younger than the age of the continents and change in a very characteristic way, with the youngest near the center of ocean ridges, and getting older as we move further away from ridges. The heat that comes out of the ocean floors is not uniform, because the ocean floors arehot at the ridges and cool away from the ridges.Lecture 11What are plate tectonics?There are three types of plate boundaries. Divergent plate boundaries are where the plates move horizontally opposite ways (away from one another). Convergent plate boundaries are when plates move towards each other and go above/underneath one another. Transform Plate boundaries move opposite ways, but not necessarily directly away from another. Plate tectonics are the earth’s crust – a series of rigid plates embedded in a rigid lithosphere, which is “floating” on a highly viscous, fluid layer (asthenosphere). Ocean floors represent the top of a “conveyor belt,” emerging at ridges and diving back into the interior at trenches. Continents ride passively on this “conveyor belt,” may accrete by collision with other continents, and may split by the formation of new divergent margins.Lecture 12What is the evolutionary importance of plate tectonics?The movement of plate tectonics can create barriers in evolution, as well as create continental collisions to extinction. When two continents that had been separated for millions of years collide, these collisions bring together fauna that have been separated for years. What is the first emergence of life on earth? What is life?Life is a self-replicating chemical system, requires energy to remain stable (metabolism), and has cells and a chemical composition. There are various forms of life. Prokaryotes – bacteria and archaea – have DNA not in the nucleus, no organelles, are exclusively unicellular, have asexual reproduction, and are small, with only an external wall. Eukaryotes have DNA in the nucleus, organelles, are uni- and multi-cellular, have mostly sexual reproduction, tend to be large, and have internal scaffolding. These organisms act as chemical factories. Primary producers (“autotrophs,” e.g. plants) take up material from environment (inorganic material), and use the energy of light to convert itto a sugar. The first indirect evidence was found through several ways. First, they found carbon signatures in rocks – the “fingerprint” of life. They also found sedimentary structures of biogenicorigin – stromatolite formation. In the Achaean period, prokaryotes were the life that existed. These bacteria were the first organisms on the planet and the only organisms until 2 billion years ago. They’re