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Homework Questions PG 287 Q. 1: The chances of one individual being born with a beneficial mutation is very low. How then is it possible for mutations to play such a key role in evolution? ANSWER: Evolution acts on such large time scales that even though the chance of a beneficial mutation is rare, there is enough time for many to occur and proliferate. Homework Questions • PG. 287 Q3: Explain why harmful mutations do not accumulate over time and cause harm to populations. ANSWER: Harmful mutations cause harm to the individual and evolution will select against individuals with harmful mutations. These individuals will not breed with others, causing the harmful mutation to disappear from the population. Homework Questions • PG. 287 Q9: How do the genetic diversity of a population and mutation rates limit the ability of breeders to create organisms with desired traits? ANSWER: Hint: Think of the blue rose. Breeders can only work with the genetic diversity that is already present in the organisms population. If a trait does not exist in an organisms genome, a breeder cannot just create that mutation. Mutations are random and rare. This means that beneficial mutations are unlikely to happen. Homework Questions • PG. 319 Q28: What is artifical selection, and why is it called artificial? ANSWER: Artificial selection is directed breeding in which individuals that exhibit a particular trait are chosen as parents of the next generation. It’s called artificial because it is controlled by human choice, not by nature. Evidence for Evolution I: The Geological Record How old is the Earth? Creationism: 5 000 – 10 000 years Science: 4.54 billion years How do we know? Creationism: 5 000 – 10 000 years - various religious texts Science: 4.54 billion years - geology, paleontology Scientific Methods for Dating the Earth: Absolute Dating Absolute Dating - determining a specific age of an object or event Absolute Dating: Radiometric Dating • Radioisotope - an atom with an unstable nucleus capable of undergoing decay • Radioactive atoms give off particles over time and change into another isotope Example: Carbon-14 decays to Nitrogen-14 Radiometric Dating • This decay occurs in a predictable way • The amount of time it takes for 50% of these isotopes to decay is called its Half-Life • After one half-life, 1/2 the C-14 isotopes remain • After two half-lifes, ¼ (half of ½) remains Radiometric Dating • After two half-lifes, ¼ (half of ½) remains • After three half-lifes, how much C-14 remains? – 1/8 remains (half of ¼) Half-Life • Carbon-14 is often used to age younger fossils: it has a half-life of 5730 years (can age fossils as old as ~60 000 years) • Organisms take in C-14 throughout their life and when they die they cannot take in anymore • Then the total amount of C-14 begins to decay predictably Carbon-14 undergoes decay to form Nitrogen-14. By comparing the amount of Carbon-14 to Nitrogen-14, we can determine the age of a fossil using the half-life. Half-Life • Carbon-14 has a half-life of 5730 years • Therefore after 5730 years, an object will have ½ the C-14 isotopes it once did – How many years would it take for an object to have ¼ the C-14 isotopes it once did? – What about 1/8? C-14 Half-Life After two half lives, ¼ remains After three halflives, 1/8 remains Radiometric Evidence • Other examples of radiometric dating: – potassium-argon: 700 million year half life – uranium-lead: 1.3 billion year half life • The oldest rock on Earth is dated to 4.4 billion years • Some solar system meteorites have been dated to 4.5 billion years Labradorite • Rock found in Labrador, Newfoundland • Incredibly old! • 1.29 – 1.35 billion years old! Is Age Significant? • Of course it is! • Evolution is a process that occurs over hundreds of thousands or millions of years • Radiometric dating suggests our planet is not just millions, but billions of years old Scientific Methods for Dating the Earth: Relative Dating Relative Dating – the science of determining events relative to each other Relative Dating • The method that was used before we could use radioisotopes to date materials • Some materials don’t have radioactive isotopes so we must use relative dating • Still useful today especially when used with absolute dating Relative Dating Absolute Dating Evidence for Evolution: The Fossil Record Fossil – ancient remains, impressions, or traces of an organism that have been preserved in rocks or other mineral deposits Fossil Formation • Fossils only form in specific conditions • Oxygen must be absent, to prevent the body from being decomposed by microorganisms • Hard shells and bones are more likely to be preserved than soft-bodies organisms • Organisms may be preserved whole in amber Theory of Plate Tectonics • The scientific theory that describes largescale movements and features of Earth’s crust • The Earth’s crust is made of plates • These plates move around • Move very slowly Fossils and Plate Tectonics • Fossils of the same species have been found in Africa, India, and Antarctica, but nowhere else on earth • Plate tectonic theory explains this – How? Pangaea Fossils and Plate Tectonics • Plate tectonic theory explains this – How? • Species would have lived together where all three continents connected at some point in history Fossils: Significance to Evolution? • Fossils give us a snapshot of early species • They help us understand where new variations have arisen • They suggest transitions between species The Fossil Record - Fossilized species often resemble modern species The Fossil Record • Despite similarities to modern species, most fossilized species are extinct today • Example: – Carcharodon megalodon Great White shark The Megalodon The Fossil Record • Sometimes, if we are lucky, fossil lineages can be very detailed • We can see many steps in the evolution of a species Example: Whale Evolution Questions • Textbook • Page 313 #2, 3a • Page 320 # 31, 32, 33abc