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Published byDorothy Pinch Modified over 10 years ago
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A. Direct Evidence B. Indirect Evidence
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Visible evidence that organisms have changed over time Ex. – Fossils
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▪ Paleontologists are scientists who collect and study fossils. ▪ The fossil record provides incomplete information about the history of life. ▪ Over 99% of all species that have lived on Earth have become extinct. ▪ Where are all these fossils??
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Fossil Formation Water carries small rock particles to lakes and seas. Fossil Formation
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Dead organisms are buried by layers of sediment, which forms new rock.
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The preserved remains may be later discovered and studied.
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Lucy Lucy Coal Formation Coal Formation The following picture is of plant fossils found in coal from the Minto area that are 300 million years old…..older than dinosaures!
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Relative Dating ▪ In relative dating, the age of a fossil is determined by comparing its placement with that of fossils in other layers of rock. ▪ Rock layers form in order by age—the oldest on the bottom, with more recent layers on top. ▪ Grand Canyon Grand Canyon
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Relative dating allows paleontologists to estimate a fossil's age compared with that of other fossils.
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▪ Radioactive dating ▪ Some elements are radioactive and steadily break down into nonradioactive elements. ▪ Radioactive dating is the use of half-lives to determine the age of a sample. ▪ A half-life is the length of time required for half of the radioactive atoms in a sample to decay.
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C-14 breaks down into N-14 at a fixed rate. The half life of C-14 is 5,760 years. When an organism dies, the C-14 in the organism starts to change into N-14. Knowing the half-life, you can compare the amount of C-14 to N-14 to determine the age of the fossil
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Let’s say the fossil we are dating shows 50% C-14 and 50% N-14……. The fossil should be 5,760 years old. If another 5,760 years passed, what would be the ratio of C-14 to N-14? Right!!.........C-14 25% to N-14 75% Potassium 40 is an isotope with a half-life of 1.2 billion years!!
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Evidence we can look at today that suggests we may have a common ancestry with other organisms. 1. Embryological Similarities
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2. Comparative Morphology Homologous Structures (Similar structure but different function!)
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3. Similarities in Biochemistry DNA similarities (98% of our DNA is the same as a chimpanzee) Protein in all organisms is composed of the same 20 amino acids!!
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Direct Evidence – something we can look at that takes us back in time. Ex. Fossils Indirect Evidence – something we can look at that show some kind of evolutionary connection between organisms. Ex. Embryological similarities, Homologous structures, Biochemistry similarities
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Darwin’s explanation of evolution is called Natural Selection. What does the term Artificial Selection mean? Discuss this with a neighbour. Samuri Crab Samuri Crab
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Organisms don’t change to survive, they survive (or die!) because they change!
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