BIOL 112 1st Edition Lecture 3 Outline of Last Lecture I Categories of Scientific Models II Levels of Scientific Models III Paradigms IV Value Judgments V Bad Theories Outline of Current Lecture VI The Scientific Method VII Evolution A Observations Significant to Evolution VIII Fossils IX Macroevolution of Horses X How Old are Fossils A Relative Dating B Absolute Dating XI Dating Math A Calculating Age XII Carbon Dating XIII Geological Dating XIV Dating Observations Current Lecture I The Scientific Method These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute Two major aspects Observations Facts what we see Interpretations Theories what it means A good theory does two things Explains what happens shows how things work Predicts what will happen if certain conditions are established Not fortune telling or predicting the future but expected data from specified situations experiments II Evolution Evolution a change in population of organisms over a long period of time Basis of change change in genetic composition of population Genetic changes produce Change in biochemistry Change in morphology Change in behavior Any other aspects of organisms under genetic control A Observations Significant to Evolution Fossil Record Anatomical Homologies current organisms Vestigial Organs organs that deteriorate after lack of use Embryological Development Molecular Sequence Homologies genome III Fossils From the Greek dug up Preserved parts of plants or animals that were once alive Hard parts have highest chance of being preserved bones teeth wood shells Taphonomy the science of the decay of organisms over time and how this relates to fossilization Soft parts found less frequently skin feathers leaves flowers rarely even cell structures are found Organic materials usually replaced by inorganic materials stone You can determine the colors and physical characteristics based on the fossils Fossils can help us to determine animal behavior also IV Macroevolution of Horses Shows general trends over the past 60 million years Increasing body size change in proportions Shift of toe structure from many digits to one digit toes to hoof Change in diet dentition from soft leaves brush to hard grasses Example of macroevolutionary sequence Repeated branching speciation events Adaptive Radiations followed by selective survival and extinctions V How Old are Fossils Two dating methodologies A Relative Dating distinguishes older from younger using stratigraphy Index fossils used as markers to recreate a whole history of strata from different locations in one sequence Assembled strata sequence is called the geological time scale We need to apply dates to time scale using absolute dating B Absolute Dating gives an age estimate in years usually by using radioactive decay methodology Radioactive isotopes of various elements will decay internal nuclear event rearrangement in atom Individual atoms decay as random events but probability of decay is predictable for a mass sample of the radioactive form Rates of decay can t be influenced by ambient physical or chemical environments treatments VI Dating Math We can estimate how much Carbon is originally present in a sample and we can measure the amount present now We can also determine how old the same is from the time that the carbon has been present which means when the living thing died and started releasing Carbon A Calculating Age Half life is unaffected by normal ambient conditions temperature pressure chemicals etc In one half life half of the original sample of radioactive material will have decayed In two half lives 3 4 of the original sample will have decayed etc VII Carbon Dating Good only for organic materials and for a few thousands of years maximum practical date is about 60 000 years New wood has 14Carbon content of 15 3 dam older wood would be proportionally less We assume that the rate of 14Carbon production is constant This assumption has been tested and is not completely accurate The rate of 14Carbon production was lower in the past and has increased over the past 30 000 years 14Carbon dates have now been calibrated against wood samples of known age by growth ring counts for example bristlecone pines Pines longaeva now corrected out to 30 000 40 000 years VIII Geological Dating Useful for fossil strata and good for up to a few billion years Usually done in crystals from igneous rocks i e lava flows layered among fossil bearing strata provides absolute data reference ages along the relative stratigraphy series Fossils can be dated using a combination of relative and absolute systems IX Dating Observations Age of the Universe around 12 x 109 years Oldest Rocks age of Earth 4 6 x 109 years Earliest fossils bacteria like 3 5 x 109 years Evidence of aerobic photosynthesis 2 2 x 109 years Earliest eukaryotic fossils 2 1 x 109 years Multicellular organisms 1 5 x 109 years Animal fossils become common Cambrian Explosion 5 5 x 107