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This exploration of microfossils in drill core data allows students to investigate evolutionary patterns in marine microfossils, and the potential response of these biota to global change, using the CHRONOS online database. Students generate, using a tool on the website, bar graphs of occurrences of taxa belonging to four types of marine microfossils (planktic foraminifera, calcareous nannofossils, diatoms, and radiolarians) through a chosen ten million year time span of the latest Mesozoic and Early Cenozoic eras (between 70 and 30 million years ago). They examine the bar graphs to determine the ages (to the nearest half-million year) of species' first occurrences and/or last occurrences in this worldwide set of data. The students make a list of these ages that may indicate environmental changes, and then organize the gleaned data as a table in a spreadsheet. Students then use the graphing wizard to produce a bar graph depicting the number of originations and extinctions per half-million years, and interpret it. This interpretation includes a discussion of the overall pattern of rates of evolutionary change in marine microfossil species, speculation on causes of changes (both originations/first occurrences and extinctions/last occurrences of species), and observations of trends in the most active timeframes. The students will consider how life may have responded to external and internal forcing of abrupt change, and develop a fundamental understanding of the reasons for the subdivisions of geologic time (i.e., they are based on naturally-occurring events in Earth history). Students also use a resource on the CHRONOS website to examine the morphologies of species that disappeared at a point in time when many species were terminated by a catastrophic event, and compare these morphologies to survivors and species that appeared soon after this event. They speculate about the causes for the changes.
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