Viewing the Geologic Timeline from the Perspective of Integrated Science by Stephen R. Mattox and Lisa M. Richardson Department of Geology Grand Valley State University Allendale, MI ABSTRACT Construction of a geologic timeline is a common activity in K-8 classrooms and in the training of preservice teachers. The procedure is well described in Teaching about Evolution and the Nature of Science (National Academy Press, 1998). The activity is commonly viewed through the prism of biology with fossil organism displayed across the spectrum of geologic time. We have developed complimentary timelines that emphasize the significant events of and interconnectedness between the atmosphere, solar system, and geosphere. Some key conditions/events/processes we feature include: differentiation of the Earth; formation of the Moon; changes in cratering rates; early, nitrogen-rich atmosphere; volcanism on the Moon; oldest mineral, rock, and fossil; geologic evidence of atmospheric composition; gradual increase but low abundance of oxygen; presence of ozone and abundant oxygen as life emerges onto land; coalescence and dispersal of Columbia, Rodinia, and Pangaea supercontinents and resultant effects on species distribution; impacts; mass extinctions; Ice House and Hot House climates; and high carbon dioxide levels. We will present results assessing if the activity encourages a more holistic view of the Earth history 4.6 Ga 1 st prokaryote cells Columbia supercontinent Oldest fossilsLunar volcanism Stromatolites thrive Banded-iron deposited Oldest mineral Rodina supercontinent Copernicus forms Current glacial Earth forms differentiation Intense bombardment O 2 Gradually increasing Ozone layer forms N 2 -rich atmosphere Pangea supercontinent 1 st eukaryote cells! Fish Land plants Dinosaurs Humans Mammals Tetrapods 2.6 Ga 3.6 Ga 0.6 Ga 1.6 Ga Hard shells Moon forms Stromatolites still thrive No free O 2 in atmosphere Photosynthesis adds O2 to oceans O 2 still being added to oceans All Fe in oceans deposited, O 2 released to atmosphere Dry land is lifeless Extinction INTRODUCTION Grand Valley State University offers an undergraduate degree in Integrated Science to prepare future K-8 teachers. The program requires 12 credits each in biological, physical and Earth/space sciences. Although this framework is well suited to convey the basics of each field, little time is available to highlight the connections between the exosphere, geosphere, hydrosphere and atmosphere, and biosphere across geologic time. Many states require teachers to explain how rocks and fossils are used to determine the age and geologic history of the earth. One method of presenting this information is the construction of a geologic timeline by the students. The procedure is well described in Teaching about Evolution and the Nature of Science (National Academy Press, 1998). Although the timeline commonly shows a biological perspective we believe students will benefit from looking at other important events in the history of the Solar System and placing events in relative order and in context to previous and subsequent changes. To guide students towards a more holistic view we have constructed a new timeline that presents major events in the exosphere, geosphere, hydrosphere, atmosphere, and biosphere using geologic time as the canvas. METHOD Classroom discussion guides the students to mark off a timeline on adding machine tape at a scale of 1 meter equals one billion years (1 cm = 10 million years). We divide the class into four groups that construct four timelines (combined below). Each group receives and envelope with photos/text of events and their time of occurrence. Student tape their timelines on the blackboard and then tape their photos/text at the appropriate time. Events/text are color coded to facility recognition and discussions: exosphere, geosphere, hydrosphere and atmosphere, and biosphere. 1 st Ice House Oceans form RESULTS Some key points to raise with students: ● early differentiation, oceans, atmosphere…life ● accumulation of oxygen in atmosphere ● biological changes following changes in ocean/atmosphere controlled by geosphere/hydrosphere ● plate tectonics influences species distribution ● singular events (differentiation, bombardment) vs. cycles (Ice House, super-continents…extinctions) DISCUSSION Student Comments ● “I always felt there were connections between the different spheres but never really thought about it much until now.” ● “There is a pattern of connectivity between all the areas of science. One sphere couldn’t exist without the preceding events in other spheres occurring.” ● “I’m surprised at how long it took for prokaryotic cells to evolve into organisms; I always assumed prokaryotic cells didn’t come into existence until much later in earth’s history. I also never learned that there was more than one super continent, but am very interested to learn more about the two that formed before Pangaea.” ● “There’s a lot of information introduced all at once, so you can get a few very general ideas before you go into information overload.” ● “Everything about the time scale is surprising to me. 4.6 Billion years is an unimaginable amount of time and scientists’ figuring out what was going on back then is amazing.” ● “I didn’t know that the earth was so old.” Problems ● Students enter the class with little prior knowledge; thus, many of these observations come as revelations. ● There is a large amount of data in a short class period. ● Some events shown as pinpoints in time, not as spans. ● How to assess? ● What did we miss? ● Permission to use photos/diagrams. Possible Solutions ● Fred Mackenzie’s Our Changing Planet An Introduction to Earth System Science has an excellent chapter on “Evolution of Planet Earth” that would make a useful reading assignment. ● Keep the timeline visible in the classroom and refer back to it frequently. ● Train our peers in astronomy, meteorology, and biology to stress connections and to take the long view. In the classroom, students constructed four timelines and then compared events from four perspectives. 2 nd Ice House ●●●● ●●●●●● ●●●● ●● ● ● ● ●● Oldest multicellular fossils O 2 ~10% 3 d Ice House Increments of 100 million years