~The Dinosaurs Came In December!~
Background
What is time? For most students, the concept of time is very abstract and leads to difficulties in understanding the Earth's history. Unraveling time and the earth's history are arguably geology's most important contributions to humanity. However, it is difficult for people to appreciate time beyond that of one or two generations, much less hundreds, thousands, millions and billions of years. The following activities can be used to introduce students to the vastness of geologic time and to help them better appreciate the concept of scale.
Objective
Students will construct a time line based on events in geologic history.
Activity
Have students brainstorm in groups to generate a list of events that are part of the Earth's past. Students will draw on their experiences to name topics such as dinosaurs, Pangaea, trilobites, and cave dwellers. Groups can share their events with the rest of the class to prevent counter-productive research. You might want to add a few events to help some of the groups that are having trouble brainstorming. Next step is to have all of the groups spend time in the library or on the internet doing research. Ask them to find the time in geologic history when their events made its mark. Later they will use this information to place the event on the calendar and on the geologic time line. Students choose their own method for displaying the collected data. Cartoons, cave etchings, posters, poems, stories, reports, collages, and bulletin boards are among endless possibilities for creativity and for integrating other disciplines and skills.
Calculations
After checking the accuracy of their historical information, students have to calculate where to place their events or subjects on a year-long calendar. Have the students make their own calendar using butcher paper. Use calculators and the following conversion formula to find the analogous calendar date.
A sample problem may follow this sequence: The first birds appeared 150 million years ago. The age of the Earth is estimated at 4.6 billion years. Mathematically, these two numbers can be compared to a year of 365 days as follows:
Students will find that Days = 11.9. Rounding this off to 12 days, students then subtract 12 days from the end of the year, December 31, which represents the present in this sequence. Thus, on this calendar, the first birds appeared December 19. Students will recognize that this event occurred, relatively speaking, in the not-so-distant geologic past.
The Classroom Calendar
After each student has used the equation to determine the equivalent days that represent the elapsed geologic time for each event chosen, construct a large class calendar including events from all of the groups. Make the daily calendar squares large enough for students to record their results. Display the calendar in a central location, within easy view of all students. Another option is to have one calendar for all of the classes. Make the daily squares in each month large enough so that all of the classes can record their data. With the class display calendar waiting to be filled with information, students can share their research creations with the class. After each student finishes his or her presentation, the class guesses when the event occurred as represented by the year-long calendar. (Each day represents about 12.6 million years.) The groups finish their presentation by adding their data to the calendar. Geologic time takes on a new perspective as students record their information on the appropriate daily squares.
Constructing A Geologic Time Line
Students can construct a combination of the calendar and the time line to link both perspectives. To do this, students need to establish a length that represents the passage of one day on this time line. To find this figure, divide 4,600 (the time line's length in mm) by 365 (days per year). The result is 12.6. A calendar day, then, would be 12.6mm long on the time line. To figure out how many mm to allot to a particular month, multiply 12.6 by the numbers of days in that month.
| Some Important Dates (Subject to Revision!) In The History Of The Earth |
|
| Millions of Years Ago | Event in Geologic History |
| 4600 | Origin of the Earth |
| 3900 | Oldest Dated Crustal Rocks |
| 3800 | Oldest Evidence for Life |
| 2000 | First Oxygen Atmosphere/Ozone Layer Forms |
| 900 | Oldest Metazoan Fossils |
| 510 | Oldest Fossil Fish |
| 458 | First Land Plants |
| 440 | Bedrock in Oxford/Forms/Ohio near the equator |
| 375 | Amphibians Evolve |
| 245 | Huge Mass Extinction at End of Permian Period/Close of the Paleozoic Era |
| 200 | First Mammals |
| 160 | First Birds |
| 145 | Atlantic Ocean First Opens |
| 130 | Angiosperms (Flowering Plants) Appear |
| 65 | Adaptive Radiation of Mammals/Dinosaurs Go Extinct/Close of the Mesozoic Era/Beginning of the Cenozoic Era |
| 3.4 | New Discoveries (Lucy)-Australopithecus Afarensis fossils from Ethiopia - Males And Females Show Sexual Dimorphism |
| 2 | Pleistocene Ice Age Begins/Light From The Andromeda Galaxy Seen Today Left Andromeda 2 x 106 years ago! |
| .600 | Age Of Homo Erectus Fossils From Ethiopia |
| .125 | Oldest Rocks In The Bahamas |
| .100 | Homo Sapiens Appears In The Fossil Record |
| .015 | Last Ice Sheet Retreats From Ohio |
| .007 | Grahams Harbor, San Salvador, Bahamas Floods Due To Rising Sea Level After Ice Sheets Are Reduced To Modern Day Volume |
| .000503 | Columbus Lands In New World |
| Your Birthday |
Enrichment Activities
Extend the time line into the future to show scientific predictions for such events as the burn-out of the sun or depletion of natural resources. Also, students can creatively illustrate or write about their own "future" time lines. This activity builds reasoning skills because the students are forced to base their predictions on information that is presently available. By doing research and collaborating with classmates, students learn about geologic time and processes and gain a perspective not only of the Earth's past, but also of their own.
Links
Source: Earth At Hand, NSTA 1993. Arnold D. Lindaman and Mark McCarthy, North Scott Community School District, Eldridge, Iowa. Geologic Time Scale Project, Journal of Geological Education, 9:9-11, 1991. S.D. Ritger and R.H. Cummins, Interdisciplinary Studies and Geology, Miami University. Adapted by: A. Miles and S. Vance, Rice Model Science Laboratory, Houston, TX.
