The earth's axis of rotation wobbles like a spinning top. There are two periods (a wobble within a wobble): 19,000 AND 23,000 years. Precession has a profound effect on the earth's climate.
It is 10:46:26 AM on Thursday, April 27, 2017. This page has served 182237 visitors and was last updated on Wednesday, May 7, 2014.
Portions of the following exercise are from the article: Ritger, S.D. and R.H. Cummins. 1991. Using student-created metaphors to comprehend geologic time. Journal of Geological Education. 9:9-11.
We use this exercise to introduce students to the vastness of geologic time and to hope they better appreciate the concept of scale. Most students are amazed and shocked by this exercise. Students create a metaphor that is presented to the class. They also compose an essay on why they chose the metaphor they did & they discuss the impact this project had on their thinking. We use this exercise in our Natural Systems course: Patterns & Processes in Natural Systems and in Geology 499/599: Tropical Marine Ecology.
We've all done it. Careful lectures are given on the historical development of a time scale, first with qualitative techniques and then "time stamped" using quantitative methods. We also have students memorize the time scale as part of an earnest effort to facillitate students' appreciation of geologic time. Yet, sometimes despite our best intentions, we fall short. Unravelling time and the earth's biologic history are arguably geology's most important contributions to humanity. Yet, it is very difficult for humans to appreciate time beyond that of one or two generations, much less hundreds, thousands, millions and billions of years. Perhaps we can only hope that students catch glimpses of our rich geologic heritage, particularly when most of our teaching is done in a classroom and not in a field setting. While we feel it is very important for students to memorize the major components of the time scale, we take things one step further by having them create their own metaphors for geologic time. We have found that this exercise begins to make time more "three dimensional" and most importantly, students gain a better appreciation for geologic time and our earth's history. When students are then brought into the field, they "see" more mystery in the rocks. This always makes field trips more fun!
To better understand the concept of geologic time, your next lab exercise is to produce a time-scale metaphor that is true to scale and reflects some of the important events in the history of the earth (see list below). The exercise requires that you produce a metaphor to share with the class and that you write an essay that: (1) discusses why you chose the metaphor you used; (2) shows your math calculations; and (3) discusses what you learned from this exercise including your perspective of where humans fit in the grand scheme of things. Have fun! Be creative! No metaphor is too silly, as long as your math is correct and your choice has meaning to you. Your insructors, however, appreciate unusual and distinctive efforts--creativity is rewarded. Any examples used in class, however, are off limits. Due: Week of 11/6-11/10
Some Important Dates (subject to revison!) in the History of the Earth:
|Millions of Years Ago||Event|
|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||That important first step: Amphibians Evolve|
|245||Huge Mass Extinction at End of Permian Period/
Close of the Paleozoic Era
|145||Atlantic Ocean first opens|
|130||Angiosperms (Flowering Plants) on the Scene|
|65||Adaptive Radiation of Mammals/Dinosaurs Go Extinct/
Close of the Mesozoic Era/Beginning of the Cenozoic Era
|3.4||New discoveries of (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|
|EON||ERA||PERIOD||EPOCH||DATES||AGE of||Interesting Biological Events:|
|Paleocene||58-66||Extinction of dinosaurs|
|Paleozoic||Permian||245-286||Amphibians||End of trilobites|
|Mississippian||320-360||Large primitive trees|
|Silurian||408-438||First land plant fossils|
|Cambrian||505-570||1st shells, trilobites dominant|
|Proterozoic||Also known as Precambrian||570-2,500||1st Multicelled organisms|
|Archean||2,500-3,800||1st one-celled organisms|
|Hadean||3,800-4,600||Approx age of oldest rocks 3,800|
Taken from: MODERN PHYSICAL GEOLOGY, Graham R. Thompson Ph.D., Jonathan Turk Ph.D., Saunders College Publishing and the University of Alaska, Department of Geology.
All You'd Ever Want to Know About Hurricanes and Tropical Weather!
WEATHER & EARTH SCIENCE RESOURCES
OTHER ACADEMIC COURSES, STUDENT RESEARCH, OTHER STUFF
TEACHING TOOLS & OTHER STUFF
Any mail, comments or suggestions? You can Add to my Guestbook ,View the Guestbook or e-mail me privately at HaysC@miamioh.edu.
Thanks for stopping by!
Copyright © 1996-Infinity R. Hays Cummins; All rights