Topic/Unit - Geologic Time Geologic Time Composed by: Lee Falkena Adapted By: Braden Conrad-Hiebner & Cherie Haury-Artz Grade Level* - 4-8 *(can be adapted for younger grades) Iowa Science Standards 2- ESS-1 - Use information from several sources to provide evidence that Earth events can occur quickly or slowly. 4-ESS1-1. Identify evidence from patterns in rock formations and fossils in rock layers to support an explanation for changes in a landscape over time. MS-ESS1-4. Construct a scientific explanation based on evidence from rock strata for how the geologic time scale is used to organize Earth s 4.6-billion-year-old history Introduction This unit is a pre-activity for students to complete before visiting the Delving Deep: Scientific Discoveries from Iowa s Ancient Sea! exhibit in the University of Iowa Mobile Museum. Geologic time, or the history of the earth, occurs over millions of years, and to express this idea to learners is no easy task. One of the best ways to help the student's understand is through visual learning, or seeing how large the gap of time is between when the earth was created and when life first began. How do scientists know that this is true? Through relative and radiometric age dating. Relative dating is taking the concepts that one knows about stratigraphy and applying that to the layers of rock that they may see. Relative age dating also uses fossil evidence to place the rock layers in order according to when the fossils live and comparing that RELATIVE to other fossils both above and below the rock layers. About the exhibit: Researchers from the Iowa Geological Survey at the University of Iowa discovered evidence that a meteorite struck the earth near what is now the town of Decorah in Winneshiek County, Iowa. This event took place during the Ordovician Period, 465 million years ago. The meteorite created a crater in the earth s crust estimated to have been 3.5 miles in diameter and several hundred meters deep. The crater was flooded by a tropical seaway, creating the unusual environment that allowed
for the spectacular preservation of marine fossils. In some cases, even soft bodies or tissues were preserved. These fossils provide important new information about the creatures which inhabited this ancient tropical sea and their living environment. Instructional Objectives 1. Students will investigate the age of the earth and its selected points of natural and biological historical development through the analogy of a clock (in 24 hours to the very second). 2. Students will measure the time and history of the earth on a roll of calculator tape 4.56 meters long and create a conversion chart for billions and millions of years into meters and centimeters. 3. Students will create their own geologic time chart based on the specific list of dates and events given. 4. Students will investigate the ideas of relative age dating using jumbled letters and fossils coupled with the ideas of stratigraphic concepts to recreate two stratigraphic columns using relative age dating. Major Concepts Understand: Expanse of geologic time (both visually and mentally), vastness of the gap between earth's formation and the start of life (and how long humans have been around compared to how long the earth has been formed), ideas of relative age dating using sequencing of letters and fossils, extinction Apply: Concepts of stratigraphic placement (Principle of Original Horizontality, law of Superposition), relative age dating with letters and fossils, extinction Materials & Equipment Calculator or adding machine tape, scissors, meter ruler, pencils or colored markers Geologic time scale poster and worksheets (attached) Instructional Activities Engagement Activity (20 min)
To get students to start thinking about the breadth of geologic time, a short demonstration can be done displaying geologic time relative to a clock. The following analogy can be made: Midnight (4.5 billion years ago) - earth forms from cosmic dust 3:20 A.M. (3.96 billion years ago) - age of oldest rock ever found 9:23 P.M. (500 million years ago) - first animals with backbones 11:00 P.M. (190 million years ago) - age of the dinosaurs 11:35 P.M. (80 million years ago) - Rocky Mountains start to form 11:58 P.M. (6 million years ago) - small stream begins carving Grand Canyon 11:59 P.M. and 26 sec. (1.8 million years ago) - earliest humans appear 11 :59 P.M. and 45 sec. (750 thousand years ago) - humans begin using fire 11:59-P.M. and 59 sec. (10 thousand years ago) - last Ice Age ends Exploration Activity #1 (1 Class period) In order to further emphasize the idea of geologic time, a visual aide can be employed after that short discussion. This visual aid will require the students to measure 5.5 meters of calculator tape and measure and mark off events in the earth's history. The students are first asked to, using a meter stick, measure 5.5 meters worth of calculator tape for each small group. Be sure that each group member has a specific role in this project and each member may have a group of ages to measure out and mark (5 min.) Using the handout ("Some Important Events in Earth's History") providing relative dates and events, the groups should divide these dates and events into equal parts for each student. They should then use the meter stick to measure these dates and mark them off using a scale of 10 cm = 1 million years. They should label the event (preferably in pen or sharpie), and color them in (optional) (20 min.) The students should begin to visually see the large span of time where nothing (biologically speaking) was taking place in earth's early history. They should then notice how biological activity has only occurred in a recent, relatively short period of time. Particularly humans! Discussion questions (15 min.) - Begin in the same small groups as before, where the students can discuss the answers in a small group and then contribute later to a larger class discussion:
Conversion questions: How many years is 100 centimeters? How many centimeters is 2 million years? How do we know all of this information on geologic time? Where does it come from? How can we tell the age of each layer? How do you know that one layer is older or younger that the other? Give examples in your explanation. How does extinction factor into determining whether fossils are relatively older or younger than each other? Safety Guidelines The only safety concerns for this group activity would be the use of scissors and meter sticks. Students could be injured if they are horsing around with these items. Consideration of Students with Special Needs Support may be needed for students with physical disabilities during the times of measuring and cutting. For those with psychological impairments who may not fully understand the concepts being displayed, the group activities, particularly the cutting and measuring activities, can be a great way to learn more social behavior disciplines rather than scientific concepts. Assessment Plan Assessment should be made during discussion sections. At the end, the teacher may observe whether students understood the concepts by collecting their papers with their predictions, observations, and final conclusions. Assessment can also be made by viewing their geologic time scales constructed from calculator tapes and checking for accuracy.
Some Important Events in Earth s History Cambrian Explosion of life forms - 535 million years ago First animals with backbones - 500 million years ago Large meteorite strikes near present-day Decorah, Iowa - 465 million years ago First amphibians - 375 million years Earliest reptiles - 320 million years ago First major mass extinction event - 252.5 million years ago First Dinosaurs - 230 million years ago First mammals appear - 200 million years ago First flowering plants - 130 million years ago First birds - 160 million years ago Extinction of the dinosaurs - 65.5 million years ago Second major mass extinction event 65.5 million years ago First primates - 60-55 million years ago First human ancestors (Hominins) - 13 to 7 million years ago A small stream starts carving the Grand Canyon - 6 million years ago Humans begin to use fire - 750,000 years ago Last Ice Age ends - 10,000 years ago Native Americans enter the New World - 20,000 years ago Humans enter Iowa - 13,000 years ago Christopher Columbus discovers the New World - 525 years ago