Geologic Time on a Strip of Paper Introduction The Earth is 4,600,000,000 years old. That s 4.6 billion years! But what does this mean? This activity is designed to help you get a feel for the age of the Earth and how it has changed through time. The activity is to make a time line representing the history of the Earth. The time line will be a straight line on a strip of "adding machine paper." The paper will be 5.0 meters long. The beginning of the time line will represent the formation of the Earth 4.6 billion years ago and the end will represent the present. Step I. Making a Length We will want to divide the age of the Earth into 100 equal parts, which we will indicate by hash marks on our time line (see Step II). Dividing 4.6 billion years by 100 equals 46 million years. So each hash mark will represent 46 million years. Dividing 4.6 meters by 100 equals 4.6 cm. So each hash mark will be 4.6 cm long. Your measuring tool to make your time line will be a strip of paper or wire 4.6 cm (note: centimeters) long. You will need to make one out of a scrap of paper of a piece of wire or something else. We will refer to your piece of paper or wire as a "length." Step II. 100 Hash Marks A. Find a piece of floor to call your own that is about 5 m long. Bring along a pencil, and your length. Use books or shoes or some other such object to hold the two ends of your paper to the ground. If you end up working on carpet, grab a clipboard to slide under your paper so you always have a hard surface to write on. B. About 20 cm from one end begin drawing a straight line down the middle of your strip. The line should be 4.6 m long. That leaves 20 cm or so blank at each end. C. At each end write your name. Also write your name on the back of each end. D. Draw a hash mark across the width of the paper at the beginning. This hash mark will represent the origin of the Earth 4.6 billion years ago. E. Lay down your length at the beginning hash mark along the center line. At its end draw a small hash mark, say about 2 cm long across the center line. Do this again and again until you have made 100 hash marks. Every tenth hash mark should be about twice as big and the regular ones, say about 4 cm across the center line. Label every tenth hash mark, 10, 20, 30,. The final hash mark should go across the width of the paper. The final hash mark represents the present. Geologic Timeline on a Strip of Paper, 4/1/12, Page 1
Step III. Geologic Time Divisions Now we are going to add some meaningful details to our timeline. At the beginning of the time line, add the following details: E A R T H F O R M S 4,600,000,000 years ago 0.0 4.6 billion Now, go up to hash mark 17. A little less than half way between hash mark 17 and hash mark 18 add the following details: E A R L I E S T L I F E 3,800,000,000 years ago 17.4 3.8 billion Now, in-between these two divisions, and the details about what happened during the time between 4.6 and 3.8 billion years ago. This time division is called the Hadean. Write this word in large print, in a bold color, between the two boundaries. On the next page you will see some of the important things that happened during the Hadean: Solar system forms, Sun begins to emit light, Earth begins to take shape, core forms, oceans and atmosphere develop, oldest known rocks, earliest life (bacteria) appears near the end. These things happened, in order, from the beginning of the Hadean until the end. Write them underneath the center line, in smaller print, from the beginning of the Hadean until the end. Use the next page as reference and add all of the details at the correct place on your timeline. Your timeline will be more attractive and easy to read if you use colored pencils to add details. NOTE: Make sure you understand the difference between the events that define a boundary in the geologic timeline and events that occurred during an interval. Ask for help if you do not understand this! Geologic Timeline on a Strip of Paper, 4/1/12, Page 2
Years ago Comment Lengths 4,600,000,000 Earth forms 0.0 4.6 billion HADEAN Solar system forms, Sun begins to emit light, Earth begins to take shape, core forms, oceans and atmosphere develop, oldest known rocks, earliest life (bacteria) appears near the end. 3,800,000,000 Earliest life 17.4 3.8 billion ARCHEAN Bacteria begin photosynthesis, early continents form, plate tectonic begins, oldest fossils, first eukaryotes (life more complicated than bacteria), bacteria come onto land 2,500,000,000 Life is producing oxygen in ocean 45.7 2.5 billion PROTEROZOIC Oxygen atmosphere forms, oldest eukaryote fossil, algae, soft-bodied animals, protective ozone layer 543,000,000 Explosion of diversity of life 88.6 543 million PALEOZOIC Gondwana forms, arthropods, hard shelled animals, chordates, fish, land plants, Pangaea. Dominant life includes: ferns, invertebrates, fish 248,000,000 Mass extinction eliminates 94.6 248 million most life on Earth MESOZOIC Pangaea breaks up, earliest reptiles, dinosaurs, conifers, seed plants, birds, mammals. Dominant life includes: conifers, reptiles, dinosaurs 65,000,000 Another mass extinction 98.6 65 million CENOZOIC Continents approach present day arrangement, dominant life includes: flowering plants, insects, birds, mammals 0 Present 100.0 Geologic Timeline on a Strip of Paper, 4/1/12, Page 3
Optional, Advanced Work Part I: The Cenozoic Notice that the Cenozoic, the last 65 million years of Earth history, is all included in the last 1.4 lengths. That s since the dinosaurs went extinct. Since each length is about 4.6 cm, that works out to about 6.5 cm. Add the following to your timeline. Since it is all at the end, you may need to be creative in how you do his. Years ago Comment cm from the end 45,000,000 Oldest rocks in Cascade Mountains 4.5 45 million 25,000,000 Portland, which has been under the 2.5 25 million ocean water, finally becomes dry land 5,000,000 Earliest human-like creatures evolve 0.50 5 million 1,600,000 Beginning of Pleistocene ice age 0.16 1.6 million 10,000 Oldest documented writing 0.001 10 thousand Note: A coarse human hair is about 0.01 cm in thickness. On this time scale the oldest documented writing is about 1/10 the thickness of a human hair, a distance too small to see with the unaided eye. Geologic Timeline on a Strip of Paper, 4/1/12, Page 4
II. Time scales and the rates of naturally occurring events For each of the following think of naturally occurring events (that is events that have nothing to do with humans). And think of events that have a clear beginning and a clear end. Answer each one on your own paper. A. Think of a naturally occurring event that happens on a time scale of less than one second. B. Think of a naturally occurring event that happens on a time scale of a few seconds to a minute. C. Think of a naturally occurring event that happens on a time scale of a few minutes to an hour. D. Think of a naturally occurring event that happens on a time scale of a few hours to a day. E. Think of a naturally occurring event that happens on a time scale of a few days to a month. F. Think of a naturally occurring event that happens on a time scale of a few months to a year. G. Think of a naturally occurring event that happens on a time scale of a few years to a decade. H. Think of a naturally occurring event that happens on a time scale of a few decades to a hundred years. I. Think of a naturally occurring event that happens on a time scale of hundreds to thousands of years. J. Think of a naturally occurring event that happens on a time scale of thousands to hundreds of thousands of years. K. Think of a naturally occurring event that happens on a time scale of hundreds of thousands to millions of years. L. Think of a naturally occurring event that happens on a time scale of many millions to billions of years. Geologic Timeline on a Strip of Paper, 4/1/12, Page 5
III. Calculations Perform the calculations necessary to determine how many lengths correspond to the indicated boundaries in Earth history. Show your work. Geologic Timeline on a Strip of Paper, 4/1/12, Page 6