Lesson 8: The History of Life on Earth Time: approximately 45-60 minutes, depending on length of discussion. Can be broken into 2 shorter lessons Materials: Double timeline (see below) Meter stick (to construct time line) Black marker (to construct time line) Timeline markers (from web site) Tacks, pushpins or tape Text: The History of Life on Earth (from web site 1 for each 1 or 2 students) Text: Lesson 8: History of Life (from web site 1 per group) Overview Students read an article about how life has evolved on Earth over the past 3.8 billion years. They construct a timeline and place different organisms on the timeline at the time of their first known appearance. Students then consider the age of their planet and evaluate how much the life on their planet might have evolved in that time based on what they learned about the evolution of life on Earth. Purpose This lesson introduces the idea of evolution and shows that evolution is not a constant, linear process. For most of Earth s history evolution proceeded very slowly and most life on Earth was (and still is) unicellular and microscopic. It helps students realize that the age of a planet may have a great impact on the nature of any life forms inhabiting it. Standards A complete list of the standards covered by this lesson is included in the Appendix at the end of the lesson. Procedure Prepare materials beforehand: It will take between 40 and 60 minutes to prepare the materials for this lesson. Print the timeline markers from the web site. Separate the individual markers by cutting them along the dotted lines. Make a double timeline. The timeline should be made on a roll of paper such as fax paper or wide calculator paper, which can be bought at most office supply stores. If using a roll of regular calculator paper make two separate timelines and display them one over the other so that both beginning points line up. The upper timeline will mark the time since the formation of the Earth from left to right, going 400 million years into the future at the right. The lower timeline will begin at 4.6 billion years ago at the formation of the Earth and move forward to the present at the right. Both timelines will begin at the same place on the left side but will end at different points on the right. The timelines will be slightly over 5 meters long, or approximately 16½ feet. One meter on the timelines will equal 1.0 billion years. The upper timeline should start at 0
on the left and go up to 5 billion years on the right, with an arrow or ellipses showing that time increases further to the right, past the end of the timeline. Draw a horizontal line the length of the timeline toward the top of the paper leaving enough room at the top to write numbers above the tick marks. Make small vertical tick marks every 10 cm and larger vertical tick marks at each meter. Label the large marks 1.0 by. (billion years), 2.0 by., etc. up to 5.0 by. Label the small tick marks between 0 and 1.0 by. 100 my. (million years), 200 my., 300 my., etc., up to 900 my. (or 0.1 by., 0.2 by., etc., up to 0.9 by.). You do not need to label the small tick marks after 1.0 by. The lower timeline will begin at 4.6 bya. (billion years ago) at the left and end at NOW at the right under 4.6 by. on the upper timeline. Draw a horizontal line under the first timeline beginning at the same point on the left where the upper timeline begins but ending at the right 40 cm before the end of the upper timeline. Leave enough space to write numbers under the lower timeline. Draw a large vertical tick mark at the left end of the timeline and label it 4.6 bya. Draw 5 small tick marks at 10 cm intervals then another large vertical tick mark. Label this 4.0 bya. Then continue drawing small vertical tick marks every 10 cm and large tick marks every meter. Label the large tick marks 3.0 bya., 2.0 bya., 1.0 bya and NOW. Between 1.0 bya and NOW label the small tick marks 900 mya. (million years ago), 800 mya., 700 mya., etc., down to 100 mya. Between 500 mya. and 100 mya. add smaller tick marks every 50 cm to represent 50 million years, and between 100 mya. and NOW mark off every 1 cm to represent 10 million years. These smaller divisions do not need to be labeled since there is probably not enough room. If a thin enough marker is available you can mark off 5 mm divisions between 50 mya. and NOW to show 5 million year divisions, but care should be taken that the last 50 millions years does not become too crowded to make interpretation difficult. Begin the lesson. Part 1: Hang the double timeline in front of the class at a height that allows students to reach the lower timeline. Have students get in their groups. Distribute the timeline markers randomly to the groups. Not all groups will have the same number of markers, but each group should have at least one. Pass out copies of the short article The History of Life on Earth. Tell the students that their job is to determine where their marker(s) belongs on the timeline. A good way to do this is to read the article out loud. When the subject of a group s marker is mentioned in the article the group s communication officer should call out, Stop! The reading should stop while the communication officer tells the class what is on their marker and where it should go on the timeline. If the student is correct then he or she should affix the marker to the lower timeline at the correct point with tape, a pushpin or a thumbtack. (No markers should be placed on the upper timeline.) Teachers should check to ensure that the reader is stopped at the correct point and that markers are placed at the correct spot on the timeline. The markers and their correct times are as follows: First bacteria 3.8 bya First eukaryotes 1.8 bya First Multi-celled life 1.0 bya First hard bodies 570 mya
First vertebrates 500 mya First life on land 420 mya First true fish 420 mya First reptiles 360 mya First dinosaurs 245 mya First mammals 210 mya First primates 60 mya First hominids 5 mya First modern humans 100,000 years ago Students will need to estimate the correct placement of the markers on the timeline for many of these events. There is no tick mark for the last event, modern humans (Homo sapiens); the 100,000 year time interval is too small to show on this timeline. The marker should be placed under or just slightly to the left of NOW. Part 2 will take approximately 20 minutes, although many of the questions on the work sheet will make good discussion questions, which can increase the time devoted to this lesson. Both parts 1 and 2 can be done in a single lesson or, if time is running out, part 2 can be done separately as a follow up lesson. If dividing the two parts up into separate lessons, be sure to leave the timelines and the markers up. The groups will use them in Part 2. Pass out the worksheet for Lesson 8: The History of Life on Earth to the groups. The questions on the sheet should be discussed in the groups and responses recorded in the spaces provided. The first four questions can be used for a whole class discussion. Give the groups enough time to discuss and answer the worksheets, and then bring the whole class back together. You can begin the discussion by asking the communications officers to report the group s responses and then asking for other comments. Build Your Own Planet Lesson 8: The History of Life on Earth Group: Look at the timeline that the class has just assembled. Discuss the following questions with your group and record some ideas in the spaces below. [Answers in bold] Has life been complex or simple during most of Earth s history? [simple] (Complex means made up of many cells. Simple means made up of just one cell.) Has life been microscopic or macroscopic during most of Earth s history? [microscopic]
Has most life been in the oceans or on the land during most of Earth s history? [in the ocean] What are some things you notice about the way that life has evolved on Earth? [Many good answers are possible. Students may notice that life did not seem to change much for the first 2 billion years, that dinosaurs appear relatively recently, and that humans and hominids have only been around for a very short time] The work sheet concludes by asking students to find the age of their planet on the upper timeline and then imaging what the life on their planet might be like if it evolved at the same rate as life on Earth. They should look down from the upper timeline to the point directly below in on the lower timeline. Refer to lesson #5. How old is the star that your planet is orbiting? Assume that your planet is as old as your star. Above the timeline of Earth s history is another timeline. This one starts at 0 and goes up to 5 billion years. Find your planet s age on this timeline. If your planet is more than 5 billion years old, estimate how far beyond the end of the timeline your planet would be. If your planet is less than 4.6 billion years old: Look down from the upper timeline to Earth s timeline. Was there any life on Earth at that time? Yes / No (circle) If the answer is yes, think about what the life on Earth was like then. Where did it live? Ocean only / Land and ocean (circle) Was it:: simple, single-celled / complex, multi-celled (circle) How big was it? Microscopic / Macroscopic (circle) Had it developed any hard body parts yet? Yes / No (circle) Had it developed a backbone yet? Yes / No (circle)
Had it developed intelligence yet? Yes / No (circle) Students with planets younger than Earth should not have much difficulty determining what type of life might be on their planet. Any marker to the left of the point that marks their planet s age represents life that was already on Earth by that time. Markers to the right represent forms of life that had not yet evolved and can not be expected to exist on their planet. Students with planets less than 800 million years old will discover that Earth did not have any life that we know of at that point. The only way that life can exist there is if their planet has a very different early history from Earth. Students with planets older than Earth have a much more difficult task, because they will need to imagine how life on their planet might evolve beyond how it has on Earth. Students with planets, for example, 1 billion years older than Earth should look at how much life on Earth has changed in the last billion years to get some idea of how much more it might change in the next billion years. If your planet is greater than 4.6 billion years old: What is one way life on Earth has changed over the last 1 billion years? What is one way life on Earth has changed over the last 500 million years? What is one way life on Earth has changed over the last 5 million years? How much longer has life evolved on your planet than on Earth? How might life on Earth change that same length of time into the future? This next section should be completed by all groups. It is important to emphasize that these questions do not have right or wrong answers. Also, take a moment to reinforce the Two Important Points at the end of the lesson. All Groups: Pretend that life on your planet evolves at the same rate as life on Earth. What do you think it will be like when you explore the planet?
Where might you find it? What should you look for? Do you think it is likely that life on your planet will evolve at the same rate as life on Earth? Why or Why not? Two important points: 1) We have no way of knowing how rapidly life might evolve on other planets. Although it is possible that on some planets life might change at a rate similar to Earth s, there is no reason to assume that it must. On some planets it seems highly unlikely life would evolve at the same rate as Earth s. 2) Although life on a planet may evolve into complex, multi-celled forms, that does not mean that all life will be that way. On Earth, even though we have complex life forms like humans, trees, and fish, we still have a lot of simple, microscopic life around similar to some of the earliest things living on our planet. Today there are a lot more bacteria on Earth than mammals. These two points should be kept in mind as you search your planet for signs of life.
Appendix Standards Addressed Benchmarks (Grades 3 through 5) 1B Scientific Inquiry Scientists' explanations about what happens in the world come partly from what they observe, partly from what they think. Sometimes scientists have different explanations for the same set of observations. That usually leads to their making more observations to resolve the differences. 5C Cells Some living things consist of a single cell. Like familiar organisms, they need food, water, and air; a way to dispose of waste; and an environment they can live in. Microscopes make it possible to see that living things are made mostly of cells. Some organisms are made of a collection of similar cells that benefit from cooperating. Some organisms' cells vary greatly in appearance and perform very different roles in the organism. 5F Evolution of Life Fossils can be compared to one another and to living organisms according to their similarities and differences. Some organisms that lived long ago are similar to existing organisms, but some are quite different. 9D Uncertainty Some predictions can be based on what is known about the past, assuming that conditions are pretty much the same now. Events can be described in terms of being more or less likely, impossible, or certain. 9E Reasoning One way to make sense of something is to think how it is like something more familiar. 11C Constancy and Change Things change in steady, repetitive, or irregular ways-or sometimes in more than one way at the same time. Often the best way to tell which kinds of change are happening is to make a table or graph of measurements 12A Values and Attitudes Offer reasons for their findings and consider reasons suggested by others. 12E Critical-Response Skills Recognize when comparisons might not be fair because some conditions are not kept the same. Benchmarks (Grades 6 through 8) 5C Cells All living things are composed of cells, from just one to many millions, whose details usually are visible only through a microscope. Different body tissues and organs are made up of different
kinds of cells. The cells in similar tissues and organs in other animals are similar to those in human beings but differ somewhat from cells found in plants. 5F Evolution of Life Many thousands of layers of sedimentary rock provide evidence for the long history of the earth and for the long history of changing life forms whose remains are found in the rocks. More recently deposited rock layers are more likely to contain fossils resembling existing species. 6A Human Identity Fossil evidence is consistent with the idea that human beings evolved from earlier species. 11B Models Models are often used to think about processes that happen too slowly, too quickly, or on too small a scale to observe directly, or that are too vast to be changed deliberately, or that are potentially dangerous. 12B Computation and Estimation Estimate probabilities of outcomes in familiar situations, on the basis of history or the number of possible outcomes. 12D Communication Skills Read simple tables and graphs produced by others and describe in words what they show. Benchmarks (Grades 9 through 12) 5C Cells Within every cell are specialized parts for the transport of materials, energy transfer, protein building, waste disposal, information feedback, and even movement. In addition, most cells in multicellular organisms perform some special functions that others do not. The genetic information encoded in DNA molecules provides instructions for assembling protein molecules. The code used is virtually the same for all life forms. Before a cell divides, the instructions are duplicated so that each of the two new cells gets all the necessary information for carrying on. 5F Evolution of Life The basic idea of biological evolution is that the earth's present-day species developed from earlier, distinctly different species. The theory of natural selection provides a scientific explanation for the history of life on earth as depicted in the fossil record and in the similarities evident within the diversity of existing organisms. Life on earth is thought to have begun as simple, one-celled organisms about 4 billion years ago. During the first 2 billion years, only single-cell microorganisms existed, but once cells with nuclei developed about a billion years ago, increasingly complex multicellular organisms evolved.
Evolution builds on what already exists, so the more variety there is, the more there can be in the future. But evolution does not necessitate long-term progress in some set direction. Evolutionary changes appear to be like the growth of a bush: Some branches survive from the beginning with little or no change, many die out altogether, and others branch repeatedly, sometimes giving rise to more complex organisms. 11C Constancy and Change In evolutionary change, the present arises from the materials and forms of the past, more or less gradually, and in ways that can be explained. 12D Communication Skills Participate in group discussions on scientific topics by restating or summarizing accurately what others have said, asking for clarification or elaboration, and expressing alternative positions. National Standards (Grades 5-8) Structure and Function in Living Systems All organisms are composed of cells--the fundamental unit of life. Most organisms are single cells; other organisms, including humans, are multicellular. Diversity and Adaptations of Organisms Biological evolution accounts for the diversity of species developed through gradual processes over many generations. Species acquire many of their unique characteristics through biological adaptation, which involves the selection of naturally occurring variations in populations. Biological adaptations include changes in structures, behaviors, or physiology that enhance survival and reproductive success in a particular environment. National Standards (Grades 9-12) Biological Evolution Species evolve over time. Evolution is the consequence of the interactions of (1) the potential for a species to increase its numbers, (2) the genetic variability of offspring due to mutation and recombination of genes, (3) a finite supply of the resources required for life, and (4) the ensuing selection by the environment of those offspring better able to survive and leave offspring The great diversity of organisms is the result of more than 3.5 billion years of evolution that has filled every available niche with life forms. The millions of different species of plants, animals, and microorganisms that live on earth today are related by descent from common ancestors. Indiana Standards Grade 5 Science The Living Environment 5.4.2 Observe and describe that some living things consist of a single cell that needs food, water, air, a way to dispose of waste, and an environment in which to live.
5.4.8 Observe that and describe how fossils can be compared to one another and to living organisms according to their similarities and differences. Grade 6 Science The Nature of Science and Technology 6.1.2 Give examples of different ways scientists investigate natural phenomena and identify processes all scientists use, such as collection of relevant evidence, the use of logical reasoning, and the application of imagination in devising hypotheses and explanations, in order to make sense of the evidence. Scientific Thinking 6.2.6 Read simple tables and graphs produced by others and describe in words what they show. The Living Environment 6.4.3 Describe some of the great variety of body plans and internal structures animals and plants have that contribute to their being able to make or find food and reproduce. Common Themes 6.7.2 Use models to illustrate processes that happen too slowly, too quickly, or on too small a scale to observe directly, or are too vast to be changed deliberately, or are potentially dangerous. Grade 7 Science The Nature of Science and Technology 7.1.4 Describe that different explanations can be given for the same evidence, and it is not always possible to tell which one is correct without further inquiry. The Mathematical World 7.5.1 Demonstrate how a number line can be extended on the other side of zero to represent negative numbers and give examples of instances where this is useful. Grade 8 Science Scientific Thinking 8.2.7 Participate in group discussions on scientific topics by restating or summarizing accurately what others have said, asking for clarification or elaboration, and expressing alternative positions. Earth and Space Science ES.1.28 Discuss geologic evidence, including fossils and radioactive dating, in relation to Earth s past. Biology I B.1.12 Compare and contrast the form and function of prokaryotic and eukaryotic cells.
B.1.33 Describe how life on Earth is thought to have begun as simple, one-celled organisms about 4 billion years ago. Note that during the first 2 billion years, only single-cell microorganisms existed, but once cells with nuclei developed about a billion years ago, increasingly complex multicellular organisms evolved.