TIME LINE OF LIFE Material Time Line of Life Working Time Line of Life Clock of Eras Strip for Clock of Eras representing the circumference Elastic strip for Clock of Eras Presentation 1: Overview 1. Review the eras represented on the Clock of Eras: A. Precambrian Era B. Paleozoic Era C. Mesozoic Era D. Cenozoic Era 2. Take the strip of Clock of Eras and place it around the circumference of the clock. Note the color relationship. 3. Place the Clock of Eras to the side. Lay the strip before the children and review the eras represented linearly. 4. Take the elastic and place it parallel to the strip of Clock of Eras. Note the similarity of the two strips: they represent the same geological intervals. 5. Say, Today we are going to look at the time since life has been on the earth. We will stretch out the Paleozoic, Mesozoic, and Cenozoic Eras and look at this time in some detail. Then, stretch that portion of the elastic represented by these eras. Montessori Research and Development 2006 2
6. Say, I have a long chart that represents these eras and can tell us more about these times. Then lay out the Time Line of Life. 7. Begin the analysis of the Time Line of Life by reading the era titles at the top. Begin at the left: A. The top blue strip is the Paleozoic Era. It is the longest. B. Next is the brown strip representing the Mesozoic Era. C. Finally, the Cenozoic Era is represented in green. 8. Proceed to analyze the second row on the chart. Under the eras, geological time is divided into periods. The Paleozoic Era has six Periods: A. Cambrian Period B. Ordovician Period C. Silurian Period D. Devonian Period E. Carboniferous Period (in the United States this period is divided into Mississippian Period and Pennsylvanian Period.) F. Permian Period The Mesozoic Era has three Periods: A. Triassic Period B. Jurassic Period C. Cretaceous Period Montessori Research and Development 2006 3
The Cenozoic Era has two Periods: A. Tertiary Period B. Quaternary Period 9. Proceed to analyze the third row on the chart. All the Periods are further divided into Epochs. However, only the Cenozoic Era is treated on this chart: Tertiary Paleogene Period: A. Paleocene Epoch B. Eocene Epoch C. Oligocene Epoch Tertiary Neogene Period: D. Miocene Epoch E. Pliocene Epoch Quaternary Period: F. Pleistocene Epoch G. Holocene Epoch 10. Proceed to analyze the fourth row on the chart. This is a descriptive treatment called Ages. The Paleozoic Era has three Ages: A. Age of Invertebrates Discuss the meaning of invertebrates, reviewing the first nine phyla Montessori Research and Development 2006 4
B. Age of Fish Discuss the meaning of fish, reviewing the chordata phylum on the Animal Kingdom Chart. C. Age of Amphibians Discuss the meaning of amphibian, reviewing the chordata phylum The Mesozoic Era has one Age: A. Age of Reptiles Discuss the meaning of reptile, reviewing the chordata phylum The Cenozoic Era has one Age: A. Age of Mammals Discuss the meaning of mammal, reviewing the chordata phylum 11. On a fifth row under Invertebrates is: A. Age of Trilobites. These were the most important animals early in the Age of Invertebrates. B. Age of Crinoids. These were animals (echinodermata) whose skeletons covered the bottom of the ocean. 12. Note the ice represented on the Time Line of Life. There are four and they represent the four great glacial periods. A great part of the earth was covered with ice during these periods. Montessori Research and Development 2006 5
13. Note the red lines that rise and fall and some that disappear. These lines represent the appearance, ascendance, decline, or disappearance of various animals. A. The trilobites appear, exist for a time, decline, then disappear. 14. Note the many animals. They will be discussed later. 15. Note the mountains. They represent changes in the earth s surface. NOTE: When the child can repeat the information given at the presentation of the Time Line of Life, the second presentation is given. Presentation 2: Detailed Exploration Review the first row of the chart: Eras. Proceed to analyze in detail the Periods listed on the second row. Paleozoic Era 1. Cambrian Period: Cambrian comes from the Roman name for Wales, Cambria, where the first fossils of this period were found. The Cambrian Period was dominated by trilobites. Brachiopods were present and second in abundance, but neither very diverse nor common. Trilobites played a variety of foodgathering roles in the Cambrian. Many of them were probably detritus feeders, moving sluggishly across the sea floor. Others were probably shallow burrowers, but still obtaining food from the sediment. Still others may have been feeble swimmers, using their appendages to direct foodladen currents to the mouth, much like some living crustaceans, such as fairy shrimp. They formed simple communities. Montessori Research and Development 2006 6
The abundance of trilobites is enhanced by the fact that they grow by casting off their exoskeleton in a series of molt stages. Thus, one animal might have produced ten or twelve potentially preservable skeletons during its lifetime. Trilobites had a considerable size range from a few millimeters long to 20 to 30 centimeters in length. Some trilobites had large compound eyes, whereas others had no traces of eyes. The exterior was very smooth, plain, and streamlined, or highly ornamented with spines and nodes. Some of the spiny forms may have been active swimmers, the spines making it easier for them to move through the water. Still other trilobites could curl up so that the tip of the tail and the head met. This may have been a defensive posture; if so, it suggests that there were predators that fed on trilobites. After the Cambrian, trilobites became a subordinate part of most marine communities. They continued to evolve, but were limited to only a few groups. They gradually became extinct, many at the close of the Ordovician; still others at the end of the Devonian. By the late Paleozoic only a few species remained, persisting until near the close of the Paleozoic, when they, too, became extinct. 10 10 Lane, Life of the Past, page 152. 2. Ordovician Period: The Ordovician Period is named for an early Celtic tribe in Wales, the Ordovices, where the first fossils of this period were found. Beginning in the Ordovician, a strikingly different kind of marine community came into existence that persisted until the close of the Permian, a time span of over 200 million years. The dominant members of these communities Montessori Research and Development 2006 7