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Science Study Guide – Lesson 2 - INSIDE LIFE Chapter 6 – EXPLORING CHANGE Part 2 of 2 - CONCEPTS (2/5/07 – 3/07/07) Learning Log – Your Learning Log, which is your “test aid” should contain the following PRIMARY CONCEPT followed by the 4 SUPPORTING CONCEPTS AS NOTED BELOW: PRIMARY CONCEPT – Evolution explains the diversity of life on Earth SUPPORTING CONCEPTS: 1. Organisms change across time 2. Natural selection explains how species change across time 3. Multiple lines of evidence that confirm evolution 4. Physical properties change, meaning, Earth’s physical environment changes over time Note – Items in this study guide that should be included on your learning log will be followed by the following notation - **Learning Log recommended** 1. Unity and Diversity – Understand that living organisms are similar, (Unity), in that they all are made up of cells, have DNA within those cells, may share similar physical features such as having hair, having wings, having 2 or 4 legs, living in water, and so forth. Understand also that living organisms are different, (Diversity), in that many organisms differ widely in physical appearance, in the environment they live in, the fact that animals must consume their food while plants manufacture their own food, some fly, some walk and some swim. The concept of Unity and Diversity includes an understanding that living things can be organized both according to their similarities and their differences. 2. Fossil Records Provide Evidence of Evolution – Fossil records help provide evidence of evolution by preserving organisms that lived in past eras. Using rock layers to determine the relative age of fossils, we can compare the characteristics of these organisms to other fossils found in the same layers, in different layers and to organisms that are living today. Similarities in characteristics across time provide evidence of evolution. Additionally, fossil records provide evidence of environmental shifts over time such as changes from desert to ocean to forest which in turn might show how organisms have evolved to survive during these environmental shifts. *** Learning Log Summary Recommended *** 3. Rock Layers and Relative Dating – Rock layers occur naturally across time in a predictable sequence with the oldest layers at the bottom and newer layers toward the top. Fossils found in various rock layers help us to identify organisms that are similar in age to each other and they also allow us to compare these organisms to each other and to organisms from both older and more current times. Rock Layers provide the Relative Age of fossils because we know that fossils found in a rock layer are the same relative age as the rock layer itself, and we also know that fossils found in deeper layers are older than fossils found in higher layers. Additionally, rock layers allow us to identify environmental shifts across time in the same geographic area. Comparing fossil characteristics such as similarities, differences or modifications, along with the ability to identify environmental changes provide strong evidence of evolution across time. 4. Absolute Dating – Absolute Dating is accomplished using the principles of Radiometric or Radio Carbon Dating. These procedures use the scientific analysis of Radioactive Isotopes as they decay from Parent to Daughter elements and then comparing the amount of each element against the known Half Life of the Parent element to determine the exact age of minerals or fossils. Radiometric Dating is used to determine the absolute age of minerals and Radio Carbon dating is used to determine the absolute age of previously living organisms. **** Learning Log summary is recommended, include all bolded terms *** 5. Understanding Absolute Dating – reference the examples below: 1. If you started with 50g of Uranium 235 which has a Half Life of 710 million years, how much would you have left after 5,680,000,000 years? Answer – With a Half Life of 710 million years, the uranium 235 would decay a Total of 8 Half Lives in 5,680,000,000 years, (5,680,000,000 / 710 = 8 Half Lives) The amount of Uranium 235 would decrease by half for EACH Half Life, (50 divided by 2 to the 8th power), or as follows: 50g to 25g to 12.5g to 6.25g to 3.125g to 1.5625g to .278125g to .390625g and finally to .1958125g after 8 half lives. 2. - Suppose you find a rock with 3 times as much Argon 40 as Potassium 40, How old is the rock? Potassium 40 decays to Argon 40 with a Half Life of 1.3 Billion years. (Answer on Next Page) Answer – After one Half Life, you would have 50% of Potassium 40, and 50% of Argon 40, or EQUAL amounts of each. After the next Half Life, you have 25% of 25% of Potassium 40 and 75% of Argon 40 which means you now have 3 times as much Argon 40 as you have Potassium 40, (25% VS 75%) You can conclude that 2 Half Lives have passed or a total of 2.6 Billion years, the rock is 2.6 billion years old. 6. Effects that Variation in Characteristics have on Survival – Different characteristics of individuals within a species, or different characteristics between various species can both effect the survival of those species across time. Variations such as color, size, or speed within a species can affect the ability of that species to avoid predators which allows greater numbers of those individuals with the more favorable characteristics to reproduce in greater numbers, increasing these favorable characteristics within the species and thus, improving their chances for survival over time. Similarly, variations in characteristics between similar species, such as the different types of beaks that birds might have, might affect their ability to eat available food sources. Changes in environments that effect food sources could favor the survival of species that have characteristics that make them more able to eat a greater variety of food. Species with these characteristics will reproduce in greater numbers, increasing these favorable characteristics and thus, improving their chances for survival over time. EXAMPLES OF Variations – 1. If LARGE RED INSECTS and TINY GREEN INSECTS within the same species of insects both live in a green, grassy field and are both considered as a good food source for the SPOTTED INSECT EATER, it is likely that the VARIATION in the size and color of the insects will result in the Large Red Insects being eaten more often. This Variation is a favorable characteristic for the Tiny Green Insect and might eventually result in the reduction or extinction of the Large Red Insect and a population that has many more Tiny Green Insects. 2. If two species of Spotted Insect Eaters live in the forest and one species has a long nose, a long tongue and claws on its feet and the other species has a short nose, a short tongue and webbed feet, what would happen if all of the insects in the forest live inside hollow logs? The VARIATION in the species of Spotted Insect Eaters would most likely result in the long nosed species having success in catching and eating insects while the short nose version would have trouble finding food. This VARIATION in characteristics might eventually result in the reduction or extinction of the short nose species and the survival of the long nosed version in larger populations. 7. Natural Selection Explains How Species Change Over Time – Natural Selection is the process by which favorable traits or characteristics are able to be passed on to future generations through the reproductive process. (These are traits or characteristics that are coded in the genes of a species and are able to be passed on from generation to generation through natural reproduction) Organisms that have favorable traits, such as color, size, and speed, or predators that are “generalists” in that they can catch and eat a wide variety of prey, are more likely to survive and reproduce in larger numbers than those organisms with unfavorable traits or characteristics. Selective Pressure is the term that is used to explain the pressure that a predator places on its Prey to survive, or the pressure that is placed on predators when they must compete for a limited or specific type of Prey. Natural Selection explains how species change over time because it provides species with favorable traits a greater ability to survive the selective pressure across a wider variety of long term catastrophic or environmental changes. In addition to having a greater chance for survival, natural selection over long periods of time, (many generations), may actually lead to even stronger favorable traits through adaptations or modifications within the genes, providing more evidence that species change over time. *** Learning Log entry is recommended, include all bolded items. *** Examples of NATURAL SELECTION and SELECTIVE PRESSURE 1. Reference Example #1 of VARIATION on Concept 6 above. The survival of the Tiny Green Insect is an example of Natural Selection, where the favorable characteristics of the variation result in survival and growth of the organism with the favorable characteristics. In this example, the Selective Pressure is provided by the Spotted Insect Eater and the Natural Selection favors the survival of the Tiny Green Insect. 2. Reference Example #2 of VARIATION on Concept 6 above. The survival of the Long Nose Insect Eater is an example of Natural Selection, where the favorable characteristics of the variation results in survival and growth of the organism with the favorable characteristics. In this example, Selective Pressure is provided by the insects that only live in hollow logs and the Natural Selection favors the Insect Eater with the long nose that can reach the insects in the hollow logs. 8. Darwin’s Evidence and Observations from his 5 year journey – During Darwin’s journey that began in 1831, he collected thousands of specimens and recorded extensive notes about his journey. Many of these key observations and the evidence he collected and wrote about helped him to support his theories about how life changes over time and were the basis for his theory of Evolution. Some examples of his observations are as follows: a. Plants and animals have adaptations, which are characteristics that help organisms survive and reproduce in particular environments. b. Some species have similar body structures that are adapted for different purposes. Examples: Wings of Penguins are used as flippers, wings of Rheas are used as sails, wings of the Steamer Duck are used as paddles while the majority of bird wings are used to fly c. Organisms living in temperate areas of one continent were more similar to organisms living in tropical areas on the same continent than they were to organisms living in temperate areas on different continents. This led him to believe that in Geographical Distribution, similar species came from a common ancestor that lived in the same geographical area rather than from a particular environment that may be similar in many different geographical areas on different continents. d. Many fossils look similar to existing species e. Younger rock layers had more fossils that were similar to existing species than did older rock layers. (meaning older rock layers contained more fossils of organisms that no longer existed) 9. Understanding Darwin’s Theory of Evolution – Evolution provides an explanation for how species change across time. Evolution only occurs when there are variations in populations and when there are selective pressures acting on those variations. For example, some individuals within a population might have variations in one or more characteristics. Selective pressures cause individuals with beneficial characteristics, also called adaptations, to survive and cause individuals without the adaptations to die off. This process is called natural selection. Across time, more of the individuals with the adaptations survive and reproduce. As more of the populations have the adaptations, eventually the population can be recognized as a distinct new species. ***** Learning Log entry is recommended. A complete explanation of evolution should include all of the bolded words in this concept.