Evidence of Evolution

Scientists look at many different fields of study to find evidence in support of evolution. In this WizerMe you will explore how 3 fields of study provide support for evolution, the change of species over time. The 3 fields are: 1. Fossils Radioactive Dating 2. Embryology 3. Comparing the bodies of animals (homologous structures) Evidence of Evolution Use the video to answer the 5 questions below 1. What are the four major categories for evidence for evolution? 2. From the video above: how does the law of superposition help us determine the age of various fossils? 3. What is a homologous structure? 4. What is a vestigial structure? 5. What is the study of embryology? Read the article and click on the blank to select the correct word. Evolution is the theory that organisms gradually change over time. This theory has been thoroughly tested and there is enough conclusive data that evolution occurred in the past and continues to take place today. Several types of evidence support the theory of evolution, including homologous structure, early development, similarities in DNA, and the fossil record.Homologous structures are body structures (ex. bone structures) that are similar and shared by two or more organisms. These structures have helped us to classify vertebrate organisms including fish, amphibians, reptiles, birds, and mammals which all share a similar internal skeleton with a backbone. Homologous structures help to show how certain species may have inherited a trait from an ancestor.Similarities in embryological development can also provide evidence for evolution. Observing embryos of different species during various stages of early development can reveal similarities. Many different species share similar structures early on such as tails or gill slits, which demonstrates relationships and reveals common ancestors. The more structures they have in common, the more closely related the organisms.We can also compare the DNA of organisms to note how many nitrogen base pairs (A-T; C-G) are the same. The more bases that match, the more similar two organisms are to one another. Because bases along a gene call for specific proteins to be created, scientists can compare the order of amino acids in a protein to see how similar species are.Fossils provide “hard” evidence that organisms of today originated from a common ancestor and changed over time. Unfortunately, the evolutionary history of the earth and it’s fossil record is incomplete because many organisms don’t leave behind fossils, creating gaps or “missing link." A missing link is a transitional fossil or species that exhibits traits common to both an ancestral group and its descendants. For example, the discovery of the Archaeopteryx bridged the gap between dinosaur and present day birds, such as chickens. Depending on where and how an organism dies, fossils can be created in several forms. Some fossils are formed when organisms die and become buried in sediments, such as soil or rock. Layers of sediment cover over dead organisms and over millions of years, the layers can harden to become sedimentary rock. Preserved remains occur when an organism becomes trapped in substances other than sediments, like amber of ice. Petrified fossils occur when remains are buried and the remains are gradually replaced by minerals, changing them into rock. When hard remains like shells are buried in sediment, they gradually dissolve, leaving behind a hollow space called a mold. As that mold becomes filled by hardened minerals, it becomes a cast.In order to better understand how organisms change over time, we need to be able to determine the order in which the events occurred, the age of fossils, and how one fossil of a species compares with another fossil of the same species. There are two ways of determine the age of fossil evidence. If rock layers are preserved in the original sequence, scientist use relative dating. The older a fossil is, the lower in the rock layer it will be found. Organisms that resemble the living creatures of today are mostly found in the top layers, while more ancestral forms are found in lower layers. However, relative dating does not help to determine the actual age of a fossil.Absolute dating is used to determine the times in which various organisms lived. The process can use both the actual fossil or rocks found near the fossil to estimate how long ago an organism lived. Absolute dating can provide additional evidence that different organisms are related. Radioactive dating is a type of absolute dating where scientist use different radioactive elements to estimate when an organism lived. These elements are unstable and decay or break down into other elements over time. Their half-life is the time it takes for half of the atoms in a sample to decay. Scientist can observe how much of each element is present in a sample and compare that to the half-life to determine how much time has passed. Evolution Reading: Matching Evolution Organisms gradually change over time Homologous Structure Similar body structure (ex. bones) that are shared by two or more organisms Embryonic Development Similarities in embryos show evolutionary relationshis DNA Similarities in the genetic code between organisms shows an evolutionary relationship Fossils Show a pattern of how organisms have changed over time Preserved Remains When an organism dies and its remains are trapped in tar, ice, or amber Radioactive Dating When radioactive elements are used to determine the age of a fossil Half-Life The amount of time it takes for half of a radioactive atoms to decay Carbon Dating Watch the video as a refresher on carbon dating. Remember - Log in with G-Suite for Education! Brain Pop: Carbon Dating Half-Life Problems Background Information Radioactive dating is a type of absolute dating. To perform this process, scientist use many different radioactive elements which are unstable and decay or break down over time. A half-life is the amount of time it takes for halfof the atoms in a radioactive sample to decay.Ex. If the half life of Carbon-14 is 5,700 years, how much carbon remains in a sample after 11,400 years if there was originally 60 grams? Answer: 11,400 years is two half-lives (5,700 x 2) so we dived 60 g twice. 60 = 30; 30 = 15 g of carbon remainsEx. A sample of rock is found to have 20g of Carbon-14. If two half lives have passed, how much carbon was in the sample originally? Answer: Half life 1: 20g x 2 = 40g Half life 2: 40g x 2 = 80g in the sampleoriginally Looking at the diagram below, on one side describe how the bones are SIMILAR in shape, on the other describe how the bones are DIFFERENT in shape for the 4 animals. Create your own make believe limb using the same color coding as the diagram above. Consider the placement of the various bones along with the function of the limb itself. Make sure that your limb is colored appropriately and explain what your limb does for your organism. You may complete this diagram on paper and turn in to your teacher. Use the image of embryonic development below to answer the questions that follow. In stage 1 of development, how many organisms seem to share the same characteristics as the human embryo? Only 1 The first 3 animals Only the mammals All of the organisms In stage 2, which organisms do NOT share similar characteristics as the human? Fish Salamander Fish and Salamander All of the organisms What happens to the embryos in stage 3 of development? How does looking at the embryonic stages of animals help scientist to determine evolutionary relationships? Reflection After watching the video above: write down 4 things that you have learned about how scientists use fossils, embryology, homologous structures, and DNA as evidence for evolution.