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Evolutionary Evidence Part 1: Fossil Record Bellringer • In your science journal, write and respond to the following question: –How do scientists learn about organisms of the past when studying fossils? Objectives: • I can define fossil and explain why fossils are important pieces of evolutionary evidence. • I can identify the different types of fossils. • I can explain how fossils are formed. • I can describe two methods to determine the age of fossils. • I can explain why the fossil record is incomplete • I can analyze components of the fossil record and determine the sequence in which the organisms appear. What are the different types of evidence used to support the evolutionary theory? There are several places we can see indirect evidence of evolution/evolutionary relationships: fossils, biogeography, similarities in anatomy, biochemistry/DNA, and embryology. What is a fossil and why is it important? • A fossil is any preserved evidence of an organism that lived long ago found in the Earth’s rocks. • Plants, animals, and bacteria can form fossils. • The fossil record shows that some species from long ago are extinct today. Other species alive today are similar to those in fossils. Why does the fossil record not provide as much evidence as the other components of evolutionary evidence? • There are missing links even in fossil record. • Approximately 99% of the species that have ever lived are now extinct, but only a tiny percentage of that was preserved as fossils. • Most organisms decompose before they have the chance to become fossilized. What are the different types of fossils? TYPES OF FOSSILS Fossils Types Formation A trace fossil is any indirect evidence Trace fossils Casts left by an animal and may include a footprint, a trail, or a burrow. When minerals in rocks fill a space left by a decayed organism, they make a replica, or cast, of the organism. A mold forms when an organism is Molds Petrified fossils Amber-Preserved or frozen fossils buried in sediment and then decays, leaving an empty space. Petrified-minerals sometimes penetrate and replace the hard parts of an organism At times, an entire organism was quickly trapped in ice or tree sap that hardened into amber. What are the different types of fossils? • Trace fossils – footprints, burrows, feces • Molds and casts – impressions or a mold filled with sediment • Replacement – original material replaced with mineral crystals • Petrified or Permineralized – empty pores are filled in by minerals • Amber – tree sap preserved • Original material – mummification or freezing What are transitional fossils and why are they important? • Charles Darwin predicted that scientists would find fossils that would show organisms that were intermediates between different species. • Scientists today have found thousands of transitional fossils that contain features shared by different species. • Scientists have found intermediate species for the evolution of mollusks, modern horses, whales, and humans. What are the classes of transitional fossils? • 2 major classes of transitional fossils: – Derived traits – Ancestral traits • Derived traits are newly evolved features, such as feathers, that do not appear in the fossils of common ancestors. • Ancestral traits are more primitive features, such as teeth and tails, that do appear in ancestral forms. Who studies fossils? • Paleontologists, scientists who study ancient life, are like detectives who use fossils to understand events that happened long ago. • They use fossils to determine the kinds of organisms that lived during the past and sometimes to learn about their behavior. How are fossils formed? • For fossils to form, organisms usually have to be buried in mud, sand, or clay soon after they die. • Fossils are not usually found in other types of rock because of the ways those rocks form. • Most fossils are found in sedimentary rocks. rocksthe form at relatively low temperatures and pressures • These For example, conditions under which metamorphic rocks form often that may damage to the organism. destroy anyprevent fossils that were in the original sedimentary rock. How are fossils formed? • Fossils do not form in igneous or metamorphic rock; they will not survive the heat or pressure involved in the formation of these kinds of rocks. • Fossils are formed in sedimentary rock. Why is it that not all organisms become fossils? • Few organisms become fossilized because, without burial, bacteria and fungi immediately decompose their dead bodies. • Occasionally, however, organisms do become fossils in a process that usually takes many years. “How fossils form” Right click the above link and open the hyperlink to look at an interactive lesson on fossil formation What are the methods in which scientists use to determine the age of a fossil? • Relative dating • This method is used to determine the age of rocks by comparing them with those in other layers • This method basically indicates that the fossils found closer to the surface are younger, and the fossils found in deeper strata are • This method does not more primitive (older)(in give a specific age of undisturbed ground) the fossil or rock. What are the methods in which scientists use to determine the age of a fossil? RELATIVE DATING What are the methods in which scientists use to determine the age of a fossil? • Using this principle of relative dating, scientists can determine relative age and the order of appearance of the species that are preserved as fossils in the layers. • The law of superposition states that younger layers of rock are deposited on top of older layers. What are the methods in which scientists use to determine the age of a fossil? • Radiometric dating • This method uses the decay of radioactive isotopes of atoms to measure the absolute age of a rock. • To find the specific ages of rocks, scientists use absolute dating, also called Radiometric Dating. • As specific atoms decay they emit radiation and lose electrons, which causes them to turn into a different element. • So- these atoms change from one thing into something else over time- and they do this at a constant rate. What are the methods in which scientists use to determine the age of a fossil? • The half-life of a radioactive atom is the time it takes for half of that atom in a sample to decay and turn into another element. • Radioactive isotopes are found in igneous and metamorphic rock, not sedimentary, and cannot be used to date fossils. • If you know what the unstable atom is (Carbon 14) and you know what it turns into as it decays (Nitrogen 14). • And you know the rate at which the unstable atom decays/turns into something else It takes 5,730 years for ½ of Carbon 14 to turn into Nitrogen 14 • You can measure the amount of the unstable atom in the rock….and compare that to the amount of the new atom • This will tell you the age of the sample rock. Most radioactive isotopes have rapid rates of decay (that is, short half-lives) and lose their radioactivity within a few days or years. Some isotopes, however, decay slowly, and several of these are used as geologic clocks. The parent isotopes and corresponding daughter products most commonly used to determine the ages of ancient rocks are listed below: Parent Isotope Stable Daughter Product Currently Accepted Half-Life Values Uranium-238 Lead-206 4.5 billion years Uranium-235 Lead-207 704 million years Thorium-232 Lead-208 14.0 billion years Rubidium-87 Strontium-87 48.8 billion years Potassium-40 Argon-40 1.25 billion years Samarium-147 Neodymium-143 106 billion years What is stasis? • Stasis is the term used to describe a period of time during which organisms don’t seem to change their forms during a lengthy presence in the fossil record. What can an incomplete fossil record indicate? • The sudden disappearance of many life forms in the fossil record suggests that a mass extinction occurred. For those species that survived a mass extinction, new ecological niches became available. This may have led to rapid evolution, which would appear to be a “sudden appearance” in the fossil record of many different species, also known as adaptive radiation What is adaptive radiation? • Adaptive radiation - the evolutionary division of a group of organisms into diverse groups over a short period of geologic time