Fossils and Evolution PDF

How do fossils form? Evidence that organisms have changed over time can be found in amber, ice, or sedimentary rock. Sedimentary rock is formed when particles of sand or soil are deposited in horizontal layers. Often this occurs as mud or silt hardens. After one rock layer forms, newer rock layers...

How do fossils form? Evidence that organisms have changed over time can be found in amber, ice, or sedimentary rock. Sedimentary rock is formed when particles of sand or soil are deposited in horizontal layers. Often this occurs as mud or silt hardens. After one rock layer forms, newer rock layers form on top of it. So, older layers are found below or underneath younger rock layers. The most basic principle of dating such rocks and the remains of organisms inside is "the deeper it is, the older it is." A) Many Fossils Form in Sedimentary Rock: Rock layers preserve evidence of organisms that were once alive. The remains or imprints of once-living organisms are called fossils. Fossils commonly form when a dead organism is covered by a layer of sediment or mud. Over time, more sediment settles on top of the organism. Minerals in the sediment may seep into the organism and replace the body's material with minerals that harden over time. This process produces a cast fossil. Many familiar fossils are casts of hard parts, such as shells and bones. If the organism rots away completely after being covered, it may leave an imprint of itself in the rock. Despite all of the fossils that have been found, it is rare for an organism to become a fossil. Most often, the dead organism is recycled back into the biological world by scavengers, decomposers, or the process of weathering. How do fossils show change over time? All of the fossils that have been discovered make up the fossil record. The fossil record provides evidence about the order in which species have existed through time, and how they have changed over time. By examining the fossil record, scientists can learn about the history of life on Earth. Despite all the fossils that have been found, there are gaps in the fossil record. These gaps represent chunks of geologic time for which a fossil has not been discovered. Also, the transition between two groups of organisms may not be well understood. Fossils that help fill in these gaps are transitional fossils. The illustration on the right is based on a transitional fossil. Fossils found in newer layers of Earth's crust tend to have physical or molecular similarities to present-day organisms. These similarities indicate that the fossilized organisms were close relatives of the present-day organisms. Fossils from older layers are less similar to present-day organisms than fossils from newer layers are. Most older fossils are of earlier life-forms such as dinosaurs, which don't exist anymore. What other evidence supports evolution? Many fields of study provide evidence that modern species and extinct species share an ancestor. A common ancestor is the most recent species from which two different species have evolved. Structural data, DNA, developmental patterns, and fossils all support the theory that populations change over time. Sometimes these populations become new species. Biologists observe that all living organisms have some traits in common and inherit traits in similar ways. Evidence of when and where those ancestors lived and what they looked like is found in the fossil record. A) Common Structures Scientists have found that related organisms share structural traits. Structures reduced in size or function may have been complete and functional in the organism's ancestor. For example, snakes have traces of leglike structures that are not used for movement. These unused structures are evidence that snakes share a common ancestor with animals like lizards and dogs. Scientists also consider similar structures with different functions. The arm of a human, the front leg of a cat, and the wing of a bat do not look alike and are not used in the same way. But as you can see, they are similar in structure. The bones of a human arm are similar in structure to the bones in the front limbs of a cat and a bat. These similarities suggest that cats, bats, and humans had a common ancestor. Over millions of years, changes occurred. Now, these bones perform different functions in each type of animal. B) Similar DNA The genetic information stored in an organism's DNA determines the organism's traits. Because an organism's DNA stays almost exactly the same throughout its entire lifetime, scientists can compare the DNA from many organisms. The greater the number of similarities between the molecules of any two species, the more recently the two species most likely shared a common ancestor. Recall that DNA determines which amino acids make up a protein. Scientists have compared the amino acids that make up cytochrome c proteins in many species. Cytochrome c is involved in cellular respiration. Organisms that have fewer amino acid differences are more likely to be closely related.  ************************************** Fossil Evidence: Scientists have examined fossils of extinct species that have features in between whales and land mammals. These features are called transitional characters. None of these species are directly related to modern whales. But their skeletons suggest how a gradual transition from land mammal to aquatic whale could have happened. A) Pakicetus 52 million years ago: whale-shaped skull and teeth adapted for hunting fish. ran on four legs. ear bones in between those of land and aquatic mammals. B) Ambulocetus natans 50 million years ago: name means "the walking whale that swims". hind limbs that were adapted for swimming. a fish eater that lived on water and on land C) Dorudon About 40 million years ago: lived in warm seas and propelled itself with a long tail. tiny hind legs could not be used for swimming. pelvis and hind limbs not connected to spine could not support weight for walking. Unused Structures: Most modern whales have pelvic bones and some have leg bones. These bones do not help the animal move. ***********************************  Fossils show us what a dinosaur looks like. This dinosaur lived millions of years ago! Fossil: is the remains or trace of once-living organisms. Record: is an account that preserves information about facts or events. This is a Petoskey stone, which is made up of tiny coral fossils. What can you infer if you find a coral fossil on land? This flying dinosaur is an example of a cast fossil. Amber fossils form when small creatures are trapped in tree sap and the sap hardens. Because this woolly mammoth was frozen in ice, its skin and hair were preserved. A transitional form between fish and four-legged land vertebrates may be this creature called Tiktaalik roseae. Describe the environment in which this organism lives. How is this organism like both a fish and a four-legged vertebrate, such as an amphibian? Do you see any similarities between the bones of the bat and cat limbs and the bones of the human arm? If so, use the colors of the bat and cat bones to color similar bones in the human arm. If you don't have colored pencils, label the bones with the correct color names. What is a common ancestor? Cat and chicken embryos are at a similar stage of development. Both has similar body shape and has head, eyes and limb buds. Molecular Evidence: The DNA of whales is very similar to the DNA of hoofed mammals. Below are some DNA fragments of a gene that makes a type of milk protein. Circle the pairs of nitrogen bases (G, T, C, or A) that differ between the hippopotamus and humpback whale DNA: 1) Hippopotamus: (TCC TGGCA GTCCA GTGGT). 2) Humpback whale (CCC TGGCA GTGCA GTGCT). - Modern Whale Present day: no hind limbs, front limbs are flippers. some whales have tiny hip bones left over from. their hoofed-mammal ancestors. breathe air with lungs like other mammals do. - How do you think these bones are involved in a whale's movement? - Analyze Examine the four skeletons. Indicate which species appears to be best adapted for swimming underwater for a long time. Which characters allow the animal to behave this way? - How does the fossil record provide evidence of the diversity of life? - Fossil evidence shows that life on Earth has changed over time. - The remains of once-living organisms are called fossils / ancestors. - Evolutionary theory is also supported by structural, genetic, and developmental evidence. - Similarities / Differences in internal structures support evidence of common ancestry. - Scientists use evidence from many fields of research to study the common ancestors of living organisms. - The tiny leg bones / large dorsal fins of modern whales are an example of unused structures. - Which word means “the remains or imprints of once-living organisms found in layers of rock?” - Which word means “the history of life in the geologic past as indicated by the imprints or remains of living things?”. - Identify What are two types of evidence that suggest that evolution has occurred? - Explain How do fossils provide evidence that evolution has taken place? - Apply What is the significance of the similar number and arrangement of bones in a human arm and a bat wing? - Imagine If you were a scientist examining the DNA sequence of two unknown organisms that you hypothesize share a common ancestor, what evidence would you expect to find? - Fossils provide evidence of organisms that lived in the past (True / False). - The wing of a bat has similar bones to those in a human arm (True / False). - DNA can tell us how closely related two organisms are (True / False). - Whales are descended from land-dwelling mammals (True / False). *********************************** - What common structures in this picture indicate? *********************************** Cytochrome C comparison organism Number of amino acid differences from human cytochrome c Chimpanzee 0 Rhesus monkey 1 Whale 10 Turtle 15 Bullfrog 18 Lamprey 20 The number of amino acids in human cytochrome c differs between humans and the species at left. Which two species do you Are the least closely related to humans?