Fossils. Who studies fossils? How do fossils form? Fossils are the preserved remains or traces of living things.

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1 Fossils Essential Questions: What are fossils and how are they formed? What are the different kinds of fossils? What do fossils tell about how organisms have changed over time? Who studies fossils? Scientists who study fossils are called paleontologists. All the info that paleontologists have gathered about past life is called the fossil record. How do fossils form? Fossils are the preserved remains or traces of living things. Fossils provide evidence of how life has changed over time. Fossils also help scientists infer how Earth s surface has changed. Fossils are clues to what past environments were like. 1

2 How do fossils form? Most fossils form when living things die and are buried by sediments. The sediments slowly harden into rock and preserve the shapes of the organisms. HOW IS A FOSSIL FORMED? 1. Sediment An animal is buried by sediment, such as volcanic ash or silt, shortly after it dies. Its bones are protected from rotting by the layer of sediment. 2. Layers More sediment layers accumulate above the animal s remains, and minerals, such as silica (a compound of silicon and oxygen), slowly replace the calcium phosphate in the bones. 3. Movement Movement of tectonic plates, or giant rock slabs that make up Earth s surface, lifts up the sediments and pushes the fossil closer to the surface. 4. Erosion Erosion from rain, rivers, and wind wears away the remaining rock layers. Eventually, erosion or people digging for fossils will expose the preserved remains. 2

3 What conditions promote fossilization? Hard body parts such as skeletal bones or exoskeletons What conditions promote fossilization? Rapid burial and/or lack of oxygen How do fossils form? Fossils are usually found in sedimentary rock. Sedimentary rock is the type of rock that is made of hardened sediment. 3

4 What are the different kinds of fossils? Fossils found in rock include: petrified fossils, molds and casts, carbon films, and trace fossils. Other fossils forms called preserved remains are found when the remains of organisms are preserved in substances such as: tar, amber, or ice. FIVE MAIN TYPES OF FOSSILS Petrified Fossils Molds and Casts Carbon Films Trace Fossils Preserved Remains PETRIFIED MOLD CAST 4

5 What are the different kinds of fossils? Petrified Fossils A fossil may form when the remains of an organism become petrified. Petrified means turning to stone Petrified fossils are fossils in which minerals replace all or part of an organism. What are the different kinds of fossils? Molds and casts A mold is a hollow area in sediment in the shape of an organism or part of an organism. A mold forms when the hard part of the organism such as a shell, is buried in sediment. A cast is a copy of the shape of an organism. Water carrying dissolved minerals and sediment may seep into the empty space of a mold. If the water deposits the minerals and sediment there, the result is a cast. Molds and Casts 5

6 What are the different kinds of fossils? Carbon films An extremely thin coating of carbon on rock. HOW DOES A CARBON FILM FORM? When sediment buries an organism, some of the materials that make up the organism can become gases. These gases escape from the sediment, leaving carbon behind. Eventually, only a thin film of carbon remains. Like Carbon Copies of documents! Carbon Films What are the different kinds of fossils? Trace fossils Trace fossils provide evidence of the activities of ancient organisms. A fossilized footprint is on example of a trace fossil. Other examples of trace fossils include the trails that animals followed or the burrows that they lived in. 6

7 Trace Fossils What are the different kinds of fossils? Preserved Remains Some processes preserve the remains of organisms with little or no change. Some remains are preserved when organisms become trapped in tar. Ancient organisms also have been preserved in amber. Amber is the hardened resin, or sap, of evergreen trees. Freezing is another way in which remains can be preserved. Preserved Remains 7

8 Ice Cores: Another way scientists use to learn about Earth s past. A tube of ice that has been drilled from polar ice caps. Shows the layers of ice and snow built up over time. Tells scientists about past climates, temperatures, and atmospheric conditions in the past (ex: CO2) Sometimes preserved remains are found nearby! What do fossils tell us about organisms? The fossil record provides an explanation about the history of life on Earth. The fossil record that fossils occur in a particular order in some areas over the world. This infers that life on Earth has evolved, or changed. Thus, the fossil record provides evidence to support the theory of evolution. What do fossils tell us about organism? A scientific theory is a well tested concept that can try to explain a wide range of observations. Evolution is the gradual change in living things over long periods of time. (more another day) The fossil record shows that different types of organisms may have evolved. But many others have become extinct. A type of organism is extinct if it no longer exists and will never again live on Earth. 8

9 What do fossils tell about how organisms have changed over time? Paleontologists use fossils to build up a picture of Earth s environments in the past. Fossils also provide evidence of Earth s climate in the past. Scientists can use fossils to learn about changes in Earth s surface. In Summary Most fossils form when living things die and are quickly buried by sediment, which eventually hardens and preserves parts of the organisms. The major kinds of fossils include petrified remains, molds, casts, carbon films, trace fossils, and preserved remains. The fossil record shows that many different organisms have lived on Earth at different times and that groups of organisms have changed over time. Clues to the past Many fossils give us an idea of what life was like long ago Plants give clues about the diet of animals Animals give clues about the availability of plants and the climate when they lived Many clues fit together to make a more complete picture of what the world was like long ago 9

10 Can we ever really know? No matter how many clues we have, we can never really know what life was like long ago We can make an educated guess, and fill in the gaps using what we know about life today It s fun to imagine what it was like when the dinosaurs lived. Try it next time you feel bored! Fossils Preserved fossils Rock Fossils amber tar ice Trace fossils Casts and molds Petrified fossils Carbon films Movie time! ~10 min _DCP4cLVNg ( in folder!) 10

11 Some interesting fossil finds: dinosaur-fossil-mammal-stomach.html News/idCATRE72O4TZ How do these articles have an effect about what you researched regarding the Geologic Time Scale and the Fossil Record? Some interesting fossil finds: With the finding of soft tissue being preserved in ancient organisms, what are the explanations as to why they are indeed preserved? Why do you think there are fossil graveyards around the world? (your thoughts) Some interesting fossil finds: Based on your research on the geologic time scale, what are your thoughts about these living fossils identified in these articles: