Index Fossils

Index Fossils? After going through this module, you are expected to: 1. define what is index fossils or guide fossils and subdivisions of geologic time scale. 2. identify how index fossils are used to described subdivisions of geologic time scale. 3. explain why it is rare for an organism to be preserved as a fossil. 4. distinguish the difference between body fossils and trace fossils. 5. describe five types of fossilization and what a living fossil is. 6. value the importance of index fossils and give several examples. 7. explain how the fossil record shows us that species evolve over time. 8. describe the general development of Earth’s life forms over the last 540 million years Article about Index fossils. A fossil is the remain or evidence of a living thing. The most common fossils are bones, skills, teeth, leaves, spores, and seeds of pollen grains. Most fossils are formed when the whole part of an organism becomes buried in sedimentary rocks, which provide the most important evidence about the evolution of plants and animals. Fossils give clues about organisms that lived long ago. They also provide evidence about how Earth’s surface changed overtime. Fossils helps scientist understand what past environments may have been like. There are five main types of fossils namely: 1) Petrified fossils are formed through petrification that means turning into stones. It forms when minerals replace all part of an organism. 2) Molds and casts form when hard parts of an organism are buried in sediments such as sand, silt, or clay. A cast is formed as the result of mold. Minerals and sediments fill the mold’s empty spaces and make a cast. (3) Carbon Films, all living things contain an element called carbon. When an organism dies and is buried in sediments, the material that make up the organism break down. Eventually, only carbon remains. (4) Trace fossils show the activities of organism. An animal makes a footprint when it steps in sand or mud. Overtime the footprint is buried in layers of sediment, then sediment becomes solid rock. (5) Preserved remains, and some organisms get preserved in or close to their original states. There are insect, is organism, organism, some ways it can happen;(a) Amber-an organism, such as trapped in a tree’s sticky resins and dies. (b) Tar an such as mammoth, is trapped in a tar pit and dies. (c) Ice-an such as wooly mammoth, dies in very cold regions. Definition of terms: A fossil is any remains of ancient life. It can be body fossils which are remains of the organism itself, or trace fossils, such as burrows, tracks, or other evidence of activity. Preservation as a fossil is a relatively rare process. The chances of becoming a fossil are enhanced by quick burial and the presence of preservable hard parts, such as bones or shells. Fossils form in five ways: preservation of original remains, permineralization, molds and casts, replacement, and compression. Rock formations with exceptional fossils are called very important for scientists to study. They allow us to see information about organisms that we may not otherwise ever know. Index fossils are fossils that are widespread but only existed for a short period. Index fossils help scientists to find the relative age of a rock layer and match it up with other rock layers. Living fossils are organisms that haven’t changed much in millions of years and are still alive today. Fossils give clues about the history of life on Earth, environments, climate, movement of plates, and other events. Adaptations are favorable traits that organisms inherit. Adaptations develop from variations within a population and help organisms to survive in their given environment. Changes in populations accumulate over time; this is called evolution. The fossil record shows us that present-day life forms evolved from earlier different life forms. It shows us that the first organisms on Earth were simple bacteria that dominated the Earth for several billion years. Beginning about 540 million years ago more complex organisms developed on Earth. During the Phanerozoic Eon, all the plant and animal types we know today have evolved. Many types of organisms that once lived are now extinct. Earth’s overall environment, especially the climate, has changed many times, and organisms change too over time. Fossils Throughout human history, people have discovered fossils and wondered about the creatures that lived long ago. The griffin, a mythical creature with a lion’s body and an eagle’s head and wings, was probably based on skeletons of Protoceratops that were discovered by nomads in Central Asia. (Figure 1.1) Figure 1.1. Skeletons of Protoceratops Another fossil reminded the Greeks of the coiled horns of a ram. The Greeks named them ammonites after the ram god Ammon. Similarly, legends of the Cyclops may be based on fossilized elephant skulls found in Crete and other Mediterranean islands. Can you see why? (Figure 1.2) Figure 1.2. Ammonite (left) and elephant skull (right) The giant pterosaur Quetzalcoatlus had a wingspan of up to 12 meters (39 feet). The dinosaur Argentinosaurus had an estimated weight of 80,000 kg, equal to the weight of seven elephants! Other fossils, such as the trilobite and ammonite, impress us with their bizarre forms and delicate beauty.