Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Welcome to Class How do we determine the age of something? Agenda • Radioactive Decay Lab • Fossils Movie • Fossils Notes Radioactive Decay Lab Movie • Fill out the worksheet as you watch the movie • I will be collecting these FOSSILS • fossils - trace or remains of organisms that lived long ago – discovered in sedimentary rock • paleontology - scientific study of fossils • Help find relative and absolute ages of rocks Interpreting the Fossil Record • Fossil Record – provides evidence about the history of life on Earth – Shows how organisms have changed over time • Provide clues to past geologic events, climates, and the evolution of living things over time – see how environmental changes affected living organisms Interpreting the Fossil Record • What do these giant fossilized oysters tell us? Fossilization • Dead organisms buried quickly or protected from decay become fossils • Generally only the hard parts become fossils – Rarely an entire organism may be preserved • Sometimes only a replica of the original organism remains – Others provide evidence that life once existed Mummification • Mummified remains are found in very dry places – most decay causing bacteria cannot survive in these places • Some ancient civilizations mummified their dead – extracted internal organs and wrapped the body in strips of cloth Amber • Insects get trapped in the sap and are preserved when the sap hardens – Hardened tree sap is called amber • Delicate features (legs/antennae/DNA) can be preserved Tar Seeps • When thick petroleum comes to Earth’s surface, it forms a tar seep – covered by water – Animals become trapped and preserved in the tar Freezing • The low temperatures of frozen soil and ice can protect and preserve organisms – Most bacteria cannot survive freezing temps., organisms buried in frozen soil or ice do not decay Petrification • Mineral solutions (groundwater) replace original organic materials • Some common petrifying minerals are silica, calcite, and pyrite. • The substitution often results in the formation of a nearly perfect mineral replica of the original organism Types of Fossils Using a book, look up types of fossils Include: – trace fossils – imprints – molds and casts – Coprolites – Gastroliths Types of Fossils • trace fossil - a fossilized mark that formed by the movement of an animal on or in soft sediment • No part of the original organism survives in fossil form – fossilized evidence of past animal movement – provide information about prehistoric life • A trace fossils in an important clue to the animal’s appearance and activities. Imprints • Carbonized imprints of leaves, stems, flowers, and fish made in soft mud or clay • When original organic material partially decays, it leaves behind a carbon-rich film – An imprint displays the surface features of the organism Molds and Casts • After a shell is buried, it decays and leaves an empty space called a mold – sand or mud fills a mold and hardens forming a cast • A cast is a replica of the original organism Coprolites • coprolites - fossilized dung or waste materials from animals • They can be cut into thin sections and observed through a microscope. – See the feeding habits of animals, such as dinosaurs Gastroliths • Some dinosaurs had stones in their stomachs to help grind their food – these stones, called gastroliths, survive as fossils • Gastroliths are recognized by smooth, polished surfaces and their close proximity to dinosaurs remains Index Fossils • Index fossil - a fossil used to establish age of rock layers – distinct, abundant, widespread – existed for only a short span of geologic time • Help determine relative and absolute ages of rock layers Index Fossils and Absolute Age • Scientists can use index fossils to estimate absolute ages of specific rock layers • Lived during short spans of geologic time, the layer where an index fossil was discovered can be dated accurately • Scientists can also use index fossils to date rock layers in separate area