welcome to class how do we determine the age of something?
TRANSCRIPT
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Welcome to Class
How do we determine the age of something?
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Agenda
• Radioactive Decay Lab
• Fossils Movie
• Fossils Notes
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Radioactive Decay Lab
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Movie
• Fill out the worksheet as you watch the movie
• I will be collecting these
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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
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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
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Interpreting the Fossil Record
• What do these giant fossilized oysters tell us?
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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
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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
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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
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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
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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
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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
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Types of Fossils
Using a book, look up types of fossils
Include:– trace fossils– imprints– molds and casts– Coprolites– Gastroliths
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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.
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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
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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
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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
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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
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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
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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