Index Fossils and Geologic Time “The Past is the Key to the Present”
Fossils & Geologic Time
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Transcript of Fossils & Geologic Time
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Fossils & Geologic Time
Mrs. Wisher
WRITE EVERYTHING IN YELLOW!!
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What Are Fossils?
• Fossils are formed when living things die and are trapped in sediments and become rocks
• Petrified fossils are where minerals replace all or part of an organism
• Trace fossils provide evidence of the activities of organisms
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Dating Fossils
• Relative age dating – compares their age to age of other rocks
• Absolute age dating – tells their age in years by looking at the decay of isotopes
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Relative Dating
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Preserved Remains
• Real parts of real organisms that have not changed– Wooly Mammoth
in ice or tar– Insects in amber– Mummified
remains
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Preserved Remains
• Long before white men came, Indians knew of and worked in Mammoth Cave in KY. In 1935 two guides exploring found a mummy high on a ledge. From its position and the articles found with it, archeologists pieced together the story. An Indian miner was digging for something in sand on the ledge. A rock above slipped and pinned him down. The body, found many centuries later in an excellent state of preservation, was clad in a breech clout, woven of fiber. Crude stone implements lay nearby.. Close by bundles of reeds, thrust into the sand with singed ends indicated he was using them as a torch. The mummy was found three miles from the nearest natural entrance—three miles of pitch black darkness, lighted for that long-ago miner only by the reed torches he carried. Today the mummy rests in an air-tight glass case just below the ledge on which it was found.
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QUESTIONS
• Students at “B” seats – close your notebook and teach your table the difference between relative and absolute dating.
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QUESTIONS
• Students at “B” seats – close your notebook and teach your table the difference between relative and absolute dating.
• Relative dating is using the position of the rock layers to determine which is youngest or oldest. Absolute dating gives you a time frame of age based on radioactive decay.
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Molds & Casts
• Mold – an impression of the organism
• Cast – an object formed when a mold is filled with sediment
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Geological Time Scale
• Why use geological time?
• Earth is about 4.6 billion years old
• Modern humans have only been here less than 100,000 years or less than 1% of Earth’s history.
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Geologic Time Scale
– Eras – geological history is divided into 4 eras– Periods – each era is divided into periods
• What 3 periods make up the Mesozoic era?
– Epochs – each period is subdivided into an epoch
• Only the Cenozoic (or most recent) era is divided into epochs. Can you think of why?
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Precambrian Era
• Early bacteria and algae form
• First sedimentary rocks appear
• First multicellular organisms develop late in Precambrian.
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Phanerozoic Eon – “visible life”
• 1. Paleozoic Era (old life)
• 2. Mesozoic Era (middle life)
• 3. Cenozoic Era (recent life)
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Paleozoic Era
• 570 mya to 225 mya
• Trilobites were common animals
• Life explodes during the Paleozoic
• Land plants appeared in middle Paleozoic.
• “Age of the Fish”, all animal life is in the sea - sharks, rays, and bony fish existed.
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Paleozoic Era
• Tropical jungle like forest were prevalent by the end of the era.
• Insects (some huge) were the predominant animals.
• Reptiles evolved during the late Carboniferous period
• A mass extinction at the end of the Paleozoic wiped out 95% of all life
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Mesozoic Era
• 225 mya – 65 mya• “Age of the Reptiles”• Dinosaurs roamed
Earth.• Pangaea breaks up
during the Jurassic period and is in the present position by the late Cretaceous period
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Mesozoic Era
• Birds and mammals started evolving during the last part of the Mesozoic.
• Widespread volcanic activity occurs
• Mass extinction at the K-T boundary is supported by the fossil record
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Cenozoic Era
• Recent Life (65 mya to present)• Divided into the Tertiary & Quaternary
period• “Age of mammals”• Ice Age began 3 mya (on New Year’s Eve.)• Took 75000 years to form, stayed 10000
years, then retreated.
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Cenozoic Era
• Early animals could be much different than their modern versions.
• Early horses were much smaller and had toes.
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Questions?
• Discuss with your shoulder partner, why do you believe that each of the Era’s ended at the time frame that they ended.
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Questions?
• Discuss with your shoulder partner, why do you believe that each of the Era’s ended at the time frame that they ended.
• Each of the Era’s (except the Cenozoic which we are still in) ended with a mass extinction event.
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Age of Man
• Man evolved at 10:30 pm on New Year’s Eve.• Hominids evolved during the Quaternary period• Australopithecus, the earliest ancestor, evolved
around 3 million years ago• Early hominids include Homo erectus, habilis, and
neanderthalensis• Homo Sapian sapian is the modern man
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Homo Neanderthalensis
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Otzi the Iceman
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