Fossils & Geologic Time

1. Fossils & Geologic Time Mrs. Wisher WRITE EVERYTHING IN YELLOW!!

2. 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

3. 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

4. Relative Dating

5. Preserved Remains • Real parts of real organisms that have not changed • Wooly Mammoth in ice or tar • Insects in amber • Mummified remains

6. 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.

8. QUESTIONS • Students at “B” seats – close your notebook and teach your table the difference between relative and absolute dating.

9. 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.

10. Molds & Casts • Mold – an impression of the organism • Cast – an object formed when a mold is filled with sediment

11. 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.

12. 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?

13. Precambrian Era • Early bacteria and algae form • First sedimentary rocks appear • First multicellular organisms develop late in Precambrian.

14. Phanerozoic Eon – “visible life” • 1. Paleozoic Era (old life) • 2. Mesozoic Era (middle life) • 3. Cenozoic Era (recent life)

15. 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.

16. 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

17. 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

18. 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

19. 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.

20. Cenozoic Era Early animals could be much different than their modern versions. Early horses were much smaller and had toes.

21. Questions? • Discuss with your shoulder partner, why do you believe that each of the Era’s ended at the time frame that they ended.

22. 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.

23. 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

24. Homo Neanderthalensis

25. Otzi the Iceman