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The History of Life

Delve into the fossil record to infer past life, behavior, environments, and diet. Understand how fossils are formed, dated, and interpreted. Learn about radioactive dating and the geologic time scale. Explore the evolution of organisms through time.

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The History of Life

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  1. The History of Life The Fossil Record

  2. Fossils & Ancient Life • Paleontologists • Scientists Who Study Fossils • Infer What Past Life • Looked Like • What They Ate & What Ate Them • Behavior • Environment They Lived In

  3. What They Looked Like

  4. What They Ate

  5. Behavior & Environment 3.6 MYA

  6. Fossils & Ancient Life • Fossil Record • Organization Of Fossils From Oldest To Newest Including Supporting Information Of Other Life Forms In Their Environment

  7. Fossils & Ancient Life Key Concept The Fossil Record Provides Evidence About The History Of Life On Earth. It Also Shows How Different Groups of Organisms Have Changed Over Time.

  8. Fossils & Ancient Life • Each Fossil Is Found Only In It’s Particular Time Period or Layer • A Kind Of Fossil Clock • Of All The Life Forms That Have Ever Lived On Earth ----- • 99% Are Extinct • No Longer Alive

  9. How Fossils Are Formed • Most Form In Sedimentary Rock • Plants & Animals Die In A Water Environment And Are Covered With Silt • Others Covered With Fine Sand or Volcanic Ash • Compressed Into Rock

  10. How Fossils Are Formed • Organic Materials Are Replaced By Minerals • Quality Of Preservation Varies • Fossils Include: • Bones • Eggs • Footprints • Skin Impressions, etc.

  11. Interpreting Fossil Evidence • Fossils Are Released By • Tectonic Forces • Erosion • Mining • Construction

  12. Interpreting Fossil Evidence • Most Fossils Disarticulated • Predation • Scavengers • Rot • Catastrophic Events May Bury & Preserve Whole Animals and/or Ecosystems

  13. Life On Earth

  14. Dating Fossils Two Types of Dating • Relative Dating Organizes Fossils By Order (1st, 2nd, 3rd, etc.) Tells You Which Organisms Lived In What Order Does Not Give You Actual Years • Absolute Dating Gives You Age In Years Before Present e.g. 150 Million Years Ago

  15. Relative Dating

  16. Relative Dating

  17. Relative Dating • The Age of a Fossil Is Determined By Comparing Its Placement With Other Fossils In Other Layers Of Sedimentary Rock • Allows Comparison Of Layers World Wide

  18. Relative Dating • Index Fossils • Easily Recognized • Existed For A Short (?) Period • Wide Geographic Distribution • Does Not Give Absolute Age

  19. Relative Dating Key Concept: Relative Dating Allows Paleontologists To Estimate A Fossils Age Compared With That Of Other Fossils

  20. Radioactive Dating Uses The Half Lives Of Certain Radioactive Isotopes In Igneous Rocks To Calculate The Age Of A Fossil Half Life The Length Of Time Required For Half Of The Radioactive Atoms In A Sample To Decay

  21. Radioactive Dating Key Concept: In Radioactive Dating, Scientists Calculate The Age Of A Sample Based On The Amount Of Remaining Radioactive Isotopes It Contains

  22. Radioactive Dating Different Radioactive Elements Have Different “tick rates” Carbon-14 Half-life = 5,730 years Decays to Nitrogen-14 Useful Back 60,000 years

  23. Absolute Age Radioactive Dating

  24. Geologic Time Scale Developed By Paleontologists To Classify Geologic And Biologic Events Rock Layers Fossils Present

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