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Fossil Record and Ancient Life: Discovering Extinct Species

Learn about the fascinating world of fossils and how they can reveal information about extinct species. Explore the various types of fossils, how they form in sedimentary rock, and the methods used to date them. Discover the geological forces and biological processes that have shaped Earth's history and the organisms that inhabit it.

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Fossil Record and Ancient Life: Discovering Extinct Species

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  1. Chapter 19 Section 19-1: The Fossil Record

  2. Fossils and Ancient Life • Tell us about extinct species • Vary in size, type, degree of preservation • Only form under certain conditions • Incomplete

  3. Types of Fossils • As large as entirely preserved animal, with skin, hair, scales, or feathers • As small as bacteria, developing embryos, pollen grains • Fragments – teeth, bone pieces, bits of leaves • Traces – footprint, burrows, tracks, droppings • Mostly form in sedimentary rock, some in amber

  4. Fossils in Sedimentary Rock • Form when small particles of sand, silt, clay, or lime mud settle to the bottom of a body of water • Sediments bury dead organisms that have sunk to the bottom

  5. Fossils in Sedimentary Rock • Sediments continue to build up and over many years water pressure compresses lower segments, turning them to rock • Soft body structures decay quickly, usually only hard parts like wood, shells, teeth, bone remain • If the organism is buried quickly, it is protected from aerobic decay and leaves imprints

  6. What Fossils Can Reveal • Paleontologists (study fossils to learn about ancient life) compare body structures to living organisms, infer evolutionary relationships • Bone structure/trace fossils show how animals moved • Plant leaves/pollen suggest environment • Info compiled can recreate ecosystems

  7. Relative Dating • Places rock layers and their fossils into temporal sequence – lower layers are older • Index fossils are distinctive fossils used to establish and compare the relative ages of rock layers and the fossils they contain • Same index fossil found in 2 widely separated rock layers, the rock layers similar in age

  8. Relative Dating • Good index fossil species must be easily recognized, occur in only a few rock layers • Layers will be found in many places • Trilobites

  9. Radiometric Dating • Relies on radioactive isotopes which decay into nonradioactive isotopes at a steady rate • Compares amounts of radioactive isotopes in samples to determine precise age • Half-life : The time required for ½ the radioactive atoms in a sample to decay • Different half-lives for different elements

  10. Radiometric Dating • Carbon-14 has a short half-life (5730 years) and is commonly used to date young fossils • Fossils as old as 60,000 years • Naturally found in atmosphere, all living things • Decays to nitrogen-14 • Compare C-14 in fossil with C-14 in air • Older fossils dated by dating rock layers • Potassium-40: half-life 1.26 billion years • Uranium-238: half-life 4.5 billion years

  11. Geologic Time Scale • Timeline of Earth’s history • Basic divisions are eons, eras, periods

  12. Establishing the Time Scale • Studied rock layers, index fossils, to organize things by relative age • Noticed patterns/changes at boundaries between certain layers, used these to determine divisions • Later, radiometric dating used to assign specific ages • No regular pattern

  13. Naming the Divisions • Naming started before anything older than the Cambrian Period identified • Called everything before Precambrian time

  14. Precambrian Time • Actually 90% of Earth’s history

  15. Life on a Changing Planet • Earth/climate always changing, organisms evolved to new conditions • Global “heat wave” in Mesozoic Era temps 6-12 ° C higher than today • Ice Ages temps were 5° C cooler • Geological forces produced mountain ranges, moved continents • Volcanoes, local climates

  16. Plate Tectonics • Solid continental plates move slowly over Earth’s molten core • Continental drift • Continents collided to form supercontinents, then split apart and reformed

  17. Plate Tectonics • Mountain ranges rise where landmasses collide • Continents change position causing major ocean currents change course • Changes affect local and global climate

  18. Geological Cycles and Events • Affects distribution of fossils and living organisms • Fossils of Mesosaurus, a semiaquatic reptile, have been found in both South America and Africa

  19. Physical Forces • Evidence indicates that over millions of years, giant asteroids have crashed into Earth • Toss up so much dust, possibly blocking out sunlight and causing global cooling • Could have contributed to or caused worldwide extinctions

  20. Biological Forces • Earth’s early oceans contained large amounts of soluble iron and little oxygen. • During the Proterozoic Eon, photosynthetic organisms produced oxygen gas, removed carbon dioxide from the atmosphere • Reduced the greenhouse effect, cooled the globe • Organisms today shape the landscape by building soil from rock, and sand and cycle nutrients through the biosphere

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