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The Fossil Record: Dating and Understanding the History of Life

Explore the fossil record and learn how fossils are formed, how they can be dated, and what they tell us about the history of life on Earth. Discover the geologic time scale and the major changes in organisms over time.

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The Fossil Record: Dating and Understanding the History of Life

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  1. Chapter 19: The History of Life

  2. 19–1 The Fossil Record A. The Fossil Record B. How Fossils Form C. Dating Fossils • Relative Dating • Radioactive Dating D. Geologic Time Scale • Eras (Paleozoic, Mesozoic, Cenozoic) • Periods

  3. The Fossil Record • Provides evidence about history of life on Earth • Shows how different groups of organisms change over time • More than 99% of all species that have ever lived on Earth have become extinct. Archaeopteryx

  4. How Fossils Form • How Fossils Form: Active Art http://www.phschool.com/webcodes10/index.cfm?fuseaction=home.gotoWebCode&wcprefix=cbe&wcsuffix=5171 • Lucy’s fossil: http://www.pbs.org/wgbh/evolution/library/04/3/l_043_01.html Dead organisms are buried by layers of sediment, which forms new rock. The preserved remains may later be discovered and studied. Water carries small rock particles to lakes and seas.

  5. Dating Fossils • Relative Dating • Radioactive Dating How old is this Archaeopteryx fossil? 150 million years old

  6. Relative Dating • estimate age of a fossil by comparing to other fossils • oldest fossils are usually in deepest layers • index fossils (trilobites) used to compare the ages of rocks and other fossils • cannot determine exact numerical age

  7. Radioactive (“absolute”) Dating • calculate numerical age of a sample based on amount of radioactive isotopes • Half-life = length of time required for half of the radioactive atoms to decay • Carbon-14 half-life = 5770 yrs. used to date younger fossils • Potassium-40 half-life = 1.26 billion yrs. used to date older fossils • http://www.pbs.org/wgbh/evolution/library/03/3/l_033_01.html

  8. Age of fossil with respect to another rock or fossil (that is, older or younger) Age of a fossil in years Comparing depth of a fossil’s source stratum to the position of a reference fossil or rock Determining the relative amounts of a radioactive isotope and nonradioactive isotope in a specimen Imprecision and limitations of age data Difficulty of radioassay laboratory methods Relative vs. Radioactive Dating Comparing Relative and Radioactive Dating of Fossils Relative Dating Radioactive Dating Can determine Is performed by Drawbacks

  9. Geologic Time Scale • represents evolutionary time • major changes in animal/plant fossils at specific rock layers divided geologic time according to major fossil changes

  10. Geologic Time Scale Geologic Time Scale First life = 4mya

  11. 19–2 Earth’s Early History A. Formation of Earth B. The First Organic Molecules (Miller & Urey) C. How Did Life Begin? • Formation of Microspheres • Evolution of RNA and DNA D. Free Oxygen E. Origin of Eukaryotic Cells F. Sexual Reproduction and Multicellularity

  12. Formation of the Earth • Earth formed about 4.6 billion years ago. • Early earth’s atmosphere contained: • Hydrogen cyanide, carbon dioxide, carbon monoxide, nitrogen, hydrogen sulfide, and water vapor. • Little or no oxygen • Hot! No oceans or liquid water, just water vapor in air. Early earth Approx. 4 billion years ago

  13. Mixture of gases simulating atmospheres of early Earth Spark simulating lightning storms Cold water cools chamber, causing droplets to form Condensation chamber Water vapor Liquid containing amino acids and other organic compounds Miller-Urey Experiment • What were the first organic molecules on earth? • (1950’s) Miller & Urey made amino acids by passing sparks through a mixture of hydrogen, methane, ammonia, and water vapor. • (1995) one of Miller’s experiments produced cytosine & uracil (found in RNA) • experiments suggest how simple compounds found could combine to form organic compounds needed for life

  14. How Did Life Begin? • Under certain conditions, large organic molecules can sometimes form tiny bubbles called proteinoid microspheres. • These are NOT cells, but have some of the characteristics of living things. • Selectively permeable membrane • Can store and release energy

  15. Free Oxygen • No oxygen in early Earth’s atmosphere. (3.5 bya) • Ancient photosynthetic organisms (cyanobacteria) produced a rise in oxygen in the Earth’s atmosphere (2.2 bya) • Cyanobacteria produce stromatolite formation in the ocean

  16. Endosymbiotic Theory Chloroplast Eukaryotic cells arose from living communities formed by prokaryotic organisms. Plants and plantlike protists Aerobic bacteria Ancient Prokaryotes Photosynthetic bacteria Nuclear envelope evolving Mitochondrion Primitive Photosynthetic Eukaryote Animals, fungi, and non-plantlike protists Primitive Aerobic Eukaryote Ancient Anaerobic Prokaryote Endosymbiotic Theory Video The Evolution of Cells

  17. Sexual Reproduction & Multicellularity • Eukaryotic cells began to reproduce sexually, producing more genetic variation, leading to evolution of multicellular organisms. Ancient jellyfish fossil multicellular organism

  18. Evolution of Life Concept Map Evolution of Life Concept Map Evolution of Life Early Earth was hot; atmosphere contained poisonous gases. Earth cooled and oceans condensed. Simple organic molecules may have formed in the oceans.. Small sequences of RNA may have formed and replicated. First prokaryotes may have formed when RNA or DNA was enclosed in microspheres. Later prokaryotes were photosynthetic and produced oxygen. An oxygenated atmosphere capped by the ozone layer protected Earth. First eukaryotes may have been communities of prokaryotes. Multicellular eukaryotes evolved. Sexual reproduction increased genetic variability, hastening evolution.

  19. Geologic Time Websites • Go to Biology Page Website. • Click on Unit 5 Evolution • Look under WebLinks column. • Explore the following websites: • Geologic Time • A Brief History of Life

  20. 19–4 Patterns of Evolution Macroevolution: large scale evolutionary patterns that occur over long periods of time. The six types are: • Extinction • Adaptive Radiation • Convergent Evolution • Coevolution • Punctuated Equilibrium • Developmental Genes and Body Plans

  21. Extinction • More than 99% of all species that have ever lived are now extinct. • Mass extinctions lead to bursts of evolution that produce many new species. • Ex. the extinction of the dinosaurs cleared the way for the evolution of mammals and birds. • http://www.pbs.org/wgbh/evolution/library/03/2/l_032_02.html • http://www.pbs.org/wgbh/evolution/extinction/index.html K-T event (65 mya) 70% of species died in a mass extinction

  22. Adaptive Radiation • Example = Birds on the Hawaiian islands evolved from a common ancestor over millions of years. • The birds that survived were most adapted to their environment. Birds on Hawaiian Islands

  23. Convergent Evolution • Unrelated organisms resemble one another. • Ex. all organisms above have wings, adapted for flying, however they evolved from different ancestors.

  24. Coevolution • Two species evolve in response to changes in each other over time. • Ex. hawk moth evolved and has long feeding tube to suck nectar from orchid Plants and pollinators co-evolve

  25. Punctuated Equillibrium • Long, stable periods interrupted by brief periods of more rapid change. • Ex. peppered moths evolved rapidly after industrial revolution.

  26. Developmental Genes & Body Plans • All animals have master control genes that code for the a basic body plan. • Mutations cause variations in those body plans. • http://www.pbs.org/wgbh/evolution/library/03/4/l_034_04.html

  27. Unrelated Related Intense environmental pressure Similar environments Inter-relationshiops Small populations Different environments Convergent evolution Punctuated equilibrium Adaptive radiation Coevolution Extinction Macroevolution Flowchart Species that are form in under under in in can undergo can undergo can undergo can undergo can undergo

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