The History of Life

1. The History of Life

2. History of the Earth • Formed 4.6 billion year ago • Started as hot ball of rock • Earth cooled 4.4 bya • First life began between 3.9 and 3.4 bya

3. Fossils • Evidence of an organism that lived long ago • Paleontologists • Study ancient life • Uses fossils to: • understand events that happened long ago • Determine the kinds of organisms that lived during the past and their behaviors • Study ancient climate and geography

4. How fossils form • Organisms are buried in mud, sand, or clay • Sediments cover the organism, slows decomposition • Minerals from sediments seep into body • Over time, sedimentary layers compressed into rock • Mineral replace the body’s bone material • Earth’s movement or erosion expose the body • Rocks form at relatively low temperatures and pressure • Prevent damage of organism

5. Types of Fossils • Trace fossils • An indirect evidence left by an animal • Include a footprint, a trail, or a burrow

6. Casts • A replica or cast • Minerals in rocks fill a space left by a decayed organism

7. Molds • An empty space left by an organisms after it decays

8. Petrified • Minerals penetrate and replace the hard parts of an organism • Permineralized • Void spaces in original organism is filled by minerals Petrified Permineralized

9. Amber-preserved or frozen • An entire organism quickly trapped in ice or tree sap and hardens Amber preserved Frozen

10. Dating fossils • Relative dating • uses the position of fossils in sediment layers • oldest fossil at the bottom layer, youngest on top • Can only determine whether one fossil is older than another • Cannot determine the actual age

11. Radiometric dating • use radioactive isotopes (atoms with unstable nuclei that break down or decay) • decay of each radioactive element is known and continues at a steady rate

12. Half-life • the time it takes a radioactive element to get to half its original amount • Potassium 40 - 1.3 billion yrs • Carbon 14 - 5730 years

13. Geologic Time Scale • a type of calendar based on the different types of living organisms that have appeared on Earth

14. Precambrian Era • Starts 4.7 bya • Accounts for 87% of Earth’s history • Oldest rock dates 3.4 bya • Unicellular prokaryotes appeared • Eukaryotes appeared 2.1 bya • Ended 345 mya Oldest rock from Yukon, 4 byo

15. Paleozoic Era • 345 to 248 mya • Appearance of plants and animals including fishes, reptiles, amphibians and ferns • 90% of Earth’s marine species and 70% of land species disappeared

16. Mesozoic Era • 248 to 65 mya • Triassic • Oldest • Mammals appeared • Dinosaurs first appeared • Jurassic • Age of dinosaurs • Cretaceous • Mammals and flowering plants • Dinosaurs and 2/3 of living species became extinct

17. Theory of Continental Drift • Continents were joined in a landmass known as Pangaea • Pangaea broke apart resulting in two large masses • At the end of the Mesozoic, most of the continents had taken on their modern shapes • Explained by plate tectonics • Movement of the continents

19. The Origin of Life

20. The Early Ideas • Spontaneous generation • Nonliving material can produce life • Experiments to disprove this theory • Francesco Redi • Used maggots in covered and uncovered jars • Louis Pasteur • Used curved flasks with heated broth

21. Francesco Redi • 1668 • Showed that rotting meat kept away from flies would not produce new flies • Maggots appeared only on meat that had been exposed to flies • Eggs laid on meat

22. Louis Pasteur • Mid- 1800s • Used curve-necked flasks • Microorganisms were prevented from entering the flask • When curved necks were broken, broth became cloudy with microorganims

23. Biogenesis • All living things come from other living things • Became cornerstone of biology after Pasteur’s experiment

24. The Modern Ideas • Alexander Oparin • Life began in the oceans that formed on early Earth • Energy from sun + lightning+ Earth’s heat = simple compounds (eg. amino acids) • Earth cooled, water vapor condensed to form lakes and seas, compounds collected in the water

25. Stanley Miller and Harold Urey • Used Oparin’s hypothesis to setup experiment • Produced amino acids and other organic compounds

26. Formation of Protocells • Sidney Fox • Produced protocells • Large, ordered structure, enclosed by a membrane • Carries out some life activities (growth and division) • Heated amino acids

27. The First True Cells • Prokaryotes evolved from a protocell • Heterotrophs • Anaerobic • Archaebacteria • Prokaryotic • Autotrophs • Made glucose by chemosynthesis • Lived in harsh environments • Deep-sea vents and hot springs

28. Photosynthesizing prokaryotes • Increased oxygen in atmosphere • Eukaryotes evolved from prokaryotes

29. Endosymbiont Theory • Eukaryote provided beneficial environment • Prokaryote provided method of energy synthesis • Endosymbiotic, aerobic prokaryotes evolved into modern mitochondria • Photosynthetic cyanobacteria evolved into chloroplasts