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The History of Life

The History of Life. Ch 14. Earth’s Early History. Evolution is a scientific THEORY based on different types of evidence collected over the years Evidence Includes: Earth was an inhospitable planet Hot Volcanic gasses First organisms appeared between 3.5 to 3.9 billion years ago

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The History of Life

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  1. The History of Life Ch 14

  2. Earth’s Early History Evolution is a scientific THEORY based on different types of evidence collected over the years Evidence Includes: • Earth was an inhospitable planet • Hot • Volcanic gasses • First organisms appeared between 3.5 to 3.9 billion years ago There is direct evidence of Earth’s history • Fossils & rocks show that Earth formed about 3.9 billion years ago

  3. History in Rocks Fossils = any evidence of an organism that lived long ago • Trace fossils–something left by an animal (example footprint, trail, burrow) • Casts– minerals in rocks fill a space left by a decayed organism (form a replica of organism) • Petrified fossils – minerals replace the hard parts of an organism • Imprints– thin objects can leave an imprint as sediments turn to rocks • Amber-preserved & frozen – actual organism is trapped in amber or ice

  4. Dunkleosteus (30 ft long; bony skull shown here is about 1 meter high) Extinct at the end of the Devonian

  5. Fossil examples

  6. Studying fossils • Paleontologists study fossils • Kinds of organisms that lived • Learn about behavior • Earth’s climate • Geography (rivers, continent position) • Fossils are found in sedimentary rock • Organism is buried in mud, sand, or clay soon after death • Particles compress & harden over time to form sedimentary rock

  7. Determining Fossil Age Relative dating • Surface layers are newest so they have the most recent fossils. • Deeper layers contain older fossils • Scientists can determine the order of appearance & extinction Radiometric dating • Uses radioactive isotopes • Potassium 40 (half life of 1.3 billion yrs) • Carbon 14 (half life of 5730 years) • Scientists can approximate ages

  8. The Geologic Time Scale • A time scale of Earth’s existence based on fossil evidence • 4.6 billion years ago – present • Divided into Eras • Precambrian, Paleozoic, Mesozoic, Cenozoic • Distinguished by organisms that lived during the era • Eras are divided into periods • Mass extinction = entire groups of organisms disappear from the fossil record almost all at once

  9. Precambrian Era • 87% of Earth’s history • 3.5 billion years ago to 544 million years ago • Began with prokaryotes • Eukaryotes developed and flourished • Soft-bodied invertebrates (jellyfish, sponges) • Oldest fossils – 3.5 billion years old • resemble forms of modern species of cyanobacteria • Stromatolites – evidence of photosynthetic bacteria

  10. Paleozoic Era • Beginning(Cambrian period) • Dramatic increase in diversity of life forms • Worms, sea stars, trilobitesin the oceans • Fish appeared – oldest animals with backbones • Land species – ferns & seed plants • Middle – amphibians • End – Reptiles • Largest mass extinction – 90% of Earth’s marine species & 70% of the land species disappeared

  11. Mesozoic Era • Began about 245 million yrs ago • Triassic • Mammals appeared on Earth • Early mammals were small and mouse-like • Jurassic(began ~ 280 million years ago) • Age of the Dinosaurs • Birds appeared • Evidence of bird relation to dinosaurs • Cretaceous(began ~ 144 million years ago) • New types of mammals & flowering plants • Mass extinction of dinosaurs ~ 66 million years ago

  12. Geological Events of the Mesozoic • Geologic evidence of a large crater East of Mexico • Could have filled the atmosphere with dust, changing climate • Continental Drift • Pangaea broke apart & continents began to move apart • Plate tectonics = Earth’s crust consists of several rigid plates on top of molten rock. • Plates continuously move • Explains continental drift

  13. Cenozoic Era • Began ~ 66 million years ago – the current era • Mammals began to flourish • Primates appeared(~30 million years ago) • Modern humans appeared (~200,000 yrs ago)

  14. 14.2 Origin of Life

  15. The Origin of Life on Earth • Abiogenesis – life from non-living things and Spontaneous Generation = idea that nonliving material can produce life • Disproven by Redi and Pasteur • Primordial Soup – natural processes formed early organic compounds • Miller-Urey experiment • Biogenesis = living organisms only come from other living organisms

  16. Redi & Pasteur

  17. The Origin of Cells • Prokaryotes – Archaebacteria (1st cells) • Eukaryotes – endosymbiont hypothesis • Separate DNA in chloroplasts and mitochondria • Both organelles the same size and shape of bacteria

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