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The History of Life

Uncover Earth's ancient past through fossils and rocks, tracing the history of life from 3.9 billion years ago. Learn about paleontology, fossil dating methods, and the geologic time scale. Discover the origins of life and cells, revealing the fascinating journey of evolution over billions of years.

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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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