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The History of Life. 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. Fossils. Evidence of an organism that lived long ago Paleontologists Study ancient life Uses fossils to:

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history of the earth
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
  • 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
how fossils form
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
types of fossils
Types of Fossils
  • Trace fossils
    • An indirect evidence left by an animal
    • Include a footprint, a trail, or a burrow
    • A replica or cast
    • Minerals in rocks fill a space left by a decayed organism
    • An empty space left by an organisms after it decays
    • Minerals penetrate and replace the hard parts of an organism
  • Permineralized
    • Void spaces in original organism is filled by minerals



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

Amber preserved


dating fossils
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
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
    • the time it takes a radioactive element to get to half its original amount
    • Potassium 40 - 1.3 billion yrs
    • Carbon 14 - 5730 years
geologic time scale
Geologic Time Scale
  • a type of calendar based on the different types of living organisms that have appeared on Earth
precambrian era
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

paleozoic era
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
mesozoic era
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
theory of continental drift
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
the early ideas
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
francesco redi
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
louis pasteur
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
  • All living things come from other living things
  • Became cornerstone of biology after Pasteur’s experiment
the modern ideas
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
Stanley Miller and Harold Urey
  • Used Oparin’s hypothesis to setup experiment
  • Produced amino acids and other organic compounds
formation of protocells
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
the first true cells
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
Photosynthesizing prokaryotes
    • Increased oxygen in atmosphere
  • Eukaryotes evolved from prokaryotes
endosymbiont theory
Endosymbiont Theory
  • Eukaryote provided beneficial environment
  • Prokaryote provided method of energy synthesis
  • Endosymbiotic, aerobic prokaryotes evolved into modern mitochondria
  • Photosynthetic cyanobacteria evolved into chloroplasts