History of Life on Earth

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Siobhan
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147156
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History of Life on Earth
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2012-04-11 23:52:12
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History Life Earth
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History of Life on Earth
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  1. The First Eukaryotes
    • 2.1 billion years ago
    • endosymbiont theory- one celll engulfed cyanobcteria and then it evolved as a symbiotic relationship
    • Key evidence :
    • Inner membranes are similar to plasma membranes of prokaryotes
    • Division is similar in these organelles and some prokaryotes
    • These organelles transcribe and translate their own DNA
    • Their ribosomes are more similar to prokaryotic than eukaryotic ribosomes

  2. Spontaneous generation
    • Spontaneous generation is the proposal that living organisms can arise from nonliving matter
    • Medieval beliefs reflected the concept of spontaneous generation
    • Maggots were thought to arise from meat
    • Microbes were thought to arise from broth
    • Mice were thought to arise from mixtures of sweaty shirts and wheat

  3. Conditions on early Earth made the origin of life possible


    • 1. Abiotic synthesis of small organic molecules
    • 2. Joining of these small molecules into macromolecules
    • 3. Packaging of molecules into protocells
    • 4. Origin of self-replicating molecules
  4. Oparin and Haldane
    • 1920s, Oparin and Haldane: early atmosphere was a reducing environment
  5. Miller and Urey
    • 1920s, Oparin and Haldane: early atmosphere was a reducing environment
    • 1953, Miller and Urey: abiotic synthesis of organic molecules in a reducing atmosphere is possible

  6. Protocells
    • Replication and metabolism are key properties of life
    • Protocells may have been fluid-filled vesicles with a membrane-like structure
    • lipids and other organic molecules can spontaneously form vesicles
    • Adding clay can increase the rate of vesicle formation


  7. Self-Replicating RNA and the Dawn of Natural Selection
    • The first genetic material was probably RNA, not DNA
    • ribozymes catalyze many different reactions
    • The early genetic material might have formed an RNA world
    • RNA are single stranded- can form many different shapes


  8. Figure 25.7 Clock analogy for some key events in Earths history.
    • Archeans- oldest. Formed prokaryotes. Then photosynthesizing prokaryotes (no membrane or nucleus) introduced oxygen. Evidence- rusty rocks because rust only forms when oxygen is present.
    • Evantually single and multicellular eukaryotes (plants) and then animals (cnidarians or other things in water) and then
    • Colonization of Land-


  9. The First Single-Celled Organisms
    • The oldest known fossils are stromatolites
    • 3.5 billion years ago
    • Prokaryotes were Earths sole inhabitants from 3.5 to about 2.1 billion years ago
  10. stromatolites
    • The oldest known fossils are stromatolites
    • 3.5 billion years ago
    • Prokaryotes were Earths sole inhabitants from 3.5 to about 2.1 billion years ago
  11. cyanobacteria
    • The early rise in O2 was likely caused by ancient cyanobacteria
    • A later increase in the rise of O2 might have been caused by the evolution of eukaryotic cells containing chloroplasts

  12. endosymbiont theory- one celll engulfed cyanobcteria and then it evolved as a symbiotic relationship
    Key evidence :
    • Inner membranes are similar to plasma membranes of prokaryotes
    • Division is similar in these organelles and some prokaryotes
    • These organelles transcribe and translate their own DNA
    • Their ribosomes are more similar to prokaryotic than eukaryotic ribosomes

  13. The Cambrian Explosion
    • sudden appearance of fossils resembling modern animal phyla (animals that look like us)
    • provides the first evidence of predator-prey interactions
    • Fossils in China provide evidence of modern animal phyla tens of millions of years before the Cambrian explosion
    • The Chinese fossils suggest that
    • the Cambrian explosion had a long fuse
    • (happened over a long period of time)


  14. The Colonization of Land
    • Fungi, plants, and animals began to colonize land about 500 million years ago
    • Arthropods (can invade air) and tetrapods are the most widespread and diverse land animals
    • Tetrapods evolved from lobe-finned fishes around 365 million years ago- has gills and lungs


  15. Plate Tectonics
    • At three points in time, the land masses of Earth have formed a supercontinent
    • Earths crust is composed of plates floating on Earths mantle

  16. Continental Drift (Pangea)
    • Formation of the supercontinent Pangaea about 250 million years ago had many effects
    • A deepening of ocean basins (when Eurasia combined there was less water for organisms to live in- colder and drier)
    • A reduction in shallow water habitat
    • A colder and drier climate inland
    • Continental drift has many effects on living organisms
    • A continents climate can change as it moves north or south
    • Separation of land masses can lead to allopatric speciation

  17. Formation of the supercontinent Pangaea about 250 million years ago had many effects
    • A deepening of ocean basins (when Eurasia combined there was less water for organisms to live in- colder and drier)
    • A reduction in shallow water habitat
    • A colder and drier climate inland

  18. Continental drift has many effects on living organisms
    • A continents climate can change as it moves north or south
    • Separation of land masses can lead to allopatric speciation

  19. Mass Extinctions
    • The fossil record shows that most species that have ever lived are now extinct
    • can be caused by changes to environment
    • result of disruptive global environmental changes
    • >50% of species became extinct

  20. A number of factors might have contributed to these extinctions
    • Intense volcanism
    • Global warming: CO2 from the volcanoes
    • Reduced temperature gradient from equator to poles
    • Oceanic anoxia (less 02) from reduced mixing of ocean waters

  21. How Did Humans Evolve?
    • The oldest hominin fossils are from Africa
    • Hominins: include humans and extinct humanlike primates

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