Fossils

• Fossils


  Remains or traces of living things that existed thousands or millions of years ago

  
• Types of fossils


  • Impressions of plant leaves in a rock
  • Tracks left behind by animals
  • Ancient dens
  • Barrels
  • Whole animal or insect perfectly preserved and crystallized by ice

  
• The oldest fossils come from mats of blue-green algae that existed over 3 billion years ago

  
• The youngest fossils come from animals that existed before the start of recorded history, about 10,000 years ago
• How fossils are formed

  1. Living matter such as plants, animals, and other organisms die and are buried beneath layers of rock and dust known as sediment

  2. Pressure and heat cause the tissue of the dead organism to emit oxygen and hydrogen, leaving a residue of carbon behind (carbonization or distillation)

  3. Carbonization gives birth to a carbon impression of the dead organism in the sedimentary rock (fossilization)

  4. Permineralization (petrification) is the most common technique of fossilization, where the hardest parts of the organism absorb water and minerals, forming crystals that harden the remains together with the outer sedimentary rock
• Six ways organisms can turn into fossils

  • Unaltered preservation (like insects or plant parts trapped in amber)
  • Permineralization=petrification (minerals seep in and replace organic tissues)
  • Replacement (hard parts dissolve and are replaced by other minerals)
  • Carbonization=coalification (only carbon remains)
  • Recrystalization (hard parts revert to more stable minerals or small crystals turn into larger crystals)
  • Authigenic preservation (molds and casts of organisms that have been destroyed or dissolved)
• Imprints


  Shallow external molds left by animal or plant tissues with little or no organic materials present
• Compression


  The other side of an imprint with more organic material
• Mold fossils


  Depressions on the rock, shaped like the part of the organism, left behind after the dead plant or animal decomposes
• Cast fossils


  Form when the mold is filled with another material after the total decay of the organism or part of the organism
• Trace fossils

  Tracks, burrows, borings and feces left behind by animals, providing indirect evidence of past life
• Petrified fossils


  Fossils where minerals replace the hard parts of organisms
• True-form fossils


  Fossils of entire bodies of plants or animals, usually formed when they are trapped in ice, tar or tree sap
• Types of fossils


  • Insect preserved in amber
  • Petrified wood (permineralization)
  • Cast and mold of a clam shell
  • Pyritized ammonite
  • Compression fossil of a fern

  
• Most fossils were commonly found in sedimentary rocks and were from the hard parts of the organism like woody stem, bones, or teeth
• A scientist who studies fossils is called a paleontologist
• The different types of fossils are: imprints, mold fossils, cast fossils, trace fossils, petrified fossils, and true-form fossils

  
• How fossils are formed


  Described in detail earlier

  
• Geologic Time SCALE

  
• Homologous structures


  Structures that may perform different functions in the species living in the different environment, or have the same origin but different functions
• Homologous structures


  • Forelimbs of dog, bird, lizard, and whale - structurally the same, but functionally different
• Analogous structures


  Structures of unrelated species that may evolve to look alike, because the structure is adapted to similar function
• Analogous structures


  • Wings of birds, bats, and insects - have the same function but different in origin
• Divergent evolution


  Produces homologous structures
• Convergent evolution


  Produces analogous structures
• Homologous structures


  Have similar anatomy but dissimilar functions
• Analogous structures


  Have dissimilar anatomy but similar functions
• Divergent evolution proposed that homologous structures that developed from common ancestors may have different functions, such as bat wings and rodent forelimbs
• Convergent evolution suggests that analogous structures of organisms of different ancestors have similar function such as butterfly wings and bird wings
• The presence of homologous structures is a strong indicator that the organisms evolved from common ancestors
• Divergent evolution


  The splitting of an ancestral population into two or more subpopulations that are geographically isolated from one another
• Convergence


  An increase in similarities among species derived from different ancestors as a result of similar adaptation to similar environment
• In convergent evolution, analogous structures of unrelated organisms from different ancestors develop similar function such as butterfly wings and bird wings
• Evolution


  Gradual change of organisms over time where modern organisms have descended from ancient organisms and keep on replacing it to fill the niches they left
• Evolution is considered as a gradual change of organisms over time
• Evolution theory


  A scientific framework that explains how life on earth has changed overtime through processes like natural selection, genetic variation, and adaptation to different environments
• Jean Baptiste de Lamarck


  Concluded that organisms of higher complexity had evolved from pre-existing, less complex organisms
• Lamarckism


  A theory of evolution based on the principle that physical changes in organisms during their lifetime such as greater development of an organ or a part through increase use could be transmitted to their offspring
• Theories developed by Lamarck

  • Theory of Need
  • Theory of Use and Disuse
  • Theory of Acquired characteristics
• Theory of Need


  Organisms change in response to their environment. Their ability to survive helped them develop characteristics necessary for them to adapt in a given environment