1.2 GTS

• Sedimentary Rocks- richest source of fossils. As a result, the fossil record is based mainly on the sequence in which fossils have accumulated in strata
• Fossils – preserved remains or traces of prehistoric life
• Index Fossils - basis for defining boundaries in the geologic time scale and for the correlation of the strata hence, also known as, guide fossils or indicator fossils
• Ammonites - most widely used index fossils as they are abundant, and can be easily identifies at species level
• Examples of index fossils:

  trilobite

  echinoid

  graptolite

  coral

  brachiopods

  ammonites
• Permineralization occurs when dissolved minerals carried by groundwater fill the cellular spaces of plants and animals. The dissolved minerals crystalize producing rocks in animal or plant shape. This is the most common type of fossil preservation
• Natural casts form when flowing water e all of the original bone or tissue, leaving an impression in sediment. Minerals fill in the mold, recreating the original shape of the organism (e.g. shells of marine invertebrates)
• 3. Amber preserved are organisms that become trapped in tree resin that hardens into amber after the tree gets buried underground (e.g. insects, pollen, lizards, and frog
• 4. Trace fossils record the activity of an organism (e.g. nests, burrows, imprints of leaves, footprints, and manure [referred to as coprolite]) (
• Preserved remains record intact remains of animals, often including preserved skin, muscle, bone, hair and internal organs. Fossils form when an entire organism becomes encased in material such as ice or volcanic ash or buried in peat bogs. This is a much rarer form of preservation than the other forms mentioned
• 5 ways a fossil can form:

  • Permineralization
  • Natural Cast
  • Amber preserved
  • Trace fossils
  • Preserved remains
• Stages of Fossilization

  1. organism dies and is buried before the remains are completely destroyed
  2. layers of sediment build up and press down on the buried remains over time
  3. transported di s solved material by groundwaters in the sediment fill tiny spaces in the bones which eventually turns sediments into rock and bones into mineralized fossils brought by the combination of pressure, chemical reactions, and time
  4. fossils remain within the rock until uncovered through erosion or excavation
• Limitiations of fossil record

  • incomplete chronicle of evolution
  • many are destroyed, only a fraction have been discovered
  • biased in favor of species that existed for a long time
• Carbon Dating

  • The order of fossils in rock strata tells us the sequence but not their actual ages.
• Relative Dating

  • determine the relative order of events but not their actual age
• Absolute/ Radiometric dating

  • uses half life to determine the age of a sample
• Half life

  • time required for 50% of the parent isotope to decay
• Ediacaran Fauna/ Biota

  • first multicelled metazoans that require atmospheric oxygen for their growth
• 2. Ichthyostega

  • interconnecting link between fishes and amphibians
• Seymouria

  • interconnecting link between amphibians and reptiles
• Hyracotherium

  • early ancestors of horses
• Dinosaurs

  • extinct group of reptiles
• Archaeopteryx

  ancestral form of birds
• Rodhocetus

  • ancient whale, has ankle bones that points to close evolutionary artiodactyls
• dorudon atrox

  • ancient toothed whale that lived abt 37 MYA
• Evolutionary Significance of fossils

  • origin and evolution
  • climatic conditions
  • phylogenetic discussions
  • genetic makeup
• eon?


  first and largest division of geologic time
• era?


  2 or more geological peiods
• period?


  basic unit of geological time, named either location or characteristics of the defining rock formations
• epoch?


  smallest division of GTS which represents the subdivision of a period
• Age?


  unit of GTS which is distinguished by some feature, shorter than epoch
• Hadean?


  first appearance of organic components of the building blocks of life (amino, acids, RNA and DNA)
• Arhcaean

  • oxygen-liberating photosynthesis originated, butt remained scarce
  • stromatolites, extremophiles and colonial cyanobacteria
• Proterozoic?

  • great oxygenation event
  • protists, green algae, edicarian biota
• The Great Oxygenation

  • occurred when cyanobacteria living in the oceans started producing oxygen via photosynthesis which completely transformed the atmosphere, causing the decimation of the anaerobic (non- oxygen) bacteria that existed at the time (Earth’s first mass extinction)
  • led to the formation of large deposits of iron
• Rodinia

  • neoproterozoic supercontinent that assembled 1.1–0.9 BYA and broke up 750–633 MYA
• Phanerozoic

  • divided into 3 eras: PMC
  • paleozoic
  • mesozoic
  • cenozoic
• cambrian

  • thallophytes were well establishes
  • coelenterates, arthorpods, echinoderms and mollusks
• trilobite

  • an extinct arthropod divided in 3 lobes
• Ordovician

  • marine algae, bryophytes, fungi, coral rocks, ostracoderm, jawless agnathan