Geological Time Scale, Fossils, Mass Extinction

• Geological Time Scale is a record of life forms and geological events in Earth's history
• Scientist developed the time scale by studying rock layers and fossils worldwide
• Geological Time Scale


  Has 4 categories: Eons, Era, Periods, and Epochs
• Precambrian life


  • Hadean
  • Archean
  • Proterozoic eons
• Precambrian life started more than 550 million years ago
• Phanerozoic Eon


  • Paleozoic
  • Mesozoic
  • Cenozoic
• Paleozoic Era


  • Cambrian
  • Ordovician
  • Silurian
  • Devonian
  • Mississippian
  • Pennsylvanian
  • Permian
• During the Paleozoic Era, marine invertebrates, fishes, and the age of amphibians were formed
• Mesozoic Era


  • Triassic
  • Jurassic
  • Cretaceous
• The most significant land mass activity in the Mesozoic Era was the gradual rifting of the supercontinent Pangaea
• The predominant animals in the Mesozoic Era were reptiles due to their ability to withstand drier climates
• Small mammals and birds also thrived in the Mesozoic Era because they were warm-blooded and had hair or feathers to protect them from changing climate
• Cenozoic Era


  • Paleogene
  • Neogene
  • Quaternary
• The world's great mountain ranges were built during the Cenozoic Era, contributing to the cooling down of the climate
• The Cenozoic Era is known as the Age of Mammals, when mammals began to increase and evolve adaptations to live in many different environments
• Grasses also increased in the Cenozoic Era and provided a food source for grazing animals, allowing them to increase in population
• Modern humans emerged during the Pleistocene epoch of the Cenozoic Era
• Molds


  Impression made in a substrate = negative image of an organism
• Casts


  When a mold is filled in
• Petrified


  Organic material is converted into stone
• Original Remains


  Preserved wholly (frozen in ice, trapped in tar pits, dried/desiccated inside caves in arid regions or encased in amber/fossilized resin)
• Carbon Film


  Carbon impression in sedimentary rocks
• Trace/Ichnofossils


  Record the movements and behaviors of the organism
• Six Ways of Fossilization

  • Unaltered Preservation
  • Permineralization/Petrification
  • Replacement
  • Carbonization or Coalification
  • Recrystallization
  • Authigenic preservation
• Relative Dating


  Does not tell the exact age, only compares fossils as older or younger based on their position in rock layer
• Rules of Relative Dating

  • Law of Superposition
  • Law of Original Horizontality
  • Law of Cross-Cutting Relationship
• Absolute Dating


  Determine the actual age of the fossil through radiometric dating, using radioactive isotopes carbon-14 and potassium-20
• Change in the environment often create new niches (living spaces) that contribute to rapid speciation and increased diversity
• Cataclysmic events, such as volcanic eruptions and meteor strikes that obliterate life, can result in devastating losses of diversity
• Mass extinctions have occurred repeatedly in the evolutionary record of life, erasing some genetic lines while creating room for others to evolve into the empty niches left behind
• The end of Permian period (and the Paleozoic Era) was marked by the largest mass extinction event in Earth's history, a loss of roughly 95% of the extant species at that time
• Some of the dominant phyla in the world's oceans, such as trilobites, disappeared completely during the Permian mass extinction
• On land, dominant species of Permian reptiles disappeared, then new line of reptiles emerged, the dinosaurs
• The warm and stable climatic conditions of the ensuing Mesozoic era promoted an explosive diversification of dinosaurs into a very conceivable niche in land, air, and water
• Another mass extinction occurred at the end of the Cretaceous period, bringing the Mesozoic era to an end
• Skies darkened and temperature fell as a large meteor impact and tons of volcanic ash blocked incoming sunlight, causing plants to die, herbivores and carnivores to starve, and the mostly cold-blooded dinosaurs to cede their dominance of the landscape to the warm-blooded mammals
• In the following Cenozoic Era, mammals radiated into terrestrial and aquatic niches once occupied by dinosaurs, and birds, the warm-blooded offshoots of one line of the ruling reptiles, became aerial specialists