March Monthly Exam

• The Earth is approximately 4.6 billion years old
• Comparing the Earth's age to one calendar year, events such as the extinction of dinosaurs and the re-discovery of the New World by Columbus would appear relatively much easier
• Understanding the geologic time scale reminds us of our time and place in the universe
• Geologic Time


  It is very, very long
• The Earth is estimated to be around 4.6 billion years old based on the rock and fossil record
• Geologic time


  Broken up into sections based on major changes in Earth
• Largest Division of Geologic Time

  • Eons
• Eons are divided into

  • Eras: PreCambrian, Paleozoic, Mesozoic, Cenozoic
• Ceno


  Recent
• Meso


  Middle
• Paleo


  Ancient
• Zoic


  Life
• Eras are divided into

  • Periods
• PreCambrian Era


  • 543 million years ago to ~ 4 billion years ago
  • Age of Bacteria
  • Oldest Era
  • Longest era because we know so little about the earth that long ago
  • Life: Very little life, only basic forms including bacteria, the oldest fossils ever found, seaweed, jellyfish, and worms
  • Photosynthesis of the seaweed added oxygen to the early atmosphere, paving the way for land life
• Paleozoic Era


  • 543 million years ago to 248 million years ago
  • Age of the Fish
  • Explosion of life in the sea: trilobites, shellfish, Fish
  • Life appears on land: Ferns, Amphibians
  • Pangaea formed
  • Largest mass extinction ever at the end of the Paleozoic, 90% of species became extinct
• Mesozoic Era


  • 248 mya - 65mya
  • Age of the Reptiles
  • Life: Reptiles are the dominant life on land, Dinosaurs exist, Birds appear, Forests of trees appear
  • Pangea broke apart during this period
  • Dinosaurs become extinct in a mass extinction at the end of the Mesozoic
• Cenozoic Era


  • 65 mya - present
  • Age of the Mammals
  • Life: Large mammals appear, Humans appear
  • Ice Ages occur and ice sheets advance
• Cambrian Explosion


  The belief that there was a sudden, apparent explosion of diversity in life forms about 545 million years ago, creating the complexity of multi-celled organisms in a relatively short time frame of 5 to 10 million years, and creating most of the major extant animal groups today
• Eon


  The largest division of the geologic time scale, spanning hundreds to thousands of million of years ago (mya)
• Era


  A division in an Eon that spans time periods of tens to hundreds of millions of years
• Period


  A division of geologic history that spans no more than one hundred million years
• Epoch


  The smallest division of the geologic time scale characterized by distinctive organisms
• The start of the Cambrian was characterized by the breaking up of supercontinent Gondwana into smaller land masses opening up new environmental niches where organisms can colonize and specialize
• Fossils


  The remains or traces of organisms from a past geologic age embedded in rocks by natural processes
• Fossils are extremely important for understanding the evolutionary history of life on Earth, as they provide direct evidence of evolution and detailed information on the ancestry of organisms
• Analogous Structure - structures that may have the same function but different structure; do not come from common descent
• Homologous structure - organ or bone that is derived from a common ancestor
• Vestigial structure - reduced body parts that have little to no function; remnant of an ancestor
• Embryology is the patterns of embryological development that can indicate a common ancestry
• Biochemical structure - the more closely related organisms are, the more similar the biochemical makeup
• Universality of genetic code supports evolution
• Chlorophyll is the basic molecules in all photosynthetic organisms
• Categories of Fossils

  Any indirect evidence left by an organism is a trace fossil.
• Categories of Fossils

  Molds and casts - mold is an impression of an organism; cast is a mold filled with sediment
• Categories of Fossil

  Replacement - original material is replaced with mineral crystals that can leave detailed replicas of hard or soft parts
• Categories of Fossils

  Amber is a preserved sap traps an entire organism. The sap hardens and preserved the trapped organism.
• Categories of Fossils

  Original material - mummification or freezing preserves original organisms
• Unaltered preservation - Small organism or part trapped in amber, hardened plant sap.
• Per mineralization or Petrification - The organic contents of bone and wood are replaced with silica, calcite or pyrite, forming a rock-like fossil.
• Replacement - hard parts are dissolved and replaced by other minerals, like calcite, silica, pyrite, or iron.