Bio

• Earth has a very long history
• Geological time scale


  A record of how Earth and its life forms have changed through time
• The geological time scale is divided into eons, eras, periods, and epochs
• Geological time scale


  • Divisions have no fixed lengths, instead they are based on changes or events recorded in rocks and fossils
• Eons in the geological time scale

  • Precambrian time
  • Paleozoic Era
  • Mesozoic Era
  • Cenozoic Era
• Periods in the Paleozoic Era

  • Cambrian
  • Ordovician
  • Silurian
  • Devonian
  • Carboniferous
  • Permian
• Periods in the Mesozoic Era


  • Triassic
  • Jurassic
  • Cretaceous
• Periods in the Cenozoic Era

  • Tertiary
  • Quaternary
• The Proterozoic


  1. No life possible as the Earth initially forms 4.6 billion years ago

  2. Simple, single-celled forms of life appear 3.8 billion years ago, becoming more complex and successful over the next 3 billion years: Prokaryotes then Eukaryotes

  3. Cyanobacteria begins producing free oxygen (photosynthesis)

  4. Land masses gather to make up a continent called "Rodinia"
• The Cambrian


  1. Explosion of life

  2. All existing phyla come into being at this time

  3. Life forms in warm seas as oxygen levels rise enough to support life

  4. Dominant animals: Marine invertebrates (trilobites and brachiopods)

  5. Supercontinent Gondwana forms near the South Pole (note position of present-day Florida)
• The Ordovician


  1. The 1st animals with bones appear, though dominant animals are still trilobites, brachiopods and corals

  2. The beginning of the construction of South Carolina

  3. A very cold time in Earth's history: there was a great extinction due to ice caps in present-day Africa

  4. Four main continents: Gondwana, Baltica, Siberia and Laurentia
• The Silurian


  1. First land plants appear and land animals follow

  2. Laurentia collides with Baltica and closes lapetus Sea

  3. Coral reefs expand and land plants begin to colonize barren land

  4. First millipede fossils and sea scorpions (Euryptides) found in this period
• The Devonian (Age of the Fish)

  1. Pre-Pangea forms. Dominant animal: fish

  2. Oceans still freshwater and fish migrate from southern hemisphere to North America

  3. Present-day Arctic Canada was at the equator and hardwoods began to grow

  4. Amphibians, evergreens and ferns appear

  5. The Acadian Orogeny, leading to S.C. metamorphism
• The Mississippian


  1. First seed plants appear

  2. Much of North America is covered by shallow seas and sea life flourishes (bryoza, brachipods, blastoids)
• The Pennsylvanian


  1. Modern North America begins to form

  2. Ice covers the southern hemisphere and coal swamps formed along equator

  3. Lizards and winged insects first appear
• The Permian


  1. Pangea forms. Reptiles spread across continents

  2. The Appalachians rise

  3. 90% of Earth's species become extinct due to volcanism in Siberia. This marks the end of trilobites, ammonoids, blastoids, and most fish
• The Triassic


  1. First dinosaurs appear

  2. First mammals- small rodents appear

  3. Life and fauna re-diversify

  4. Rocky Mountains form

  5. First turtle fossil from this period

  6. Pangea breaks apart
• The Jurassic


  1. Pangea still breaking apart

  2. Dinosaurs flourish "Golden age of dinosaurs"

  3. First birds appear

  4. North America continues to rotate away from Africa
• The Cretaceous


  1. T-Rex develops

  2. First snakes and primates appear

  3. Deciduous trees and grasses common

  4. First flowering plants

  5. Mass extinction marks the end of the Mesozoic Era, with the demise of dinosaurs and 25% of all marine life
• 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
• Ways to measure the age of a fossil

  • Relative dating
  • Absolute dating
• Relative dating

  Based upon the study of layers of rocks, does not tell the exact age, only compares fossils as older or younger depending on their position in the rock layers
• Rules of relative dating

  • Law of Superposition
  • Law of Original Horizontality
  • Law of Cross-Cutting Relationships
  • Index Fossils
• Absolute dating


  Determines the actual age of the fossil through radiometric dating, using radioactive isotopes like carbon-14 and potassium-40
• Six ways of fossilization

  • Unaltered preservation
  • Permineralization/Petrification
  • Replacement
  • Carbonization or Coalification
  • Recrystallization
  • Authigenic preservation
• Mutation


  A change in the DNA sequence of an organism, can result from errors in DNA replication, exposure to mutagens, or viral infection

  
• Although mutation is the original source of all genetic variation, mutation rate for most organisms is pretty low, so the impact of brand-new mutations on allele frequencies from one generation to the next is usually not large

  
• Natural selection


  A mechanism of evolution where organisms that are more adapted to their environment are more likely to survive and pass on the genes that aided their success, causing species to change and diverge over time
• Gene flow


  The movement of genes into or out of a population, due to either the movement of individual organisms or their gametes
• Genetic drift


  The change in frequency of an existing gene variant in the population due to random chance, which can cause gene variants to disappear completely or become much more frequent

  
• Gene flow


  The movement of genes into or out of a population, due to either the movement of individual organisms or their gametes (e.g. through pollen dispersal by a plant)

  
• Gene flow


  • Can be a strong agent of evolution
• Genetic drift


  The change in frequency of an existing gene variant in the population due to random chance

  
• Genetic drift


  • May cause gene variants to disappear completely and thereby reduce genetic variation
  • May cause initially rare alleles to become much more frequent, and even fixed

  
• Genetic drift


  • Involves changes in allele frequency due to chance events - literally, "sampling error" in selecting alleles for the next generation
  • Has a stronger effect on small populations

  
• Hardy-Weinberg law


  The law that states that in an infinitely large, interbreeding population in which mating is random and in which there is no selection, migration, or mutation, gene and genotype frequencies will remain constant from generation to generation
• In practice, the conditions for the Hardy-Weinberg law are rarely strictly present, but unless any departure is a marked one, there is no statistically significant movement away from equilibrium
• Hardy-Weinberg equation


  p^2 + 2pq + q^2 = 1, where p is the frequency of the "A" allele and q is the frequency of the "a" allele in the population
• Conditions for genetic equilibrium under the Hardy-Weinberg law

  • No mutation (change) in the DNA sequence
  • No migration (moving into or out of a population)
  • A very large population size
  • Random mating
  • No natural selection
• Problem 1: Calculating genotype and allele frequencies

  Given: 36% homozygous recessive (aa) genotype

  a. Frequency of aa genotype = 36%

  b. Frequency of a allele = 60%

  c. Frequency of A allele = 40%

  d. Frequency of AA genotype = 16%, Frequency of Aa genotype = 48%

  e. Frequency of dominant phenotype = 64%, Frequency of recessive phenotype = 36%