fossil and changes

• 4.6 billion years ago Earth formed
• after about 500 million years solid crust formed on the surface
• Volcanoes erupted and meteorites hit the surface
• Earth eventually cooled, and liquid water formed on the surface, forming the first oceans
• 500 million years ago, life appeared
• Natural selection, mutations, genetic drift, and gene flow are the mechanisms that cause changes in allele frequencies over time.
• Natural selection is the main way in which populations evolve. 
• Charles Darwin and Alfred Russell Wallace noticed that there is always a struggle for survival among members of a population due to the fact that resources are always limited. This means only a portion of the offspring born in every generation will survive. 
• A mutation is a source of new alleles in a population, thus it leads to an increase in variation among the members of the population. 
• A mutation is a change in the DNA sequence of the gene. 
• A negative mutation affects the phenotype of the organism in a way that gives it reduced fitness—a lower likelihood of survival, resulting in fewer offspring.
• A positive mutation produces a phenotype with a beneficial effect on fitness.
• Many mutations, called neutral mutations, will have no effect on fitness.
• Gene flow can occur when an individual travels from one geographic location to another and joins a different population of the species.
• Genetic drift always leads to a reduction in the variation present in a population. 
• Genetic drift is most important in small populations. Drift would be completely absent in a population with infinite individuals, but, of course, no population is this large.
• Genetic drift in a population can lead to the elimination of an allele from a population by chance. 
• The frequency of alleles in the next generation is equal to the frequency of alleles among the individuals reproducing.
• Hardy-Weinberg Equilibrium- the principle that states that in an infinitely large, interbreeding population in which mating is random, and there is no selection, migration, or mutation, gene and genotype frequencies will remain constant from generation to generation.
• THE FIVE CONDITIONS THAT MUST BE MET FOR GENETIC EQUILIBRIUM TO OCCUR: 

   

  1. No mutation in the DNA sequence

  2. No migration 

  3. A very large population size

  4. Random mating 

  5. No natural selection
• A fossil is any preserved evidence of an organism
• For an organism to be preserved as a fossil, it must be buried quickly in sediment
• sedimentary rock, such as limestone, shale, or sandstone
• mold and cast
• types of fossils

  • perified
  • original remains
  • carbon film
  • trace/ichnofossils
• Unaltered preservation - Small organism or part trapped in amber, hardened plant sap.
• Permineralization/ 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.
• Carbonization or Coalification – The other elements are removed, and only the carbon remained.
• Recrystallization - hard parts are converted to more stable minerals, or small crystals turn into larger crystals
• Authigenic preservation - molds and casts are formed after most of the organism have been destroyed or dissolved
• Relative Dating

  1. law of superposition
  2. law of original horizontality
  3. Law of cross-cutting relationships
  4. index fossils
• Law of superposition Younger layers of rock

  sit atop older layers.
• Law of original horizontality

  Layers of sedimentary rock are originally deposited flat.
• Law of cross-cutting relationships Rock layers A and B must be older than the intrusion (C) that disturbs them.
• Law of lateral continuity Layers of rock are continuous until they encounter other solid bodies that block their deposition or until they are acted upon by agents that

  appeared after deposition took place.
• can determine

  Age of fossil with respect to another rock or fossil (that is, older or younger

  relative dating
• can determine age of a fossil in hears

  absolute dating
• is performed by Comparing depth of a fossil's source stratum to the position of a reference fossil or roc

  relative dating
• Is performed by Determining the relative amounts of a radioactive isotope and nonradioactive isotope in a specime

  absolute dating