fossil record

• Fossil records, comparative anatomy, and genetic information provide evidence for evolution
• Original tissues can be preserved as fossils
• Organisms become extinct only in mass extinction events
• Environmental change causes variations in populations
• Variations can lead to adaptations
• Living species contain no evidence that they are related to each other
• Plants and animals share similar genes
• How fossils form


  1. Soft tissues break down, only hard parts remain

  2. Hard parts become fossilised under rare conditions
• How scientists date fossils

  1. Relative-age dating

  2. Absolute-age dating using radioactive decay
• Fossils are evidence of biological evolution
• Fossil record


  All the fossils ever discovered on Earth
• The fossil record provides evidence that species have changed over time
• Scientists can recreate the physical appearance of species that are no longer alive on Earth based on fossil evidence
• Permineralization


  Most common fossilization process, minerals fill pores and preserve structure
• Carbonization


  Organic matter converted to carbon film
• Amber fossilization


  Organism preserved in hardened tree resin
• Freezing


  Organism preserved in ice
• Mummification


  Organism preserved through desiccation in dry environment
• Mold


  Impression of an organism in rock
• Cast


  Fossil copy of an organism in rock
• Carbon film fossils


  Delicate details of leaves and animal parts preserved
• Petrified fossils


  Organism's remains turned to stone by mineral-rich water
• Body fossils


  Actual remains of an organism
• Trace fossils


  Marks or impressions left by an organism
• Determining a fossil's age

  1. Relative-age dating

  2. Absolute-age dating using radioactive decay
• Fossils in older layers are more primitive than those in upper layers
• Extinct fossils resemble modern animals, showing common ancestry
• Geologic time scale


  Chart dividing Earth's history into different time units
• Extinction


  Last individual organism of a species dies
• Mass extinction


  Many species become extinct within a few million years or less
• Extinctions can occur when environments change
• The fossil record contains evidence of the appearance of many new species over time
• Biological evolution


  Change over time in populations of related organisms
• The fossil record is evidence that horses descended from organisms for which only fossils exist today
• Comparative anatomy


  Study of similarities and differences among structures of living species
• Homologous structures


  Body parts similar in structure and position but different in function
• Analogous structures


  Body parts that perform a similar function but differ in structure
• Vestigial structures


  Body parts that have lost their original function through evolution
• Embryology


  Science of the development of embryos from fertilization to birth
• Molecular biology


  Study of gene structure and function