hw 4 questions

• what was lord kelvins estimated age of the earth in the nineteenth century?

  no more than 100 million years
• why do present day species represent less than 1 percent of all the species that have ever lived?

  many life forms have become extinct
• what is macroevolution?

  describes largescale changes in organisms, typically occurring over millions of years
• how can methods like carbon or uranium dating help determine the approximate age of a fossil that does not contain any radioisotopes?

  by dating the rocks found above and below the fossil
• what is the approximate age of the oldest known rocks on earth, and what do they hint at?

  3.8 billion years old, they contain carbon deposits that hint at life
• when did eukaryotes likely evolve, and what condition facilitated their evolution?

  when oxygen reached 2-3 percent of present day levels, with their larger cells and greater energy needs
• what are some key innovations that land plants evolved to cope with the challenges of terrestrial life?

  Cuticle, vascular tissue, roots, seeds, specialized reproductive structures, leaves
• what are two effects of mass extinctions on the diversity of life?

  • entire groups of organisms perish, changing the history of life
  • the extinction of dominant groups of organisms that previously were of relatively minor importance, dramatically altering the course of evolution
• what are four mechanisms that can change the composition of a populations gene pool?

  Mutation, gene flow, genetic drift, natural selection.
• what is the ultimate source of all genetic variation, and what are some causes of gene mutations?

  Ultimate source: Mutations Causes of gene mutations:

  -spontaneous errors in DNA replication

  -exposure to mutagens like radiation or chemicals

  -collisions of DNA molecules with other molecules