Extinction + Genesis

• Ordovician extinction


  440 mya, small marine organisms died out
• Devonian extinction


  365 mya, many tropical marine species went extinct
• Permian extinction


  250 mya, largest mass extinction event ever, wiped out a giant range of species, including several vertebrates
• Triassic extinction


  210 mya, the extinction of many other vertebrate land species that allowed for dinosaurs to flourish
• K-T extinction


  65.5 mya, when an asteroid hit earth and wiped out all non-avian dinosaurs, and 50% of earth's plants and animals
• Changes in environment


  Primary reason that species go extinct
• Stromatolytes


  Structures made up of layers of cyanobacteria that fossilized, giving us the earliest fossils from 3.5 bya
• Oparin-Haldane hypothesis


  That life on earth could have arisen step-by step from non-living matters through a process of gradual chemical evolution
• Oparin and Haldane's hypothesis worked with:

  • Simple organic molecules could have reacted to form building blocks like amino acids, which turned oceans into a primordial soup
  • Blocks could have combined to form polymers and nucleic acids
  • Polymers could have developed into ways where they were capable or replicating themselves
• Miller and Urey experiment


  Built a model based on old assumptions about the conditions of early earth from the 1920s and then waited for a week. Found that amino acids started to form but no DNA yet
• Genes first hypothesis


  Idea that the earliest life was just self-replicating DNA or RNA and that more complicated metabolic systems got added on later
• RNA world hypothesis


  Version of the genes first hypothesis that most scientists subscribe to, where they think that RNA was the first genetic material to exist because it can also act as a catalyst, which would have been important in a time before any other real catalysts, in order to actually reproduce
• Metabolism first hypothesis


  Idea that the earliest life forms were just self-sustaining metabolic reactions, and nucleic acids came later, after molecules sustained from the metabolic events acted as catalysts that allowed for more complex biomolecules
• The RNA world hypothesis has speculation about one RNA grabbing on to another RNA, which would act like an rRNA, which existed long before RNA proteins, to start building more RNA