How did life begin on Earth Origin of first cells Unique conditions on earth hot mostly ocean with volcanic gases and low oxygen levels 3 5 billion years ago Energy sources o geothermal heat UV light had a higher intensity than during present day lightning These all tend to breakdown complex molecules o Deep sea hydrothermal vents pH gradients within alkaline vent rocks Relatively more stable and friendly towards complex molecules Required abiotic steps o Formation of amino acids nitrogenous bases etc o Formation of proteins and nucleic acids o Packaging of cellular fundamentals within protocells with simple lipid membrane o Origin of self replicating RNA followed by DNA Earliest Evidence of Life The oldest cell fossils are prokaryotes in stromatolite formations o Stromatolites layered mats of bacteria and minerals How did new life begin Each lineage began with one species o New species arise from speciation due to microevolution followed by even more speciation Adaptive Radiation many diverse species coming from one ancestor o Promoted when new habitats become available o Often the arrival of new adaptations improve o Change in environments promote radiation or success extinction o Major radiations follow mass extinctions How did major changes in form arise Novelties may evolve gradually e x squid eye o Selection for a better eye pushed each generation to add on to the existing structure to make it better Exaptation existing adaptation gets gradually modified for another use e x feathers porcupine quils mammalian ear bone Evolution and development o Developmental genes control development of o Regulatory genes control when where and which multicellular organisms genes are expressed o Mutation of genes that regulate timing of expression leads to heterochrony o Paedomophisis change of timing in gene expression that produces a sexually mature adult with juvenile features o Mutations of homeotic genes affect placement of body parts o HOX genes are a type of homeotic gene
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