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Explore the fascinating journey of life on Earth, from the emergence of prokaryotes like bacteria to the evolution of mammals. Discover the key milestones in the evolutionary timeline, from the Cambrian explosion to the rise of amphibians, reptiles, birds, and mammals. Uncover the interconnectedness of different life forms and how they have adapted and evolved over billions of years.
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Melissa Harker Evolution of Life on Earth
Prokaryotes-first life form • We are closer to archaea than prokaryota (16s rRNA) • 3.8 billion years ago bacteria emerged, then oxygen-producing bacteria • Stromatolites and cyanobacteria evolved later • After 2.5 bya, increase in oxygen changed life forms...algae, etc.
Primitive eukaryotes • After protista, primitive worm-like creatures appeared • Sponges, cnidaria appreared, trilobites-first arthropod
Edicaran Fauna • Similar to jellyfish, no hard parts to make good fossils • 635-642 Ma
Cambrian explosion (540 Ma) • A result of the rise of oxygen? • Chordates (will explain later) • Most organisms from this period, trilobites, etc. died off • First vascular plants from algae, then ferns, then seed plants, gymnosperms, finally angiosperms • Ferns do not evolve into seed plants—they are an evolutionary dead end!
Primary Chordates • Jawless fish-most primitive • Hagfish have no backbone, lampreys do • Lungfish actually were not well-adapted, “advanced” fish • The Coelacanth is not the ancestor of amphibians
Amphibians • Evolved from a relative of the coelacanth • Key structure to life on land is the amniotic egg that reptiles, birds, and mammals have
Reptiles • Turtles closest to crocodiles genetically • Birds evolved from dinosaurs
Did not evolve from birds, even though the first mammals laid eggs. They are a separate spin off Marsupials evolved before placentals Mammals