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Brief Account of Evolution

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Estimated time: 3 minutes
CBSE: Class 12

Key Points: Brief Account of Evolution

  • First Life Forms - 2000 mya; first cells appeared, some released O₂; single-celled → multicellular.
  • Aquatic to Land - 500 mya invertebrates; 350 mya jawless fish; strong-finned fish moved onto land.
  • Amphibians → Reptiles - Reptiles laid thick-shelled eggs; dominated Earth for 200 million years; giant ferns formed coal.
  • Mesozoic Era - 200 mya some reptiles returned to water (e.g., Ichthyosaurs); T. rex dominated land (20 feet tall).
  • Dinosaur Extinction - 65 mya, dinosaurs suddenly disappeared due to climatic changes or evolved into birds.
  • Rise of Mammals - Shrew-like, viviparous, intelligent; replaced reptiles as dominant life forms.
  • Continental Drift - South American mammals were overridden by North American fauna; Australian marsupials survived due to no competition.
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