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Tamil Nadu Board of Secondary EducationHSC Science Class 12

Geological Time Scale

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CISCE: Class 12

Key Points: Geological Time Scale

  • The geological time-scale represents the entire history of the Earth and helps correlate geological and biological events in proper sequence.
  • The Earth’s crust is made of layered rocks, and radioactive dating techniques estimate the age of the Earth to be about 4.5 billion years.
  • Earth’s history is divided into five major eras: Archaeozoic, Proterozoic, Palaeozoic, Mesozoic, and Cenozoic.
  • Each era is further divided into periods and epochs, marked by changes in climate, plant life, and animal life.
  • The time-scale shows the gradual evolution of life, from simple unicellular organisms to complex plants, animals, and humans.
  • Major events such as the origin of life, rise and extinction of dinosaurs, and evolution of mammals and humans are recorded in the geological time-scale.
  • Scientists believe Earth is currently entering a sixth mass extinction (Anthropocene), mainly due to human activities causing rapid loss of biodiversity.
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