History of Life on Earth Notes

How Old is Earth?

  • Estimated age: 4.5 billion years old.
  • Alexander Ivanovich Oparin: Proposed early Earth's reactive atmosphere and "primordial soup" oceans.

Origin of Life

  • Stanley Miller and Harold Urey: Experiment simulating early atmosphere with hydrogen, methane, ammonia, and water, yielding amino acids.
  • Microscopic cell-like structures appeared 200-300 million years ago.
    • Protenoid microspheres: Selectively permeable membrane; simple energy storage/release.
  • Possible locations:
    • Soil surfaces
    • Interstellar space
    • Atmosphere
    • Oceans (though less likely due to high sodium and chlorine content)

Origin of Eukaryotic Cells

  • Endosymbiosis: Organism lives inside another.
  • Endosymbiotic theory: Eukaryotic cells formed symbiotic relationships with prokaryotic organisms.

Paleontology

  • Study of the history of life, including the origin and extinction of different groups.
  • Focuses on fossil remains, ecologies of the past, and organism evolution.
  • Example: Archaeopteryx lithographica shows dinosaur ancestry of birds

Geology

  • The study of rocks and Earth's materials

Geologic Time Scale

  • Calendar of Earth's history arranged chronologically.
  • Developed by studying rock layers and index fossils.
  • Divisions: Eon, Era, Period, Epoch.

Divisions of Geologic Time Scale

  • Eons: Largest divisions (hundreds of millions of years).
    • Phanerozoic: Organisms with skeletons or hard shells.
    • Proterozoic: First multicellular organisms; mass extinction.
    • Archaeozoic: First single-celled organisms.
    • Hadean: Earth's formation from dust and gases.
  • Precambrian Time: Proterozoic, Archaeozoic, and Hadean eons (almost 90% of Earth’s history).
  • Eras: Smaller time intervals within eons.
    • Phanerozoic divided into Paleozoic, Mesozoic, and Cenozoic.

Eras

  • Paleozoic: Marine organisms
  • Mesozoic: Age of Reptiles/Dinosaurs, appearance of flowering plants.
  • Cenozoic: Age of Mammals

Periods

  • Subdivisions of eras.
    • Proterozoic: Vendian/Ediacaran (soft-bodied underwater life).
    • Paleozoic: Cambrian, Ordovician, Silurian, Devonian, Carboniferous, Permian.

Periods Explained

  • Cambrian: Hard body parts evolved; most animal phyla appeared.
  • Ordovician and Silurian: Early cephalopods.
  • Devonian: Plants adapted to land; Age of Fishes.
  • Carboniferous and Permian: Reptiles evolved from amphibians.
  • Mesozoic: Cretaceous, Jurassic, and Triassic periods (age of dinosaurs).

Mesozoic Periods

  • Triassic: Dinosaurs appeared (e.g., Coelophysis).
  • Jurassic: Dinosaurs dominated land; Archeopteryx appeared.
  • Cretaceous: Reptiles were dominant; new dinosaurs evolved; meteorite-caused mass extinction.

Cenozoic Era

  • Divided into Tertiary and Quaternary periods.
    • Tertiary: Warm climate; flowering plants and grasses flourished.
    • Quaternary: "Age of Man"; ice ages; Homo sapiens evolved.

Epochs

  • Finer subdivisions (Cenozoic and parts of Mesozoic eras).
  • Geologic timescale is used to identify past organisms.