History of Life on Earth

Lecture 9: History of Life on Earth

Formation of Earth

  • Age of Earth: 4.56 billion years ago (bya)

    • Jack Hills Zircon: oldest known material on Earth.

    • Core and Moon Formation: Early stages in Earth's development.

    • Late Heavy Bombardment: Period of intense meteorite impacts.

  • Geological Eras:

    • Hadean: Formation of the Earth, molten surface, and development of atmosphere.

    • Archean: Formation of first stable continental crust and oceans.

    • Proterozoic: Rise of oxygen and emergence of eukaryotic life.

    • Phanerozoic: Development of complex life forms and multicellularity.

Key Events

  • 3.5 bya: First cells with nuclei appear.

  • 2.5 bya: Great Oxygenation Event due to photosynthetic bacteria.

  • 600 mya: Simple animals emerge.

  • 550 mya: Complex animals evolve.

  • 430 mya: Land plants begin to develop.

  • 360 mya: Tetrapod animals come onto land.

Expansion of the Universe

Current Understanding

  • Age of the Universe: 13.8 billion years ago (bya).

    • Expansion is observed through redshift as galaxies move away from us.

  • Current Rate of Expansion: 73.5 ± 1.4 km/sec/Mpc (Mega parsecs).

Galaxy Formation

  • 1 billion years: Evidence of galaxy clusters forming due to gravitational coalescence of matter in the early universe.

Formation of Stars and Planets

Star Birth Cycle

  1. Nebulae Formation: Massive clouds of gas and dust in interstellar space.

  2. Clump Formation: Dense areas within the nebula begin to coalesce to form stars.

  3. Core Development: Dense cores form, leading to star birth.

  4. Accretion of Planets: Disks around young stars accumulate materials into planets through accretion.

Specific Examples of Star Systems

  • Stars forming include DMTau, V1247Ori, and others as noted by NASA/ESA imagery.

Geological Periods

Hadean Era

  • Earth cools: Initial cooling phase after formation, leading to stabilization of the crust.

  • Development of an anoxic atmosphere and formation of liquid water by 4.1 bya.

Archean Era (4,600 - 2,500 mya)

  • Emergence of prokaryotic life, first evidence of life in sedimentary rocks.

Proterozoic Era (2,500 - 543 mya)

  • Rise of oxygen levels due to phototrophic organisms and diversification of life forms.

    • First eukaryotic cells and multicellular life.

Phanerozoic Era (543 mya - Present)

  • Paleozoic Era: Emergence and evolution of marine invertebrates, first fish, land plants, and amphibians.

    • Mesozoic Era: Age of dinosaurs, flowering plants, and substantial tectonic activity.

    • Cenozoic Era: Evolution of mammals and birds post-dinosaur extinction, leading to modern ecosystems.

Major Fossil Evidence

  • Modern stromatolites dated back to 3.5 bya, highlighting the history of early life on Earth.

  • Banded Iron Formations: Evidence of oxygen-producing photosynthetic organisms around 2.5 bya.

  • Emergence of complex multicellular organisms and their fossils noted around 600 mya and onwards for land plants and vertebrates.