L23 - Early Earth

  • Rules for Exam Preparation:

    • New review guides will provide all key ages to know.
    • Age abbreviations: Giga annum (Ga) = billions of years, Mega annum (Ma) = millions of years.
    • Relative order of evolutionary events is prioritized over exact ages unless specified in review guides.
    • Important evolutionary milestones include the emergence of land plants before amphibians.
    • Significant fossil names will be highlighted using bold, italics, and underlined text.
    • Innovations in evolution are crucial (e.g., Tiktaalik as a transitional species from fish to amphibians).

  • Geological Time Scale:

    • Overview of the geological time scale from the Precambrian through the Cenozoic.
    • Precambrian: 4.6 billion years ago (4500 Ma) to 541 million years ago (m.y.)
      • Hadean: 4.6 - 4.0 Ga. No preserved rocks.
      • Archean: 4.0 - 2.5 Ga, includes the oldest known rocks and fossils.
      • Proterozoic: 2.5 Ga to 541 Ma, includes rise of eukaryotes and transition to an oxygen-rich atmosphere.
    • Paleozoic: 541 - 252 Ma, includes Cambrian, Ordovician, Silurian, Devonian, Carboniferous, Permian periods.
    • Mesozoic: 252 - 66 Ma, includes Triassic, Jurassic, and Cretaceous periods.
    • Cenozoic: 66 Ma to present, includes Paleogene, Neogene, Quaternary periods.

  • Important Precambrian Events:

    • Origin of earth and the earliest conditions.
    • Earliest animal fossils appear around 541 Ma (Neoproterozoic).
    • Oldest known minerals, such as 4.4 billion-year-old zircons from Australia, indicate liquid water existed at that time.
    • Evidence of volcanic outgassing contributing to the formation of an early atmosphere (anoxic conditions).
    • Meteor impacts likely vaporized early oceans, contributing to climatic conditions.

  • Origin of Life Theories:

    • Abiogenesis: life originated from non-living matter under primordial conditions.
    • Panspermia: life (or its components) arrived via comets and meteorites.
    • Miller-Urey Experiment (1953): demonstrated organic molecules can be synthesized from primordial conditions, producing amino acids.
    • Conditions favorable for early life included presence of water, organic molecules, and energy sources like hydrothermal vents.

  • Evolution of Early Life:

    • Archaea: ancient life forms thriving in extreme conditions, different from eubacteria.
    • Archaea likely included thermophiles and methanogens, playing a role in early biosynthesis processes.

  • The Great Oxygenation Event:

    • Major increase in atmospheric oxygen due to photosynthesis in cyanobacteria.
    • Transition from an anoxic to an oxic atmosphere initiated around 2.5 Ga, leading to diverse life forms and banded iron formations (BIFs).
    • Banded Iron Formations indicate the build-up of atmospheric oxygen and occurred in sedimentary rocks.

  • Snowball Earth Hypothesis:

    • Major glaciations happened during the late Precambrian; hypotheses explore causes and effects on evolution.
    • Glaciation could have affected evolutionary rates and led to diversification in post-glacial periods.

  • Preservation of Fossils:

    • Different types of fossils include body fossils (unaltered or replaced), molds, casts, trace fossils (evidence of behavior or movement).
    • Soft parts are preserved under exceptional conditions (rapid burial and anoxic environments).
    • Early life relied on environments devoid of oxygen, potentially beneath sediments or in water bodies.