History of Life

Intro to Evolution and the History of Life

Key Concepts of Scientific Theory

  • Scientific Theory Definition: A scientific theory is a well-substantiated explanation of some aspect of the natural world that is based on a body of evidence, repeatedly tested through observation and experimentation.

    • Must withstand: Testing, multiple lines of evidence, and peer debate.

Importance of Evolution Theory in Biology

  • Life's History: Evolution shows how life has changed over time.

  • Common Ancestry: All species share common ancestors, similar to familial relations.

  • Explanation of Biological Structures: Explains behavior, structure, and functions of living organisms.

  • Distinction Between Evolution and Origins:

    • Evolution = Change and diversification following the appearance of life.

    • Origin theories explain how life arose from non-living matter.

Early Earth and Abiogenesis

  • Conditions Favoring Abiogenesis:

    1. Formation of biomolecular building blocks (e.g., amino acids).

    2. Self-assembly of these blocks into biomolecules.

    3. Formation of protocells (primitive cells).

    4. Cells that can replicate and pass on genetic information.

Theories of Life's Origins

  • Abiogenesis: Concept that life arose from non-life.

  • Hypotheses for the Origin of Life:

    • Miller-Urey Experiment: Suggested that early Earth conditions (with methane, ammonia, hydrogen) allowed for the creation of organic molecules.

    • Alternative Theories: Life could have originated at hydrothermal vents or via meteorite impact.

The Fossil Record

  • Formation of Fossils: Fossils typically form in sedimentary rocks, preserved in layers (strata); deeper layers are older.

  • Dating Fossils: Utilizes radiometric dating techniques, like Carbon-14 (5730 years half-life).

  • Insight from Fossils:

    • Tracks evolution, adaptations (e.g., flight), and impact of mass extinctions on biodiversity.

Major Events in Life's History

  1. Appearance of Prokaryotes:

    • Earliest evidence around 3.5 billion years ago (e.g., stromatolites).

  2. Eukaryotic Evolution:

    • More complex cells believed to have arisen via endosymbiosis, where one cell engulfs another, leading to mitochondria and chloroplasts.

  3. Colonization of Land: Complex life adapted to terrestrial living around 500 million years ago.

  4. Mass Extinctions: Significant loss of biodiversity and subsequent adaptations, including five known major extinctions.

Example of Mass Extinctions

  • Permian Extinction: 252 million years ago; wiped out 96% of marine species.

  • Cretaceous Extinction: 66 million years ago; responsible for the extinction of dinosaurs and significant marine life.

Adaptive Radiations

  • Post-extinction periods saw the emergence of new species that adapted to fill ecological roles formerly held by extinct groups.