BIOL_108_Wi25_09_Origin_of_Life

Origin of Life Overview

Life on Earth shares a common biochemical and genetic foundation. Biological polymers: nucleic acids, proteins, lipids, polysaccharides. Key components include five nucleotide bases, 20 amino acids, fatty acids, glycerol, and various sugars.

Definition of Life

• Organization: Composed of one or more cells.

• Metabolism: Management of energy and materials through chemical reactions.

• Response to Stimuli: Changes in growth, reaction, or movement.

• Homeostasis: Maintenance of internal chemical/thermal consistency.

• Adaptation: Changes over time in accordance with environmental shifts.

• Reproduction: Ability to produce new individual organisms.

Major Events in Life's History

• 4.6 billion years ago: Formation of Earth.

• ~3.9 billion years ago: First life (replicating molecules).

• ~2.7 billion years ago: Oxygen starts to accumulate due to photosynthesis (cyanobacteria).

Geologic Record

• Divided into eons:

  • Archaean

  • Proterozoic

  • Phanerozoic (further divided into three eras: Paleozoic, Mesozoic, Cenozoic).

• Major geological boundaries correspond to mass extinction events.

Fossil Record

• Provides evidence of evolutionary history through preserved remains.

• Bias: The fossil record is biased and incomplete due to factors like burial processes, organism type, and sedimentation.

• Types of Fossils:

  • Molds: Impressions left by organisms.

  • Casts: Minerals fill molds to create a replica.

  • Replacement: Original tissues replaced by minerals.

  • Trace Fossils: Evidence of behavior such as tracks or feces.

  • Preserved Fossils: Retain organic material; examples include amber and frozen specimens.

• Dating Fossils:

  • Relative Dating: Order of fossils established based on strata (e.g., index fossils).

  • Absolute Dating: Uses radioactive decay (e.g., carbon-14, potassium-argon) to determine actual age.

Continental Drift

• Movement of tectonic plates influenced Earth's geography and climate, affecting biodiversity.

• Major supercontinents included Pangaea, Laurasia, and Gondwana.

Mass Extinctions

• Five Major Mass Extinctions:

  1. Ordovician

  2. Late Devonian

  3. Permian

  4. Late Triassic

  5. Cretaceous

• Impact and Causes:

  • Permian Mass Extinction: Over 60% of species extinct, linked to drastic environmental changes.

  • Cretaceous Mass Extinction: ~50% marine species extinct including non-avian dinosaurs, likely caused by an asteroid impact.

Adaptive Radiation

• Rapid evolution of new species following mass extinctions, leading to diversification.

• Examples: Diversification of mammals following the dinosaur extinction event.

Origin of Life: Hypothesized Sequence of Events

1. Abiotic synthesis of small organic molecules.

2. Polymerization of small organic molecules into larger organic polymers.

3. Formation of protocells capable of basic life functions.

4. Emergence of self-replicating molecules.

First Life

• Prokaryotes: First life forms, divided into two domains: bacteria and archaea.

• Stromatolites: Oldest fossilized prokaryotes.

• Great Oxygenation Event: Caused by cyanobacteria, significantly increased atmospheric oxygen.

Definitions

• Fossil: Preserved remains or traces of ancient organisms.

• Continental Drift: Movement of tectonic plates that results in the shifting of continents over geological time.

• Mass Extinction: A rapid decrease in the biodiversity on Earth, often linked to catastrophic events.

• Adaptive Radiation: The evolutionary diversification of a species into several forms adapted to different environments.

• Prokaryote: Microscopic single-celled organisms without a nucleus, including bacteria and archaea.