Origin of Life Theories

Alexander Oparin's Primordial Soup Theory

• Early Earth's atmosphere was very reactive.
• Included lightning and high levels of ultraviolet rays.
• Chemical compounds in the primordial soup:
  • Hydrogen sulfide
  • Methane
  • Ammonia
  • Carbon dioxide
  • Phosphate
• Oxygen was absent.

Miller-Urey Experiment

• Conducted by Stanley Miller and Harold Urey.
• Simulated early Earth conditions:
  • Flask with hydrogen, methane, ammonia, and water.
  • Electric sparks to simulate lightning.
• Resulted in accumulation of amino acids (building blocks of proteins).

Early Life Forms

• Microscopic cell-like structures appeared 200-300 million years after Earth cooled.
• Known as proteinoid microspheres, similar to bacteria.

Paleontology and Fossils

Definition

• Study of life's existence, origin, and extinction.
• Focus on past ecosystems and evolution via fossils.

Archaeopteryx

• Fossil from late Jurassic period.
• Evidence of dinosaur ancestry of birds.
• Features:
  • Sharp teeth
  • Tiny forelimbs with three claws
  • Long, bony tail
  • Head covered with scales

Geology and the History of Earth

Definition

• Study of life based on rock evidence.
• Focus on Earth's changes over time.

Geologic Time Scale

• Represents evolutionary time.

Eons

• Phanerozoic Eon: >500 million years ago
  • Organisms with skeletons or hard shells.
• Proterozoic Eon: 2.5 billion – 540 million years ago
  • First multicellular organisms, mass extinctions.
• Archaeozoic Eon: 3.9–2.5 billion years ago
  • First life-forms (single-celled organisms).
• Hadean Eon: 4.6–3.9 billion years ago
  • Earth's formation from dust and gases.
• Precambrian Time: Proterozoic, Archaeozoic, and Hadean
  • Accounts for 90% of Earth’s history.

Eras of the Phanerozoic Eon

1. Paleozoic Era: 540–250 million years ago
   • Marine organisms, fish, amphibians, early reptiles.
2. Mesozoic Era: 250–65 million years ago
   • "Age of Reptiles/Dinosaurs," rise of flowering plants.
3. Cenozoic Era: 65 million years ago – present
   • "Age of Mammals," human civilization.

Periods

• Cambrian: First hard-shelled organisms.
• Ordovician & Silurian: First vertebrates and insects.
• Devonian: "Age of Fishes," first amphibians.
• Carboniferous & Permian: First reptiles.
• Triassic, Jurassic, & Cretaceous: Dinosaurs thrived, later extinct.
• Tertiary & Quaternary: Evolution of mammals, rise of humans.

Epochs

• Finer time subdivisions, applicable to recent periods.

Evolutionary Theories

Evolution

• Scientific explanation of life's diversity.
• Present-day organisms descended from ancient ones.

Theory

• Well-supported, testable explanation of natural phenomena.

Fitness and Natural Selection

• Fitness: Individual’s survival and reproduction ability in an environment.
• Natural selection: Individuals with advantageous traits survive and reproduce.

Evidence for Evolution

1. Fossil Records
   • Show organism changes over time.
   • Evidence for common ancestry.
2. Comparative Anatomy
   • Similar structures suggest shared evolutionary history.
3. Comparative Embryology
   • Similar embryonic development patterns indicate common ancestry.
4. Molecular Biology
   • DNA and protein sequence similarities show species relationships.

Example

• Dodo: Extinct due to overhunting and habitat destruction.
  • Highlights environmental impact on species survival.

Natural Selection and Genetics

• Artificial Selection: Human breeding for traits (e.g., dog breeds, crops).
• Natural Selection: Organisms with beneficial traits pass them to offspring.
• Genetic Drift: Random allele frequency changes due to chance.
• Mutation: DNA changes introducing new traits.
• Recombination: Genetic material mixing during reproduction, increases diversity.

Key Takeaways

• Life history is divided into eons, eras, periods, and epochs to study evolution.
• Theories like Oparin’s, Miller-Urey’s Experiment, and Darwin’s Natural Selection explain life's evolution.
• Fossils, anatomy, embryology, and molecular biology are evidence for evolution.
• Natural selection and genetic mechanisms drive population changes over generations.
• Understanding evolution and origin of biodiversity aids in tracing life development and species adaptation.