Title: The History of Life on Earth
Course: LSU BIOL 1202 General Biology II Lecture
Instructor: Dr. Adam Hrincevich
Origin of simple cells from nonliving materials.
Define fossils, dating techniques, and significance of fossil records.
Timeline for origin of unicellular and multicellular organisms and land colonization.
Impact of plate tectonics, mass extinctions, and adaptive radiations on life.
Genetic changes leading to significant body form modifications.
Examples of how structures evolve through descent with modification.
Conditions on early Earth facilitated life:
Abiotic synthesis of organic molecules.
Formation of macromolecules.
Formation of protocells.
Emergence of self-replicating molecules.
Earth formed 4.6 billion years ago (BYA).
Early atmosphere lacked oxygen; consisted mainly of water vapor and volcanic gases (e.g., nitrogen, methane).
Theories by Oparin & Haldane, validated by Miller-Urey experiments demonstrating abiotic synthesis in a reducing atmosphere.
Organic compounds also produced near hydrothermal vents and from meteorites (e.g., Murchison meteorite).
Early life properties possibly arose together:
Protocells formed from vesicles with membranes.
Lipids and organic molecules spontaneously create vesicles.
Protocells could replicate and undergo metabolic processes.
RNA likely served as the first genetic material.
Ribozymes catalyze reactions and replicate RNA.
Successful RNA forms propagated through natural selection, potentially leading to DNA evolution.
Fossil record illustrates life's history:
Reveals changes and evidence of extinct organisms through sedimentary rock strata.
Bias in fossilization based on species' longevity, abundance, and structure.
Relative dating through strata order; radiometric dating for actual ages (e.g., C-14 dating).
Long-lived isotopes for older fossils; cycling isotopes in sediment to estimate ages.
Geologic record includes:
Eons: Hadean, Archaean, Proterozoic, Phanerozoic.
Major events: emergence of unicellular and multicellular life, land colonization.
Fungi, plants, and animals began land colonization ~500 million years ago.
Key adaptations: vascular systems in plants for moisture retention.
Life's history characterized by rise and fall of organisms influenced by speciation and extinction rates.
Mass extinction events have historically impacted biodiversity (e.g., Permian and Cretaceous extinctions).
Evolutionary changes in organisms arise from shifts in developmental gene regulation.
Example: Heterochrony in skull formation in species.
Evolution is not goal-oriented but a series of modifications from existing structures (e.g., eye evolution).
Exaptations arise when structures transition to new functions over time.
3.5 BYA: First prokaryotes.
1.8 BYA: First eukaryotes.
500 MYA: Colonization of land.
1.2 BYA: First multicellular eukaryotes.
535-525 MYA: Cambrian explosion, marked by diversification of animal forms.