Chapter 25 PowerPoint

Chapter Overview

• Title: The History of Life on Earth

• Course: LSU BIOL 1202 General Biology II Lecture

• Instructor: Dr. Adam Hrincevich

Learning Objectives

1. Origin of simple cells from nonliving materials.

2. Define fossils, dating techniques, and significance of fossil records.

3. Timeline for origin of unicellular and multicellular organisms and land colonization.

4. Impact of plate tectonics, mass extinctions, and adaptive radiations on life.

5. Genetic changes leading to significant body form modifications.

6. Examples of how structures evolve through descent with modification.

Concept 25.1: Origin of Life

• Conditions on early Earth facilitated life:

  • Abiotic synthesis of organic molecules.

  • Formation of macromolecules.

  • Formation of protocells.

  • Emergence of self-replicating molecules.

Synthesis of Organic Compounds

• 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).

Protocells

• 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.

Self-Replicating RNA

• 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.

Concept 25.2: Fossil Record

• 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.

Dating Fossils

• 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.

Concept 25.3: Key Evolutionary Events

• Geologic record includes:

  • Eons: Hadean, Archaean, Proterozoic, Phanerozoic.

  • Major events: emergence of unicellular and multicellular life, land colonization.

Colonization of Land

• Fungi, plants, and animals began land colonization ~500 million years ago.

• Key adaptations: vascular systems in plants for moisture retention.

Concept 25.4: Speciation and Extinction

• 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).

Concept 25.5: Developmental Gene Changes

• Evolutionary changes in organisms arise from shifts in developmental gene regulation.

• Example: Heterochrony in skull formation in species.

Concept 25.6: Evolutionary Processes

• 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.

Major Biological Milestones

• 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.