Lecture 8 Slides

Lecture Overview

• Lecture Title: Patterns & Processes in Life History

• Instructor: Ray Troll

Lecture Objectives

By the end of this lecture, you should be able to:

• Summarize conditions on early Earth that made the origin of life possible.

• Explain how the fossil record documents the history of life.

• Recall key events in life’s history: origins of unicellular and multicellular organisms, colonization of land.

• Explain how the rise and fall of organisms reflect differences in rates of speciation and extinction.

• Describe mass extinctions and the resulting adaptive radiations.

• Note: Key terms are bolded for emphasis!

Part 1: Conditions on Early Earth

• Focuses on the environmental conditions conducive to the origin of life.

Key Events in Life’s History

• Single-celled organisms: The first form of life.

• Photosynthesis: Its evolution significantly impacted atmospheric conditions.

• Eukaryotes: The first eukaryotic cells appeared.

• Multicellularity: The emergence of multicellular organisms marked evolutionary progress.

• Settlement of Land: Organisms began to inhabit terrestrial environments.

• Timeline correlates these events with geological periods.

The Origin of Life

• Hypothesized four steps leading to life:

  1. Abiotic synthesis of organic molecules.

  2. Formation of organic polymers, consisting of repeating units.

  3. Formation of protocells, which are membrane-bound cell precursors.

  4. Formation of ribozymes, RNA-based catalysts facilitating biochemical reactions.

Early Atmosphere and Organic Molecules

• Early atmosphere was rich in organic molecules formed from simpler molecules.

• Energy from lightning and UV radiation facilitated chemical reactions.

• Resulted in a 'primordial soup' from which life eventually arose.

Miller-Urey Experiment

• Conducted in 1953 by Stanley Miller and Harold Urey.

• Simulated early Earth atmosphere and showed abiotic processes could create amino acids.

• Demonstrated that organic molecules could be produced from non-living materials under specific conditions.

Changes Since Life Began

• Fossil Record: Evidence of significant macroevolutionary changes over geological time.

  • Emergence of terrestrial vertebrates and photosynthesis are key milestones.

  • Mass extinctions have long-term impacts on life's evolution.

Fossil Record Limitations

• Limitations include:

  • Taxonomic bias (certain taxa are favored).

  • Habitat bias (some habitats are represented more than others).

  • Temporal bias (some time periods are over-represented).

  • Bias toward abundant species in fossil reviews.

Fossils and their Age

• Relative Age: Determined from their position in rock strata.

• Absolute Age: Determined via radiometric dating, tracking the decay of isotopes (e.g., C-14).

• Each isotope has a known half-life, allowing for calculation of age based on decay percentage.

Timeline of Life on Earth

• Cosmic Calendar: A visual representation of life's history divided over a year:

  • Major events are highlighted by month.

  • This facilitates understanding of Earth’s 13.8 billion year history in a simplified manner.

• Key events include:

  • Formation of supercontinents.

  • Evolution of vertebrates and land plants.

  • Extinction events marking significant geological epochs.

Geological Eons

• Eons Information:

  • Hadean, Archaean, Proterozoic, and Phanerozoic labeled as major timeframes based on significant events like mass extinctions.

  • Total timeframes before the current eons encapsulate roughly 4 billion years.

Mass Extinctions

• Major extinctions: Permian (96% of species disappeared) & Cretaceous (75% of species, including non-avian dinosaurs).

• These events lead to significant shifts in biodiversity and paved the way for adaptive radiations in different ecological niches.

Adaptive Radiation

• Occurs when organisms diversify from a common ancestor into new forms.

• Notable examples:

  • Mammals radiating after the extinction of dinosaurs.

  • Colonization of land plants, insects, and tetrapods.

Summary: The Rise and Fall of Species

• Changes over time documented by the fossil record, showcasing both extinction events and the emergence of new species.

• Adaptive radiations occur following extinctions, indicating ongoing evolutionary processes.

Presentation and Engagement

• Encouragement for questions and clarification throughout the lecture series.