Geological Time Scale

• Phanerozoic Eon (Visible Life)
  • Divided into three eras: Paleozoic, Mesozoic, Cenozoic
  • Significant mass extinctions occurred at the end of the Paleozoic and Mesozoic eras.

Eras and Their Diagnostic Groups

• Paleozoic Era (541 to 252 million years ago)

  • Diagnostic group: Trilobites (especially prevalent in early Paleozoic)

• Mesozoic Era (252 to 66 million years ago)

  • Diagnostic group: Non-avian Dinosaurs (characterized by the amniote egg)

• Cenozoic Era (66 million years ago to present)

  • Diagnostic group: Horses and horse-like ancestors

Reading Assignments

• Chapter 3: What the Rocks Say: How Geology and Paleontology Reveal the History of Life

  • Sections to review:
  • 3.1 The Great Age-of-the-Earth Debate
  • 3.2 A Curious Lack of Radioactivity
  • 3.3 A Vast Museum
  • 3.4 Bringing Fossils to Life
  • 3.5 Traces of Vanished Biology

• Chapter 14: Macroevolution

  • Sections to emphasize:
  • 14.2 The Drivers of Macroevolution: Speciation and Extinction
  • 14.3 Charting Life’s Rises and Falls
  • 14.6 Adaptive Radiations
  • 14.8 Extinction Events

Key Definitions

• Eons:
  • Proterozoic, Phanerozoic
• Eras:
  • Paleozoic, Mesozoic, Cenozoic
• Key Innovation: Significant evolutionary changes that alter organism interactions.
• Mass Extinction: A rapid decrease in biodiversity on Earth.
• Adaptive Radiation: Rapid evolution of a new group of organisms to adapt to new ecological niches.

Geological Time Scale Overview

• Time is segmented into Eons, Eras, Periods, and Epochs.
• Eons:
  • Proterozoic (2.5 billion years ago) → Phanerozoic (541 million years ago to present).
• Eras within Phanerozoic:
  • Paleozoic Era: Includes periods such as Cambrian, Ordovician, Silurian, Devonian, Carboniferous, Permian.
  • Mesozoic Era: Includes periods such as Triassic, Jurassic, Cretaceous.
  • Cenozoic Era: Includes epochs such as Paleocene, Eocene, Oligocene, Miocene, Pliocene, Pleistocene, Holocene.

Significant Fossil Records and Events

• The Cambrian Explosion witnessed a rapid diversification of life forms (541 mya).
• Mass extinction events led to adaptive radiations, where new groups (like mammals) diversified after events that wiped out existing dominant forms (like dinosaurs).
  • Examples of adaptive radiation include:
  • Cambrian radiation of animals due to environmental change and key innovations.
  • Cretaceous radiation of angiosperms facilitated by the evolution of flowers.

Extinctions and Diversification

• Mass Extinctions and Their Causes:
  • Background extinction rates vs. mass extinction events.
  • Extinctions can be caused by environmental changes (e.g. volcanic eruptions, asteroid impacts).
• Speciation vs. Extinction: The balance between species origination and extinction dictates overall species diversity.

Summary of Phanerozoic Eon

• Diagnostic fossils:
  • Paleozoic: Trilobites (indicative of the time).
  • Mesozoic: Non-avian dinosaurs, showcasing evolutionary adaptations.
  • Cenozoic: Horses, reflecting the evolution of modern biodiversity.
• Key Innovations led to dramatic evolution and diversification rates, emphasizing the interplay of different ecological dynamics over time.