Chapter 4: Deep Time

1. What are the three main types of rocks, and which one contains fossils?

• Igneous: Formed from cooling magma (e.g., basalt, granite).

• Metamorphic: Formed by heat and pressure (e.g., marble, schist).

• Sedimentary: Formed from compressed sediments; most fossils are found in these rocks (e.g., limestone, shale).

2. What are Steno’s principles of stratigraphy?

• Superposition: Oldest layers are at the bottom.

• Original Horizontality: Rock layers start horizontal.

• Lateral Continuity: Layers extend sideways until interrupted.

• Cross-Cutting Relationships: Features cutting through layers (faults, intrusions) are younger than the layers they cut.

• Faunal Succession: Fossil species appear in a predictable order

3. What is deep time, and who discovered it?

• Deep time is the concept that Earth's history spans billions of years.

• James Hutton (1726–1797) introduced it based on slow geological processes (uniformitarianism).

4. How do we determine the age of fossils and rocks?

• Relative Dating: Uses rock layers and fossil succession.

• Radiometric Dating: Measures decay of radioactive isotopes (e.g., uranium-lead, carbon-14).

5. What is the estimated age of the Earth, and how was it determined?

• 4.55 billion years (Ga), determined using radiometric dating of meteorites.

6. What is half-life, and how does it relate to dating fossils?

• Half-life is the time it takes for half of a radioactive isotope to decay.

• Example: Uranium-238 has a half-life of 4.5 billion years and decays into lead-206.

7. What is the Phanerozoic Eon, and what are its three eras?

• Phanerozoic = "Visible Life" (541 Ma–present).

• Paleozoic (541–252 Ma): "Ancient life" – early fish, first reptiles.

• Mesozoic (252–66 Ma): "Age of Reptiles" – dinosaurs dominate.

• Cenozoic (66 Ma–present): "Age of Mammals" – humans appear.

8. What are the three major mass extinctions of the Mesozoic?

• Permian-Triassic (252 Ma): Largest extinction (96% of marine life lost).

• Triassic-Jurassic (201 Ma): Cleared way for dinosaurs to dominate.

• Cretaceous-Paleogene (66 Ma): Killed non-avian dinosaurs (asteroid impact).