Lecture_Exam_2__Stratigraphy__Early_Atmosphere__and_Paleozoic

Early Hypotheses on Earth's Formation

• Theories on Earth's surface formation have evolved over time.

• Neptunism:

  • Proposed by Abraham Werner.

  • Suggested all rocks precipitated from a primordial ocean.

  • Imagery of Earth covered by water, but lacked evidence.

• Catastrophism:

  • Championed by Baron George Cuvier.

  • Major geological features formed from sudden, violent events.

  • Did not match observations from geological fieldwork.

• Importance of evidence in scientific theories.

The Father of Historical Geology: James Hutton

• Introduced the concept of Uniformitarianism.

  • States that current geological processes (erosion, deposition) operated similarly throughout Earth's history.

  • "The present is the key to understanding the past."

  • Fundamental principle of geology.

Stratigraphy: Understanding Earth's History

• Stratigraphy: Study of rock layers (strata) and their sequence.

  • Each layer represents different periods of time like chapters in a book.

  • Contacts: Boundaries between layers serve as timestamps.

• Rock layers not always perfectly stacked; gaps called unconformities are common:

  • Indicate periods of erosion or missing rock deposits.

  • Present geological mysteries to solve.

Lateral Changes in Rock Layers

• Rock layers can change laterally, for example:

  • River deposits different sediments at varying distances from the mouth.

  • Sediment type informs about past environments (depth, energy, life forms).

• Transgressions and Regressions:

  • Transgressions: Sea level rises, shoreline moves inland.

  • Regressions: Sea level falls, shoreline shifts seaward.

  • Recorded in rock layers reflecting environmental changes.

Significant Role of Fossils in Geology

• Biostratigraphy: Using fossils to determine the age and relationships of rock layers.

  • Pioneered by William Smith (Strata Smith).

  • Recognized unique fossil assemblages in distinct layers for correlation across distances.

The Early Atmosphere of Earth

• During the Archean Eon:

  • The atmosphere was primarily hydrogen and helium, thin and lacking oxygen.

  • Changed through:

    • Photochemical Dissociation: Sunlight breaking down water vapor, producing oxygen.

    • Photosynthesis: Produced by early organisms, leading to oxygen buildup.

  • Ozone layer formation protected against UV radiation.

Emergence of Life

• Eerie Miller Experiment:

  • Simulated early Earth conditions; resulted in creating amino acids, building blocks of life.

  • Did not create life but suggested pathways for life development.

• Stromatolites:

  • Fossils of layered structures formed by cyanobacteria.

  • Existed over 3 billion years ago, released oxygen into the atmosphere.

Geological Changes During Early Earth History

• Massive volcanic activity and formation of first continents.

• Pioneering the presence of plate tectonics leading to geological upheaval.

Advancements into the Proterozoic and Paleozoic Eras

• Transition from single-celled to multicellular life.

• Paleozoic Era (540 to 250 million years ago): Explosion of life in oceans.

  • Eperek Seas: Shallow seas that provided rich environments for diverse life.

  • Continental collisions led to mountain ranges like the Appalachians.

Geological Tools and Techniques

• Paleomagnetism: Helps track continental movements by analyzing ancient magnetic fields in rocks.

• Biogeography: Studies fossil distribution to map ancient land connections.

Cratonic Sequences and Sea Level Changes

• North America's geological history characterized by sequences of transgressions and regressions, identified by geologist Lawrence Sloss.

• Example: Sauk Sequence: First major transgression, leading to sediment deposition from sandstones to limestones.

• Absaroka Sequence: Shift towards land-based environments, leading to coal formation in ancient swamps.

The Assembly of Pangaea

• Formation significantly altered climate, ocean currents, and life evolution.

• Massive mountain ranges formed during continental collisions influenced both land and oceanic life.

The Paleozoic Extinction Events

• Permian-Triassic Extinction: Most severe extinction event with around 90% marine and 70% terrestrial species lost.

  • Likely caused by massive volcanic eruptions leading to drastic climate changes and ocean acidification.

Conclusion

• The Paleozoic Era serves as a critical chapter in Earth's dynamic history: geological transformations, life diversification, and extinction events that shaped our planet.

• Understanding these historical processes highlights the interconnectedness of geological and biological evolution.