Intro Geology’s Three 9

Understanding Geology and Its Basic Assumptions

• Geology operates under the basic assumption of uniformitarianism.

  • Defined as the principle that the processes observed in the present also explain the past.

  • Disregards the concept of magic or supernatural explanations for geological phenomena.

• This assumption serves as a guiding principle for not only geology but other sciences as well.

Historical Context of Geological Models

• Until recently, geology lacked a comprehensive model to explain various phenomena, unlike other sciences that had developed significant frameworks:

  • Astronomy and Physics: In the 1600s, Newton established a predictive model called mechanics, based on gravitational forces.

  • Chemistry: By the 1700s, Lavoisier introduced the enduring concept of mass conservation, dismantling alchemical notions.

  • Biology: In 1859, Darwin's "Origin of Species" provided an evolutionary model for biological sciences.

• During the 1960s, geology made significant strides in developing a working model, particularly after the space missions aimed at lunar geology.

Rise of Plate Tectonics

• The field of geology transformed dramatically with the introduction of plate tectonics in the late 1960s, which provided an explanatory framework for many geological phenomena:

  • This model explains the distribution of earthquakes, volcanic activity, and mountain formations by focusing on the movements of tectonic plates.

  • Harry Hess’s contribution during this period, which highlighted seafloor spreading as a driving force behind plate movements, was pivotal.

Key Concepts of Plate Tectonics

• Lithosphere: The outer rigid portion of the Earth, divided into tectonic plates that move independently due to seafloor spreading.

• Types of Plate Boundaries:

  • Diverging Boundaries: Plates pull apart, resulting in volcanic activity and the creation of new rock.

    • Example: The Mid-Atlantic Ridge.

  • Converging Boundaries: Plates collide, leading to subduction, volcanic arcs, and significant earthquake risks.

    • Example: The Cascadian Volcanic Arc, Japanese volcanic arcs.

  • Transform Boundaries: Plates slide past each other, which can lead to lateral movement and earthquakes.

    • Example: The San Andreas Fault in California.

Implications of Plate Tectonics

• Plate tectonics provides a coherent explanation for why certain regions experience specific geological phenomena:

  • Earthquakes can be predicted based on the type of plate movements.

  • Regions on plate boundaries (like California or Japan) are at a higher risk of earthquakes.

• Understanding plate tectonics is crucial for assessing geological hazards and their potential impacts on infrastructure and human safety.