Geologic Concepts

MAJOR SUBDIVISIONS OF GEOLOGIC TIME: Geologic Time Scale- A record of Earth’s history, beginning 4.6 billion years ago, that shows events time units, and history. MAJOR SUBDIVISIONS OF GEOLOGIC TIME: Eras- based on differences in life-forms. Example: Mesozoic Era is ended by the marked extinction of dinosaurs and many other organisms about 66 million years ago. Periods- based on the types of life existing at the time and on geologic events Epochs- subdivisions of periods. Only the Cenozoic Era is subdivided further into epochs.

The Earth Is a Dynamic Planet Geology: study of dynamic processes taking place on earth’s surface and in earth’s interior Three major concentric zones of the earth Core (inner-solid metal & outer- molten metal) Mantle (rocky & upper: asthenosphere-molten) Crust Continental crust Oceanic crust: 71% of crust Figure 14-3: The earth is composed of a core, mantle, and crust, and within the core and mantle, dynamic forces have major effects on what happens in the crust and on the surface.

The Earth Beneath Your Feet Is Moving The earth’s crust is broken into tectonic plates “Float” on the asthenosphere Much geological activity takes place at the plate boundaries Figure 14-18: The earth’s crust has been fractured into several major tectonic plates. White arrows indicate examples of where plates are colliding, separating, or grinding along against each other in opposite directions.

The Earth Beneath Your Feet is Moving Plate tectonics Theory explaining the movement of tectonic plates and the processes that occur at their boundaries More commonly referred to as “continental drift” theory Plates slide across surface of earth and can break or collide Plate boundary = area where 2 plates meet

The Earth Beneath Your Feet is Moving Convection currents cause plate tectonics Move 2-15 cm per year

The Three Types of Plate Boundaries: Divergent Two plates move apart as magma (liquid rock) rises upward to create new lithosphere “Seafloor spreading”: new curst on ocean’s bottom & subduction of heavier oceanic plates beneath less dense continental plates

The Three Types of Plate Boundaries: Divergent Example: Mid- Atlantic Ridge/Iceland Giant undersea mountain range Formed 20 million years ago as Africa & South America separated

The Three Types of Plate Boundaries: Convergent Where plates meet: Oceanic & continental Continental & continental Oceanic & Oceanic “Subduction zone”-One plate is subducted (sideways and downward under) another Tends to lead to mountain ranges and volcanoes Ex. Andes Mountains, Marianas Trench in ocean

The Three Types of Plate Boundaries: Transform Where plates slide past each other Most famous example: The San Andreas Fault in California

Volcanoes Release Molten Rock from the Earth’s Interior Magma rising through the lithosphere reaches the earth’s surface through a crack Eruption – release of lava, hot ash, and gases into the environment, determines shape of volcano Form at divergent plate boundaries, subduction zones & over hot spots

Types of Volcanoes Cinder cone Shield cone Steep cones Wider bases From violent eruptions Shield cone Wider bases From quiet eruptions

Types of Volcanoes Composite Cones Hotpots From alternating eruptions Chains of volcanoes that form when mantle pass over a relatively small, long- lasting, hot region Examples: Hawaiian/ Galapagos Islands

The Ring of Fire Lots of volcanoes and earthquakes Very active plate boundaries

Earthquakes Are Geological Rock-and-Roll Events Breakage and shifting of rocks At a fault Seismic waves Vibrations in the crust Focus – origin of earthquake Magnitude – severity of earthquake Amplitude – size of the seismic waves Primary effects: shaking Secondary effects: rockslides, fires, flooding, tsunamis Figure 14-19: The San Andreas Fault, created by the North American Plate and the Pacific Plate sliding very slowly past each other, runs almost the full length of California (see map). It is responsible for earthquakes of various magnitudes, which have caused rifts on the land surface in some areas (photo).

Earthquakes Are Geological Rock-and-Roll Events Elastic Rebound Theory: When a fault is locked, stress builds up until rocks fracture Move & return close to their original locations Movement creates waves in rocks

Seismic Waves P-waves (Primary waves) Fastest Travel through solid/liquids Compression waves (push-pull) S-waves (Secondary waves) only through solids Side to side wave (sine wave) L-waves (Surface waves) Only on the surface Up and down

Liquefaction of recent sediments causes buildings to sink Two adjoining plates move laterally along the fault line Earth movements cause flooding in low-lying areas Landslides may occur on hilly ground Figure 14-21: An earthquake (left) is one of nature’s most powerful events. The photo shows damage from a 2010 earthquake in Port-au-Prince, Haiti. Shock waves Focus Epicenter Fig. 14-21, p. 367

Earthquakes Are Geological Rock-and-Roll Events Richter scale Insignificant: <4.0 Minor: 4.0–4.9 Damaging: 5.0–5.9 Destructive: 6.0–6.9 Major: 7.0–7.9 Great: >8.0 Largest recorded: 9.5 in Chile, 1960

Earthquakes on the Ocean Floor Can Cause Huge Waves Called Tsunamis Series of huge waves generated when ocean floor suddenly rises or drops Travels several hundred miles per hour Figure 14-22: This diagram illustrates how a tsunami forms. The map shows the area affected by a large tsunami in December 2004—one of the largest ever recorded.

Earthquakes on the Ocean Floor Can Cause Huge Waves Called Tsunamis 2011 – Japan tsunami Damaged nuclear reactors Detection of tsunamis Buoys in open ocean December 2004 – Indian Ocean tsunami Magnitude 9.15 and 31-meter waves at shore