Geological Processes: Earth’s Formation, Evolution, and Plate Tectonics

Posted on Oct 27, 2024 in Geology

ITEM 11: Dorsal Features and Plate Tectonics

Dorsal Features

Dorsal: 2/3 km seamounts on abyssal plain.
Failure: Fractures displaced laterally.

Ages

  • Rocks on the ridges: Basalts 1 million years old.
  • Aging on separating the dorsal: Increased every time we parted dorsal.
  • Age-related power: Power and thickness increase away.

Lithosphere

The lithosphere is created at the ridges and spreads laterally. There are places where the lithosphere is reintroduced into the deep Earth (subduction zones). Volcanoes and earthquakes are not homogeneously distributed, but concentrated in certain geologically active areas. Seismic and volcanic zones are active, while others are very stable. There are places where large masses of materials are moved with respect to other lithospheric plates.

Lithospheric Plates

  • Border or plate boundary: A boundary between two plates.
  • Types:
    • Mid-ocean ridges: Generate new oceanic lithosphere.
    • Subduction zones: Destroy lithosphere.
    • Transform faults: Neither create nor destroy lithosphere.

Plates: Eurasian, African, Indo-Australian, Pacific, North American, South American, and Antarctic.

Convection Currents

Warm materials dilate, lose density, rise, cool down, and descend (convection currents) which move plates. These currents are driven by:

  • Deep Earth’s thermal energy.
  • Gravity (gravitational pull).

Formation of an Ocean

Lithosphere rises and bows > Formation of a rift > Formation of oceanic lithosphere > Formation of an ocean.
Current ocean examples: Great South Africa-Africa-Mar valleys of red-Atlantic Ocean.

Theory of Global Tectonics

  • Lithosphere: Divided into a rigid set of fragments called lithospheric plates.
  • Boundaries of lithospheric plates: May be of 3 types (dorsal, subduction, transform fault).
  • Oceanic lithosphere: Continually renewed.
  • Continental lithosphere: More permanent, moves over plastic mantle materials.
  • Lithospheric plate movements: Caused by thermal energy inside the Earth and gravity, leading to ever-changing positions.

ITEM 12: Deformation, Folds, and Faults

Types of Deformation

  • Elastic: Recovers its initial form (tension).
  • Plastic: Does not retrieve the original form (compression).
  • Rupture: Occurs under strong compression in rigid materials (break).

Strike and Dip

  • Strike: Horizontal angle, forming a layer contained in the north-south plane.
  • Dip: The angle between the surface layer and a horizontal plane.

Folds

  • Axial plane: A plane that divides the fold into two symmetrical halves.
  • Hinge: Area of maximum curvature of the fold.
  • Axis: Axial plane intersection with the ground.
  • Flank: Side of the fold.
  • Core: Interior of the fold.
  • Types:
    • Anticline: Core contains older materials.
    • Syncline: Core contains younger materials.
    • Recumbent: Axial plane at 90°.
    • Inclined: Axial plane between 85° and 10°.
    • Overturned: Axial plane within 10° of horizontal.
    • Inverted: Axial plane greater than 90°.
    • Symmetrical: Two symmetrical halves.
    • Asymmetrical: Two non-symmetrical halves.

Fold Associations

  • Anticlinorium: Characteristic shape of an anticline.
  • Synclinorium: Characteristic shape of a syncline.

Fractures

  • Joints: Fractures where blocks do not displace relative to each other, or if they do, they expand and open the crack further.
  • Faults: Fractures in which displacement has occurred in one block relative to another.
  • Fault plane: Surface of the fault.
  • Fault lips: Blocks divided by the fault (raised and sunk lips).
  • Fault displacement: The distance between the lips.
  • Fault direction: Direction and dip of the fault plane.
  • Types:
    • Normal/Direct: Fault plane dips toward the downthrown lip. Associated with areas of crustal extension.
    • Reverse: Fault plane dips toward the upthrown lip. Associated with areas of crustal shortening.
    • Strike-slip: Horizontal displacement.

Fault Associations

  • Graben: A downthrown block bounded by parallel normal faults.
  • Horst: An uplifted block bounded by parallel normal faults.

Mountain Formation

  1. Formation of the accretionary prism.
  2. Magmatism and metamorphism.
  3. Orogenic uplift (thickening of the continental crust) or isostatic uplift.

Continental Collision Process

  1. Oceanic subduction.
  2. Closure of the oceanic basin.
  3. Continental collision.

Processes in Continental Collision

  • Internal geological processes: Thermal energy, gravity.
  • External geological processes: Solar energy, gravity.

Mutual Influences

  • Internal processes influence external processes:
    • Elevation of a mountain range leads to active erosion, severe erosion in higher areas.
    • Displacement of a continent closer to or further from the equator causes climate change.
    • Volcanic activity modifies atmospheric composition and dynamics (climate change, erosion processes, and sediment transport).
  • External processes influence internal processes:
    • Removal and deposition of materials causes isostatic imbalances.
    • Provide sedimentary materials that will be folded and fractured during mountain building.
    • Water in subducted sediment promotes the melting of rocks (magmatic activity).

ITEM 13: Determining Geological History

How to Determine Geological History

  • Origin of materials: Volcanic eruptions, lava flows, ice.
  • Generating form: Erosion of a cliff creates an abrasion platform.
  • Resulting structure: Compressive folds or faults.

Dating Techniques

  • Relative dating: Establish the order of events (before and after).
  • Absolute dating: Determine the numerical age of an event.

Fundamentals of Dating

  • Original horizontality: Strata are originally horizontal; if they are vertical, it indicates deformation.
  • Superposition: Older strata are below younger strata.
  • Fossils: The presence of known fossils helps to order strata.
  • Grain size sorting: Sedimentation of materials by size.
  • Desiccation cracks: Indicate drying of clay sediments.

Fossil Significance

  • Past life: Fossils reveal unique organisms that inhabited the Earth.
  • Depositional environment: The environment in which the organism lived is the same as that of the rock.
  • Age of rock formation: Fossils can be used to determine the age of the rock.
  • Index fossils: Fossils that lived for a short period, had a wide geographical distribution, and are abundant in rocks.

Radioactive Decay

Parent element (1) decays into daughter element (2).
Half-life: Time it takes for half of the parent element to decay.

Geological Time

  • Unit of time: Millions of years (Ma).
  • Geological time: The period elapsed since the Earth was formed to the present.
  • Time divisions: Precambrian (Archean and Proterozoic) and Phanerozoic (Paleozoic, Mesozoic, and Cenozoic).

ITEM 14: Earth’s Origin, Life, and Climate Change

Origin of Earth

  1. Nebula of dust and gas concentrates.
  2. Gravitational attraction forms the protosun.
  3. The sun’s temperature increases, and particles form planetesimals around it.
  4. Collisions of planetesimals form protoplanets.
  5. Protoplanets incorporate planetesimals, leaving a clean orbit.

Birth of Earth

  • Heavy materials sink to the bottom (core).
  • Gases escape to the outside (atmosphere).
  • Medium density materials form the mantle.
  • Plenty of steam forms the oceans.

Early Atmosphere

  • Formation: Degassing from the planet’s interior.
  • Content: Large amounts of carbon dioxide and water vapor, nitrogen.
  • Currently: Contains more oxygen and ozone.

Origin of Life

  1. Formation of simple organic molecules: Solar radiation and electrical discharges.
  2. Formation of complex organic molecules: Simple molecules combine and accumulate in the ocean (primordial soup).
  3. Formation of coacervates: Primordial soup molecules join together and form coacervates. Within coacervates, cell doubling occurs.

Precambrian

  • Divisions: Archean and Proterozoic.
  • Formation of stromatolites: By cyanobacteria.
  • Other bacteria: Contributed oxygen to the atmosphere (photosynthetic activity) and withdrew large amounts of carbon dioxide from the atmosphere.
  • Origin of eukaryotic organisms: First eukaryotic organisms and Pangea.

Paleozoic

  • Ice age and diversification:
  • Events:
    • Pangea 2.
    • Cambrian explosion (large groups of animals).
    • Animals with shells.
    • Carboniferous (plants and carbon deposits).
    • Origin of vertebrates (marine, amphibians, reptiles).
    • Permian extinction (major extinction event).

Mesozoic (Age of Reptiles)

  • Origin of ammonites.
  • Maximum development of reptiles.
  • First mammals.
  • First birds.
  • Flowering plants.

Cenozoic (Age of Mammals)

  • Diversification of mammals and birds (exploiting ecological niches).
  • Diversification of flowering plants.
  • Uplift of large mountain ranges.
  • Appearance of hominids.

Hominids

  • Australopithecus: Short, small brain volume.
  • Homo habilis: Similar to Australopithecus but with increased brain volume.
  • Homo antecessor: More evolved, greater height and brain volume.
  • Homo neanderthalensis and Homo sapiens: Our recent ancestors.

Climate Changes

  • External causes: Changes in solar radiation or meteorite impacts.
  • Internal causes: Composition of the atmosphere, continental drift.
  • Most significant change: Introduction of oxygen into the atmosphere.

Glaciations

Changes in temperature leading to ice coverage.
Principal epoch: Quaternary (evolution of mammals).

Mass Extinctions

  • Definition: Short periods of time with large numbers of species extinctions.
  • Principal extinctions:
    • Paleozoic (80% of marine species, 70% of terrestrial species).
    • Mesozoic (dinosaur extinction and more than half of all species).

Global Warming

  • Causes: Deforestation, burning of fossil fuels.
  • Consequences: Temperature increase, biodiversity loss.