Introduction to Geology

• Geology, also known as geoscience or Earth science, is a natural science that studies the Earth.
• The word "Geology" comes from the Greek words "geo" (earth) and "logos" (study of or science of).
• Geology is the primary Earth science, exploring Earth's formation, structure, composition, evolution, and dynamics, including its mineral and energy resources.

General Geology

• General geology studies the Earth's composition, structure, processes, and history.
• This field also examines minerals, fossils, groundwater, and the interactions between the Earth's surface and its deeper layers.

Roles of Civil Engineers in Geology

• Site Investigation and Geotechnical Assessment
• Foundation and Structural Stability Design
• Landslide Prevention and Slope Stabilization
• Seismic Risk Analysis and Earthquake-Resistant Design
• Groundwater and Environmental Management

Branches of Geology

• Physical Geology focuses on understanding Earth’s materials (rocks, minerals, and soils) and the physical processes that shape its surface.
• Historical Geology studies the history of Earth, using rock formations and fossils to understand its past.
• Mineralogy examines the properties, classification, and formation of minerals, the building blocks of rocks.
• Petrology focuses on the study of rocks, particularly their origin, formation, composition, and classification.
• Stratigraphy studies rock layers and their arrangement in time and space to interpret Earth’s history.
• Sedimentology focuses on the study of sediments (e.g., sand, clay) and the processes that form sedimentary rocks.
• Structural Geology examines how rocks deform under stress, forming geological structures such as faults, folds, and joints.
• Geophysics uses physical principles to study Earth’s interior and its physical properties (e.g., magnetic, gravitational, seismic).
• Paleontology studies fossils to understand the history of life and past environments on Earth.
• Geochemistry analyzes the chemical composition of Earth materials and the processes shaping Earth's systems.
• Hydrogeology focuses on groundwater distribution, movement, and quality, and its interaction with geological formations.
• Volcanology studies volcanoes, volcanic processes, and associated hazards.
• Geomorphology examines landforms and the processes that create and modify them (e.g., erosion, weathering, tectonics).
• Glaciology studies glaciers and ice sheets, their movement, and their effects on landforms and sea level.

Earth's Compositional Layers

• Crust – The outermost layer, composed mostly of oxygen, silicon, aluminum, iron, calcium, sodium, and potassium.
• Mantle – Located beneath the crust, it's composed of silicate minerals like olivine and pyroxene.
  • The upper mantle is rich in these minerals.
  • The lower mantle contains denser materials like perovskite.
• Core – The inner part of Earth, composed mainly of iron (85%) and nickel (10%), with some sulfur and oxygen.

Crust

• The crust is the outermost layer of Earth.
• It is a cold, thin, and brittle outer shell made of rock and makes up 1% of Earth's mass.

Oceanic Crust

• Composed of basalt lava flows and gabbro.
• Thickness: ~5–10 km
• Density: ~3.0 g/cm³

Continental Crust

• Composed of igneous, metamorphic, and sedimentary rocks.
• Thickness: 30–50 km
• Density: ~2.7 g/cm³

Mantle

• Composed of solid rock, hot and representing about 68% of Earth's mass.
• Extends approximately 2,900 km deep.

Core

• Mostly iron, making up about 31% of Earth.
• Radius of about 1,220 km.

Outer Core

• Liquid with a thickness of ~2,400 km.
• Composed mostly of nickel and iron.
• Density: 9.9–12.2 g/cm³

Inner Core

• Solid state.
• The transition between inner and outer core is at 5,150 km depth.
• Center temperature: ~5,500°C
• Highest density: 12.9 g/cm³

Divisions Based on Mechanical Properties

• Lithosphere – Rigid outer layer composed of the crust and upper mantle.
• Asthenosphere – Partially molten upper mantle that behaves plastically and can flow.

Processes That Shape Earth’s Structure and Composition

• Plate Tectonics
• Volcanism
• Erosion and Weathering
• Sedimentation
• Earthquakes
• Metamorphism
• Differentiation

Alfred Wegener & The Theory of Continental Drift

• Alfred Wegener (1880-1930) proposed the Theory of Continental Drift.
• The theory suggests that Earth's continents were once part of a supercontinent called Pangaea, which later broke into Laurasia and Gondwanaland.

Evidence for Continental Drift

• Apparent Fit of the Continents – Continents appear to fit together like puzzle pieces.
• Rock and Mountain Correlation – Identical rock formations and mountain structures exist on different continents.
• Fossil Correlation – Identical fossils are found on continents separated by oceans.
• Paleoclimate Data – Coal in cold regions and glacial evidence in warm regions indicate past climate shifts.

Plate Tectonics

• Plate tectonics explains how Earth's major landforms are created through the movement of its crust.

Types of Tectonic Plates

• Oceanic Plates – Thinner, denser, found beneath oceans.
• Continental Plates – Thicker, less dense, make up Earth's landmasses.

Major Tectonic Plates

• Eurasian Plate
• North American Plate
• Indo-Australian Plate
• Pacific Plate
• South American Plate
• African Plate
• Antarctic Plate

Types of Plate Boundaries

• Divergent – Plates move apart, forming rift valleys.
• Convergent – Plates collide, forming mountains or subduction zones.
• Transform – Plates slide past each other, causing earthquakes.

Major Earth Processes

• Plate Tectonics
  • Divergent Boundaries
  • Convergent Boundaries
  • Transform Boundaries
• Volcanism
  • Shield Volcanoes
  • Composite Volcanoes
  • Cinder Cone Volcanoes
• Earthquakes
  • Epicenter
  • Focus
  • Seismic Waves
• Weathering
  • Physical Weathering
  • Chemical Weathering
  • Biological Weathering
• Erosion
  • Water Erosion
  • Wind Erosion
  • Ice Erosion
  • Gravity Erosion
• Mass Wasting
  • Landslides
  • Mudflows
  • Rockfalls
  • Creep
• Deposition & Sedimentation
  • River Deposition
  • Glacial Deposition
  • Coastal Deposition
  • Aeolian Deposition
• Hydrological Cycle
  • Evaporation
  • Condensation
  • Precipitation
  • Infiltration
  • Runoff

Human Impact on Earth Processes: Impact of Earthquakes on Groundwater

• Crustal Deformation – Alters aquifer structures
• Liquefaction – Causes soil to behave like a liquid
• Water Quality Changes – Increases sediment and contamination

Impact on Civil Engineering Structures

• Building Foundations – Can fail due to soil instability
• Pipelines & Utilities – Corrosion and displacement risks
• Bridges & Roads – Altered water tables affect load-bearing capacity