GEO1110 - Exam 1
Earth Sciences - GEO 1110/GE1150
Lecture 9 - Review for Test
Overview of Geology Courses
GE1150 & GEOL1110:
Physical Geology:
Examines the materials composing Earth.
Seeks to understand processes operating beneath and on Earth's surface.
Historical Geology:
Attempts to understand Earth’s origin and its development through time.
Establishes a chronological arrangement of changes in Earth’s geologic past.
Development of Geology as a Discipline
Catastrophism (Mid 1600s, James Ussher):
Suggested landscapes are shaped primarily by disasters.
Uniformitarianism (1795, James Hutton):
Modern geology was born here; states that laws of nature today have always applied.
Introduced the idea that "the present is the key to the past."
Does not imply uniform rates or relative importance in geological processes.
Nature of Scientific Inquiry
Science involves careful observations and explanations to understand nature.
Hypothesis: A tentative, testable explanation.
Theory: A well-tested explanation accepted by the scientific community.
Scientific Method: The systematic process for research involving questions, data gathering, and hypothesis testing.
Earth as a System
Earth is composed of interacting parts forming a complex whole:
Atmosphere: Gaseous envelope surrounding Earth.
Hydrosphere: Global bodies of water, including oceans and freshwater.
Biosphere: All living organisms.
Geosphere: The solid Earth itself.
Our Solar System Overview
Inner Planets:
Mercury, Venus, Earth, and Mars.
Formed from metallic and rocky substances; characterized as terrestrial planets.
Outer Planets:
Jupiter, Saturn, Uranus, Neptune.
Formed from ices and gases.
Earth's Internal Structure
Layering by Chemical Composition:
Crust:
Thin, rocky outer layer (7-70 km thick).
Composed of basalt (oceanic crust) and granodiorite (continental crust).
Mantle:
Composed of peridotite; approximately 2900 km thick.
Core:
Iron-rich, consists of outer (liquid) and inner (solid) layers.
Zones Based on Physical Properties
Lithosphere: Rigid outer layer (crust + upper mantle).
Asthenosphere: Soft, weak layer beneath lithosphere.
Transition Zone: Sharp increase in density below the asthenosphere.
Lower Mantle: Strong, hot rock subjected to gradual flow.
Outer Core: Liquid outer layer.
Inner Core: Solid inner layer.
Continental Drift Hypothesis
Alfred Wegener (1915):
Proposed that all landmasses once formed the supercontinent Pangaea.
It began fragmenting about 200 million years ago, resulting in current land positions.
Theory of Plate Tectonics
Developed post-World War II from oceanographic studies:
Key Findings:
New evidence of oceanic ridge systems.
No oceanic crust older than 180 million years.
Thin sediment accumulation in deep oceans.
Established theory explaining the interactions of tectonic plates.
Types of Plate Boundaries
Divergent Boundaries: Plates move apart, creating new seafloor.
Convergent Boundaries: Plates move toward each other, forming mountain belts or recycling oceanic lithosphere.
Transform Boundaries: Plates grind past one another without lithosphere production or destruction.
Age of Ocean Floor and Seafloor Spreading
Evidence amassed through deep-sea drilling indicates the ocean floor is youngest at ridge axes.
Fossil remains used for dating show sediment age increases with distance from ridges.
Minerals: Building Blocks of Rocks
Geologic Definition of a Mineral:
Naturally occurring, solid, crystalline, inorganic substance with a specific chemical composition.
Definition of a Rock:
A solid mass of minerals or mineral-like matter occurring naturally.
Rocks vs. Minerals:
Rocks are composed of one or more minerals, lacking a specific chemical composition.
How Do Minerals Form?
Processes:
Precipitation: Solids fall out of solution (e.g., evaporate deposits).
Crystallization: Occurs when magma cools and solidifies.
Deposition: Biological processes transform dissolved materials into minerals (e.g., coral reefs).
Abundant Elements in Continental Crust
Eight elements account for over 98% of continental crust weight:
Oxygen, Silicon, Aluminum, Iron, Calcium, Sodium, Potassium, Magnesium.
Rock-Forming Minerals
Over 800 known silicate minerals.
Silicates (90% of Earth's crust).
Important non-silicate minerals: Carbonates, Oxides, Sulfates, Halides.
Rocks and the Rock Cycle
Three Major Groups:
Igneous, sedimentary, and metamorphic.
The Rock Cycle:
Explains geological processes forming each rock type from the others.
Visualizes interrelationships among Earth system components.
Magma and Igneous Rocks
Magma: Molten rock located at depth.
Lava: Molten material surfacing.
Characteristics of Magma: Parent material for igneous rocks, forms by partial melting in Earth's crust and upper mantle.
Types of Igneous Rock:
Intrusive Igneous Rock: Crystallizes at depth (e.g., granite).
Extrusive Igneous Rock: Forms at the surface from lava.
Compositional Differences in Igneous Rocks
Classifications include:
Felsic: Light-colored, high silica (e.g., granite).
Intermediate: Between felsic and mafic (e.g., diorite).
Mafic: Dark-colored, lower silica (e.g., basalt).
Ultramafic: Very low silica, high magnesium and iron content.
Silica Content and Magma Behavior
Silica content affects magma viscosity and eruption temperature:
Granitic Magma: High silica, viscous, erupts at lower temperatures.
Basaltic Magma: Low silica, fluid, erupts at higher temperatures.
Igneous Textures
Texture denotes a rock's appearance based on mineral grain size and shape.
Influenced by:
Rate of cooling (slow = large crystals; fast = small crystals).
Amount of silica and dissolved gases.
Generating Magma from Solid Rock
Processes Leading to Magma Generation:
Decrease in Pressure: Reduces melting points (decompression melting).
Addition of Water: Lowers melting points.
Increase in Temperature.