Ch. 1 - Intro to Geology

Class: GEOL-101
Topics:
Date: 2025-08-26

Notes:

What do geologists do?

• Try to understand how various processes on Earth work.
• Apply this knowledge about Earth processes to answer questions and/or solve problems.

1.1 Geology: The Science of Earth

Distinguish between physical and historical geology and describe the connections between people and geology

Physical and Historical Geology

• Physical geology: Seeks to understand the many processes that operate beneath and on the surface of our planet.
  • Physical Geological Processes (e.g., Plate tectonics, volcanism, orogeny, etc.)
• Historical geology: Seeks to understand the origin of Earth and its development through time.
  • Historical Evolution of Earth Preserved in the Rock Record (Changes in Depositional Environments, Fossil Assemblages, Faulting, Volcanism)
  • Think of Paleontology, finding out age of things
  • Studying layers of rocks (there is a term for this)
  • Predict were we might found out natural resources

Geology, People, and the Environments

• Natural Hazards
  • Geologists study volcanoes, floods, tsunamis, earthquakes, and landslides.
  • These are natural processes but become hazards when they occur where people live.
  • More people now live in cities than in rural areas. Mega populations are more vulnerable to hazards.
  • e.g. 2011 Tōhoku Earthquake and Tsunami (19,759 Dead) Magnitude 9.0
  • Understand these natural processes and where these might affect people

Geology and Society

Geology is a science that explores many important relationships between people and the natural environment. Complicating all environmental issues is the rapid growth of world population.

Global Map of Earthquakes (2000-2008; > 5.0 M)
Do these earthquakes occur near mega population centers?

World population growth

• Resources are an essential focus of geology
• Resources include water and soil, various metallic and nonmetallic minerals, and energy (oil/natural gas).
  • e.g. potassium is important because we make fertilizers with it
  • There is Lithium in the Salt Lake at Utah
• Geology deals with maintaining resource supplies and the environmental impacts of their extraction and use.

Mineral resources represent an important link between people and geology

1.2 The Development of Geology

Summarize early and modern views on how change occurs on Earth and relate them to the prevailing ideas about the age of the Earth.

The nature of Earth has been a focus of study for centuries

Aristotle (384 – 322 B.C.E.)

• Aristotle's explanations, lacking observational or experimental support, perpetuated misconceptions about natural phenomena for centuries.
  • Very famous, smart guy, supported by many
  • Didn't know about plate tectonics
• It was not until the Renaissance that a renewed curiosity and commitment to evidence-based inquiry began advancing our understanding of Earth.

Catastrophism (Mid 1600s – James Ussher, Archbishop of Armagh)

• The Earth’s landscapes were shaped primarily by catastrophes.
  • Giant floods
  • Volcanism
• Ussher calculated that Earth was only a few thousand years old, created in 4004 B.C.E.
  • Quite different to modern measurements

Uniformitarianism (1795 – James Hutton)

• The physical, chemical, and biological laws that operate today have operated throughout the geologic past. “The present is the key to the past”
  • We consider him the father of Geology.
• Seemingly small forces can, over long periods, produce effects comparable to sudden catastrophic events.
  • We can have the same types of effects with small forces (e.g. Erosion - damage to plate tectonics)
• Demonstrated that many geologic processes must occur over extremely long periods and carefully cited verifiable observations to support his ideas.

Geology Today

• Uniformitarianism is still valid.
  • Some geologic processes are not directly observable
  • Well-established evidence to suggest they occur.
• Earth processes vary in intensity but take a long time to create or destroy major landscape features.
• The magnitude of geologic time involves millions and billions of years.
• Earth is 4.6 billion years old
  • Through various proxies, tools, and geological measurements that how we were able to measure the age of rocks which then gives us an estimate of the age of the Earth.

Geological Time Scale

• Chronological system that uses the rock record to represent time.
• Describe the timing and relationship of geologic events.
• Based on stratigraphy, fossils, mass extinctions
• Currently:
  • Phanerozoic Eon
  • Cenozoic Era
  • Quaternary Period
  • Holocene or Anthropocene Epoch (?)

• A combination of tens of thousands of geologists that studied different areas and rocks

1.3 The Nature of Scientific Inquiry

Discuss the nature of scientific inquiry, including the construction of hypotheses and the development of theories

• Science is a process of observing the natural world, identifying patterns, and asking testable questions.
• Scientists use data (measured evidence) to build explanations and make predictions about how Earth systems behave.
  • Quantitative approach to formulate hypothesis
• The guiding assumption: natural processes are consistent and predictable, allowing us to understand past, present, and future Earth events.

• Hypothesis: a testable, tentative explanation for an observation (e.g., “Volcanoes in the Pacific Ring of Fire are related to plate boundaries”).
  • Trying to falsify it
  • Example: Consider the Hawaiian islands, those are an exception to volcanoes in the Pacific Ring of Fire
• Theory: a well-tested, widely accepted explanation that unifies observations (e.g., Plate Tectonic Theory, supported by earthquakes, volcanoes, and seafloor spreading).
• A theory is not a guess—in science, it represents the strongest level of understanding supported by evidence.

1.4 Earth as a System

List and describe Earth’s four major spheres. Define system and explain why Earth is considered a system

Earth is a dynamic body with many separate, but interacting parts:

• Hydrosphere– global ocean and freshwater

  • 75% of the Earth's surface is water
  • 97% of that water is salt water
  • 3% is freshwater (2% is in ice and glaciers)

• Atmosphere– gaseous envelope that surrounds the Earth

• Geosphere– the solid Earth

• Biosphere– all plant and animal life

• A system is a group of interacting parts that form a complex whole.

  • Think of 'soil' it is kind of an interface where we have all 4 "spheres"

• Earth system science:

  • Aims to study Earth as a system composed of numerous interacting parts
  • Employs an interdisciplinary approach to solve global environmental problems

• Processes that characterize the Earth’s system vary on spatial and temporal scales and are powered by energy from the Sun and heat from the Earth’s interior.

  • Example: How does the Geosphere influence the Atmosphere?
    • Think of CO2 interactions
    • Magnetosphere created by the geosphere
      • Without a magnetosphere we would not have an atmosphere
  • Example: How is the heat generated by the earths interior?
    • Decay of radioactive elements
    • There is a temperature pressure component
      • Higher pression as you go deeper
    • Heat is distributed through radioactive decay

Earth Spheres

• Hydrosphere: Covers 71% of Earth’s surface, stores 97% of Earth’s water, and shapes landscapes through circulation in the water cycle.
  • Rain is part of the Hydrosphere
• Atmosphere: Provides air for life, shields Earth from harmful radiation, and drives weather and climate through energy exchanges.
• Biosphere: Encompasses all life, concentrated near Earth’s surface, and interacts with air, water, and land to sustain ecosystems.
• Geosphere: The solid Earth, extending from surface soils to the core, providing the foundation for landscapes and Earth processes.

Links between the Earth System

Biosphere ↔ Atmosphere: Plants absorb CO₂ during photosynthesis; animals and humans release CO₂ through respiration.

Geosphere ↔ Atmosphere: Volcanoes release carbon from Earth’s interior; fossil fuel combustion transfers carbon stored in rocks into the air.

Hydrosphere ↔ Atmosphere: Oceans absorb CO₂ from the air and release it
back, regulating climate.

Biosphere ↔ Geosphere: Decomposition of plants and animals stores carbon in soils and fossil fuels, linking life to long-term carbon reservoirs.

Carbon Cycle

• Carbon emitted

• Fossil fuels

• Anthropogenic fires

• Returns typically through plants and other processes

• A lot of elements have these complex cycles as well

1.5 Origin and Early Evolution of Earth

Outline the stages in the formation of our solar system

Origin of our Solar System

• The universe began with the Big Bang (13.8 billion years ago).
  • Hydrogen and Helium atoms distributed throughout the space
• The components of the solar system formed at essentially the same time out of the same material.
• The Nebular Theory proposes that the bodies of our solar system evolved from an enormous rotating cloud called the solar nebula. (cloud of hydrogen and helium atoms as well as microscopic dust grain)

• Terrestrial planets are closer to the Earth/sun
• Rocks and dust in the space colliding with each other forms a magma planet
• Outgassing of stage L forms our early atmosphere

Nebular Theory

• The solar nebula consisted of hydrogen, helium, and microscopic dust grains.
• A disturbance caused the solar nebula to slowly contract and rotate.
• The solar nebula assumed a flat, disk shape with the protosun (pre-Sun) at the center.
• Inner planets began to form from metallic and rocky substances.
• Larger outer planets began forming from fragments of ices (H2O, CO2, and others).

Inner and Outer Planets of the Solar System

• Inner planets (Mercury, Venus, Earth, Mars): Small, dense, and rocky; formed from metals and silicates in the hot inner solar system.
• Outer planets (Jupiter, Saturn, Uranus, Neptune): Large and low-density; formed in the colder outer solar system from ices, gases, and rocky debris.
• Gas giants (Jupiter & Saturn) grew massive because their strong gravity let them hold on to hydrogen and helium.

1.6 Earth's Internal Structure

Sketch Earth’s internal structure and label and describe the main subdivisions

Formation of Earth

• As material accumulated forming early Earth, temperature was high enough for iron and nickel to melt.
• Formation of Earth’s layered structure
• Metals sank to the center
• Chemical differentiation:
  • Molten rock rose to produce a primitive crust
  • Established the three basic divisions of Earth’s interior: core, mantle, and crust
• A primitive atmosphere evolved from volcanic gases

Layers Based on Physical Properties

• Lithosphere
• Asthenosphere
• Transition Zone
  • (Increase in density)
• Lower Mantle
• Outer Core
• Inner Core

Chemical Composition

• Crust:
  • Oceanic Crust (7 km thick) composed of basalt
  • Continental Crust (35-70 km thick) composed of granodiorite
• Mantle:
  • Approx. 2,900 km thick and composed of peridotite
• Core:
  • Composed of iron-nickel alloy

1.7 Rocks and the Rock Cycle

Sketch, label, and explain the rock cycle

What are rocks?

• Rocks: Solid aggregates of minerals (or mineral-like matter), most common material making up Earth.
• Igneous rocks: Form from cooling and solidification of molten rock (magma/lava).
• Sedimentary rocks: Form from weathered particles of preexisting rocks that are deposited, compacted, and lithified into layers near the Earth’s surface
• Metamorphic rocks: Form when preexisting rocks are altered by heat, pressure, or chemically active fluids.

The Rock Cycle:

• Allows us to visualize the interrelationships among different parts of the Earth system.
• Helps us understand the origin of igneous, sedimentary, and metamorphic rocks.
• Identify the relationship between each rock type and how they are linked via Earth processes.

1.8 The Face of Earth

List and describe the major features of the ocean basins and continents

• Earth’s surface is divided into ocean basins and continents.
  • Their elevation difference is a result of differences in their relative density and thickness.
• Ocean basins
  • Average depth is 3.8 km below sea level
  • Composed of approximately 7 km thick basaltic rocks
• Continents
  • Relatively flat plateaus average 0.8 km above sea level
  • Composed of granitic rocks, average 35 km thick

• Drops several kilometers
• Can be very steep disturbments

• Several kilometers underwater
• Giant mountains deep underwater
• Trenches - some of the deepest places
  • Mariana's Trench

Continents

Continents consist of mountain belts, cratons, shields, and stable platforms.

• Mountain belts are the most prominent features of continents.
  • Stable interiors of continents, called cratons
• Shields are expansive, flat regions of deformed crystalline rocks within cratons.
• Stable platforms are the flat portions of cratons covered with a thin veneer of sedimentary rocks.

End of Ch. 1 - Concept Checks

1.1 Geology: The Science of Earth

1. Name and distinguish between the two broad subdivisions of geology.
2. List at least three different geologic hazards.
3. Aside from geologic hazards, describe another important connection between people and geology.

1.2 The Development of Geology

1. Describe Aristotle’s influence on geology.
2. Contrast catastrophism and uniformitarianism. How did each view the age of Earth?
3. How old is Earth?
4. Using the Geological Time Scale, list the eon, era, period, and epoch in which we live.

1.3 The Nature of Scientific Inquiry

1. How is a scientific hypothesis different from a scientific theory?
2. Summarize the basic steps followed in many scientific investigations.

1.4 Earth as a System

1. List and briefly contrast the four spheres of the Earth system.
2. How much of Earth’s surface do oceans cover? What percentage of Earth’s water supply do oceans represent?
3. What is a system? List three examples.
4. What are the two sources of energy for the Earth system?

1.5 Origin and Early Evolution of Earth

1. Name and briefly outline the theory that describes the formation of our solar system and then describe the steps in the formation of Earth’s layered structure.
2. List the inner planets and outer planets. Describe basic differences in size and composition.
3. Explain why density and buoyancy were important in the development of Earth’s layered structure

1.6 Earth's Internal Structure

1. Name and describe the three major layers defined by their chemical composition.
2. Contrast the characteristics of the lithosphere and the asthenosphere.
3. Why is the inner core solid?

1.7 Rocks and the Rock Cycle

1. List two rock characteristics that are used to determine the processes that created a rock.
2. Sketch and label a basic rock cycle. Make sure to include alternate paths.

1.8 The Face of Earth

1. Contrast ocean basins and continents.
2. Name the three major regions of the ocean floor. What are some features associated with each?
3. Describe the general distribution of Earth’s youngest mountains.
4. What is the difference between shields and stable platforms?