1. An Introduction to Geology

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1.1 Geology The Science of Earth

Geology: The Science of Earth

Geology - The science that examines Earth, its form and composition, and the changes that it has undergone and is undergoing.

Physical and Historical Geology

Physical Geology - Examines the materials composing Earth and seeks to understand the many processes that operate beneath and upon its surface.

Historical Geology - Aim is to understand the origin of Earth and its development through time. Strives to establish an orderly chronological record of physical and biological changes.

The study of physical geology logically precedes the study of Earth history because we must first understand how Earth works before we attempt to unravel its past.

Geology is a science that seeks to expand our knowledge of the natural world and our place in it.

Geology, People, and the Environment

Natural hazards affect millions of people worldwide and are responsible for staggering damages.

Hazardous Earth process that geologists study are volcanoes, floods, tsunamis, earthquakes, and landslides.

More people live in cities than rural areas. This urbanization concentrates millions of people into megacities vulnerable to natural hazards.

Development destroys natural defenses such as wetlands and sand dunes. Poor construction practices and rapid population growth are increasing vulnerability.

Climate change is linked to sea-level rise.

Concept Checks

Name and distinguish between the two broad subdivisions of geology.

List at least three different geologic hazards.

Aside from geologic hazards, describe another connection between people and geology.

1.1 Flashcards

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1.2 The Development of Geology

The Development of Geology

Greek philosopher Aristotle's explanations about the natural world were arbitrary pronouncements.

Aristotle's explanations unfortunately continued to be viewed as authoritative for many centuries, thus inhibiting the acceptance of more up-to-date ideas.

Catastrophism

In the mid-1600s James Ussher constructed a chronology of human and Earth history in which he calculated the Earth was only a few thousand years old. (4004 B.C.)

Thought about Earth's features and processes was influenced by a guiding doctrine called catastrophism.

The Birth of Modern Geology

Scottish physician James Hutton put forth a fundamental principle that is a pillar of geology today: uniformitarianism.

The Magnitude of Geologic Time

Our understanding of radioactivity allows us to accurately determine numerical dates for rocks that represent important events in Earth's distant past.

The age of Earth is about 4.6 billion years.

100 million years ago may be characterized as "recent" by a geologist.

10 million years may be called "young."

Concept Checks

Describe Aristotle's influence on geology.

Contrast catastrophism and uniformitarianism. How did each view the age of Earth?

How old is Earth?

Why is an understanding of the magnitude of geologic time important for a geologist?

1.2 Flashcards

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1.3 The Nature of Scientific Inquiry

The Nature of Scientific Inquiry

The natural world behaves in a consistent and predictable manner that is comprehensible through careful, systematic study.

The goal of science is to discover patterns in nature and use this knowledge to predict what should or should not be expected.

Scientists collect scientific facts through observation and measurement.

Hypothesis

Once facts have been gathered and principles have been formulated, investigators construct a scientific hypothesis.

Extensive research is conducted and the results are made available in scientific journals.

The verification process requires predictions be made and tested through comparison against objective observations of nature.

Hypotheses that fail rigorous testing are discarded.

Theory

When a hypothesis has survived scrutiny and competing hypotheses have been eliminated, a hypothesis may be elevated to a scientific theory.

Scientific Methods

The process, in which researchers gather facts through observations and formulate scientific hypotheses and theories, Is called the scientific method.

A question is raised about the natural world.

Scientific data that relate to the question are collected.

Questions that relate to the data are posed, and one or more working hypotheses are developed that may answer these questions.

Observations and experiments are developed to test the hypothesis.

The hypotheses are accepted, modified, or rejected. based on extensive testing.

Data and results are shared with the scientific community for critical examination and further testing.

Plate Tectonics and Scientific Inquiry

In the early part of the twentieth century continental drift was proposed: the idea that the continents moved about the face of the planet.

More than 50 years later the theory that finally emerged was called the theory of plate tectonics.

Concept Checks

How is a scientific hypothesis different from a scientific theory?

Summarize the basic steps followed in many scientific investigations.

What explains the fact that continental drift is considered a hypothesis but plate tectonics is considered a theory?

1.3 Flashcards

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1.4 Earth's Spheres

Hydrosphere

The hydrosphere is a dynamic mass of water that is continually on the move, evaporating from the oceans to the atmosphere, precipitating to the land, and running back to the ocean again.

The global ocean blankets nearly 71 percent of the Earth's surface to an average depth of about 3800 meters (12,500 feet. Accounts for about 97% of the Earth's water.

The hydrosphere also includes the freshwater found underground and in streams, lakes, and glaciers.

Atmosphere

Earth is surrounded by a life-giving gaseous envelope called the atmosphere.

It provides the air that we breathe but also protects us from the Sun's intense heat and dangerous ultraviolet radiation.

Produces effects we call weather and climate.

Biosphere

The biosphere includes all life on Earth.

Geosphere

Lying beneath the atmosphere and the oceans is the solid Earth, or geosphere.

The geosphere extends from the surface to the center of the planet, a depth of nearly 6400 kilometers (4000 miles).

Soil, the thin veneer of material at Earth's surface that supports the growth of plants, may be thought of as part of all four spheres. The solid portion is a mixture of weathered rock debris (geosphere) and organic matter from decayed plant and animal life (biosphere). The decomposed and disintegrated rock debris is the product of weathering processes that require air (atmosphere) and water (hydrosphere). Air and water also occupy the open spaces between the solid particles.

1.4 Concept Checks

List and describe Earth's four spheres.

Compare the height of the atmosphere to the thickness of the geosphere.

How much of Earth's surface do oceans cover? What percentage of Earth's total water supply do oceans represent?

To which sphere does soil belong?

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1.5 Earth as a System

Earth System Science

The hydrosphere, atmosphere, biosphere, and geosphere and all of their components can be studied in a complex and continuously interacting whole that we call the Earth system.

System - a group of interacting, or interdependent, parts that form a complex whole.

The Earth System

The Earth system is powered by energy from two sources.

The sun drives energy into weather and climate, ocean circulation, and erosional processes.

Heat remaining from our planet formed and heat that is continuously generated by radioactive decay power the internal processes that produce volcanoes, earthquakes, and mountains.

1.5 Concept Checks

What is a system? List three examples.

What are the two sources of energy for the Earth system?

Predict how a change in the hydrologic cycle, such as increased rainfall in an area, might influence the biosphere and geosphere in that area.

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1.6 Early Evolution of Earth

Origin of Planet Earth

The universe begins about 13.7 billion years ago with the Big Bang, an incomprehensibly large explosion that sent all matter of the universe flying outward at incredible speeds.

Nebula Theory - Proposes that the bodies of our solar system evolved from an enormous rotating cloud called the solar nebula.

Formation of Earth's Layered Structure

Chemical differentiation established the three basic divisions of Earth's interior - the iron-rich core; the thin primitive crust; and Earth's largest layer, called the mantle.

Large quantities of gaseous materials escaped from Earth's interior gradually evolving a primitive atmosphere.

Continents and ocean basins evolved gradually over the past 4 billion years (continental crust).

Concept Checks

Name and briefly outline the theory that describes the formation of our solar system.

List the inner planets and outer planets. Describe the basic difference in size and composition.

Explain why density and buoyancy were important in the development of Earth's layered structure.

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1.7 Earth's Internal Structure

Earth's Crust

Crust - Earth's relatively thin, rocky outer skin (continental crust and oceanic crust).

The oceanic crust is roughly 7 kilometers (5 miles) thick and composed of the dark igneous rock basalt.

The continental crust averages about 35 kilometers (22 miles) thick but may exceed 70 kilometers (40 miles) in some mountainous regions.

The upper crust has an average composition of a granitic rock called granodiorite.

Continental rocks have an average density of about 2.7 g/cm^3 and some have been found to be more than 4 billion years old.

Oceanic crust is younger (180 million years or less) and denser (about 3.0 g/cm^3).

Mantle

Mantle - A solid, rocky shell that extends to a depth of about 2900 kilometers (1800 miles) and takes up more than 82 percent of Earth's volume.

The upper mantle extends from the crust-mantle boundary down to a depth of about 660 kilometers (410 miles).

Lithosphere - Top portion of the upper mantle and is the stronger part. Consists of the entire crust plus the uppermost mantle and forms Earth's relatively cool, rigid outer shell. Averaging 100 kilometers in thickness, but 250 kilometers thick below the oldest parts of the continents.

Asthenosphere - Weak layer with a small amount of melting to a depth of 410 kilometers.

The lithosphere is able to move independently of the asthenosphere.

Transition Zone - From about 410 kilometers to about 660 kilometers in depth. Identified by a sudden increase in density from about 3.5 to 3.7 g/cm^3 because minerals in the rock peridotite respond to the increase in pressure by forming new minerals with closely packed atomic structures.

Lower Mantle - From a depth of 660 kilometers to the top of the core, at a depth of 2900 kilometers (1800 miles). The rocks within the lower mantle are very hot and capable of extremely gradual flow.

Earth's Core

Core - Thought to be composed of an iron-nickel alloy with minor amounts of oxygen, silicon, and sulfer with an average density of nearly 11 g/cm^3 and approuaches 14 times the density of water at Earth's center.

Outer Core - A liquid layer 2270 kilometers (1410 miles) thick. It is the movement of metallic iron within this zone that generates Earth's magnetic field.

Inner Core - a sphere with a radius of 1216 kilometers (754 miles). Despite higher temperatures, the iron in the inner core is solid due to the immense pressures.

Concept Checks

List and describe the three major layers defined by their chemical composition.

Contrast the lithosphere and asthenosphere.

Distinguish between the outer core and the inner core.