Understanding Earth

Understanding Earth: An Understanding Earth: An Introduction to Physical GeologyIntroduction to Physical Geology

Understanding Earth: An Understanding Earth: An Introduction to Physical GeologyIntroduction to Physical Geology

Chapter 1Chapter 1Chapter 1Chapter 1

Outline• Introduction to Earth Systems

• What is Geology?

• How Does Geology Relate to the Human Experience?

• How Does Geology Affect Our Everyday Lives?

• Global Geologic and Environmental Issues Facing Humankind

• The Origin of the Solar System and the Differentiation of Early Earth

• Why is Earth a Dynamic Planet?

• Geology and the Formulation of Theories

• Plate Tectonic Theory

• The Rock Cycle

• Geologic Time and Uniformitarianism

• How Does the Study of Geology Benefit Us?

Outline (cont’d)

ObjectivesUpon completion of this chapter you will have

learned that:

• Geology is the study of Earth.

• Earth is a complex integrated system.

• Geology plays an important role in the human experience.

• The solar system evolved from a turbulent rotating cloud of matter surrounding the embryonic Sun.

• Theories are based on scientific method.

• Plate tectonic theory revolutionized geology.

• The rock cycle illustrates the interrelationships between Earth’s internal and external processes and shows how and why the three major rock groups are related to each other.

• An appreciation of geologic time and uniformitarianism is central to understanding the evolution of Earth and its biota.

• Geology is an integral part of our lives.

Objectives (cont’d)

Introduction to Earth Systems

• A system is a combination of related parts that interact in organized fashion. Changes in components of the system can affect the entire system as well as any connected systems.

Introduction to Earth Systems• Earth, a complex, dynamic system, consists of atmosphere, biosphere, lithosphere, hydrosphere, mantle, and core subsystems. Energy and matter are exchanged and recycled among these sub- systems.

• The Aral Sea disaster is a human-induced example of how changes in a minor component of one system can cause changes in other systems. Here changes in a small component of the hydrosphere produced adverse affects in components of the atmosphere and biosphere systems.

Introduction to Earth Systems: The Aral Sea

• Reduced to 1/2 its original area and 1/3 its original volume. Diversion of water for cotton irrigation altered the balance between river input and evaporation.

• Increased salinity killed all native fish and cost thousands of jobs. Salt and dust blown from the dry lake damaged the cotton crop and native vegetation, and caused increased respiratory and eye disease and throat cancer.

• Desertification has caused a weather change to colder winters and hotter, drier summers.

Introduction to Earth Systems: The Aral Sea

What is Geology?• Geology is the study of Earth and has traditionally been divided

into two broad areas of interest:

1) physical geology which concerns rocks and minerals and the processes as well as internal and external Earth-processes, and

2) historical geology which examines the origin and evolution of Earth’s continents, oceans, atmosphere, and life.

• Geology is a very broad and diverse discipline with many different specialties that draw on knowledge from related sciences such as astronomy, biology, physics, and chemistry.

• The arts, music, literature, and even the comics contain numerous references to geology.

How Does Geology Relate to the Human Experience?

• The struggle for control of natural resources such as oil, gas, gold, diamonds, etc., is a recurring theme in human history. Throughout history empires have risen and fallen on the distribution and exploitation of natural resources.

• Natural features shaped by geologic processes serve as political boundaries and have shaped the tactics of military campaigns

• Nearly every aspect of geology has some economic or environmental relevance. From these we can trace many connections between geology and various aspects of our lives.

– The uneven distribution of energy and mineral resources and dependence on them shapes international politics and economics.

– Fulfilling our diverse roles as decision makers (members of community planning boards, property owners with mineral rights, homeowners concerned with stream flooding, and parents concerned about the safety of water supply to legislators enacting environmental regulations) requires a basic understanding of geologic processes.

How Does Geology Affect Our Everyday Lives?

• Geologic hazards (earthquakes, volcanic eruptions, landslides) affect many lives. More geologic knowledge is required to lessen the severity of their impact.

How Does Geology Affect Our Everyday Lives?

• The standard of living is dependent on the use of geologic materials, requiring

consumer awareness of how overuse of geologic resources adversely affects the balance of nature, our culture, and

environment. • To insure a future with sufficient natural resources to maintain the standard of living for a larger population, we must achieve sustainable development.

Global Geologic and Environmental Issues Facing Humankind

• The greatest environmental problem facing the world is overpopulation-- Nonindustrialized countries -- food shortage-- Industrialized countries -- rapid depletion of

nonrenewable and renewable resources; pollutants are produced and released into the environment at rates

exceeding the natural recycling rate.

Global Geologic & Environmental Issues Facing Humankind

• Global warming via the greenhouse effect is another important environmental issue. Increased CO2 in the

atmosphere appears to correlate to warmer global temperatures.

• Factors contributing to increased atmospheric CO2 are industrial and automobile emissions and destruction of rain forests.

Origin of the Solar System and Differentiation of the Early Earth

a) cloud of interstellar debris left over from Big Bang condenses via gravitational collapse b) begins to flatten and rotate and matter concentrates at center of cloud (solar nebula) to form embryonic Sun

c) turbulence in solar nebula forms eddies that concentrate matter to form planetesimals

d) embryonic Sun condenses, heats to several million degrees, and resulting

solar radiation blows debris from solar system

e) Sun is born and begins to burn hydrogen; planetary accretion continues to

completiona

c

d

e

b

a) early Earth (4.6 b.y.) had uniform composition and density

b) heat generated by gravitational contraction, collisions with debris in its orbital path and decay of radioactive elements results in (partial) melting; during molten phase dense elements sink to collect in core and lighter silicate minerals flow upward to form mantle and crust

c) differentiation results in layered planet, and emission of gases supplies material for early atmosphere and oceans

Origin of the Solar System and Differentiation of the Early Earth

Why is Earth a Dynamic Planet?• Earth has continuously changed during its 4.6 billion year existence. Examples

include:

1) changes in size, shape, and location of continents and

ocean basins

2) changes in composition of the atmosphere

3) changes in life-forms from past to present

4) formation and destruction of mountains and landscapes.• Volcanoes and earthquakes are evidence of active interior• Folded and fractured rocks record the power of Earth’s internal forces• Earth’s dynamic nature, illustrated by the specific changes and features listed

above, results from interaction among the many subsystems and cycles of the complex Earth system

Geology and the Formulation of Theories• theory (everyday usage) -- a speculative or conjectural explanation; an

unsubstantiated wild guess

• theory (scientific usage)-- coherent explanation supported by a large body of objective evidence; validity of explanation testable by experiment and/or assessment of predictive ability; for example, the law of universal gravitation

• scientific method -- orderly, logical collection and analysis of data about a specified problem; includes testing of tentative explanations, hypotheses; if repeated testing confirms hypotheses, then can propose as a theory, otherwise explanation is rejected and new hypotheses tested; theories subject to refinement by further testing and new data

Plate Tectonic Theory• Milestone in geologic thought equivalent in significance to theory of

evolution in biology

• Framework for understanding Earth processes and features on a global scale

• Helps understand processes by which Earth’s subsystems interact as well as features and phenomena produced by these interactions

• Led to realization that continents and ocean basins (components of the lithosphere), atmosphere, and hydrosphere evolved in concert with mantle and core subsystems of Earth’s interior

Plate Tectonic Theory• The lithosphere is divided into a series of plates that fit like

jigsaw puzzle pieces across the Earth’s surface.

Plate Tectonic Theory• Plates float on the asthenosphere, a partially molten part of the mantle, as they move across Earth’s surface and interact along their boundaries.

• Zones of volcanic and/or earthquake activity mark most plate boundaries.

• Plate movements are responsible for:

1) formation of major landscape features,

2) formation and distribution of geologic resources, and

3) influencing the distribution and evolution of the biosphere.

• There general types of plate boundaries are recognized: convergent, divergent, and transform.

Plate Tectonic Theory

The Rock Cycle - Igneous Rocks• Geologists recognize three major rock groups, each of which

has a characteristic mode of formation. Each major rock group can be subdivided based on composition and texture.

• Igneous rocks form by cooling and crystallization of molten material.

granite

basalt

Faster cooling at Earth’s surface yields extrusive igneous rocks such as basalt.

Slow cooling within Earth produces intrusive igneous rock such as granite.

• Sedimentary rocks form by:

1) consolidation of rock

fragments,

2) precipitation of minerals

from solution

3) compaction of plant or

animal remains

• Sedimentary rocks are very useful for interpreting Earth history

The Rock Cycle - Sedimentary Rocks

limestone

conglomerate

• Metamorphic rocks form beneath Earth’s surface when other rocks are transformed by heat, pressure, and/or chemically active fluids.

• Foliated metamorphic rocks, gneiss for example, contain layers or bands formed by the parallel alignment of minerals due to pressure.

• Nonfoliated metamorphic rocks, such as quartzite, lack pressure-induced layering and commonly form due to heat.

The Rock Cycle - Metamorphic Rocks

gneiss

quartzite

The Rock Cycle - Interrelationships• The rock cycle illustrates the relationships between Earth’s internal and

external processes and relates the formation of the major rock groups to external (weathering, transportation, deposition) and internal processes (melting, metamorphism).

The Rock Cycle - A Plate Tectonic Perspective• Plate movement drives the rock cycle and is responsible for the recycling of

rocks from one major group to another. • For example, heat and pressure generated along convergent boundaries

may lead to melting of and metamorphism of rocks in the descending ocean plate and thereby lead to formation of new igneous and metamorphic rocks.

Geologic Time & Uniformitarianism

• An appreciation for the immensity of geologic time is central to understanding the evolution of Earth and life on Earth.

• The vastness of geologic time sets geology apart from all other sciences except astronomy.

• The geologic time scale was assembled in the 19th century by geologists who arranged information from a multitude of rock outcrops into a sequential chronology based on changes in Earth’s biota through time.

• Development of radiometric dating in the 20th century permitted assignment of absolute age dates to subdivisions of the time scale.

• Uniformitarianism is a cornerstone in the interpretation of Earth’s geologic history. It holds that present-day processes have operated throughout geologic time.

Understanding present-day geologic processes and the features they form is the key to interpreting features preserved in rocks and Earth’s geologic history.

• For example, bird tracks preserved in this 50 million-year-old sedimentary rock were formed the same way bird tracks are formed in soft mud today.

Geologic Time & Uniformitarianism

Geologic Time & Uniformitarianism• Unformitarianism leads us to interpret the features in the

rock to the right as ancient mud cracks formed by desiccation of sediment just as is shown in thepresent-day setting below.