Intro to Physical GeologyIntro to Physical Geology (EAR 110)(EAR 110)

What is Geology?… … the study of Earth the study of Earth

Two Divisions:Two Divisions:1.1. Physical geologyPhysical geology minerals, rocks, Earth processes minerals, rocks, Earth processes2.2. Historical geologyHistorical geology origin & evolution of continents, origin & evolution of continents,

oceans, atmosphere, & lifeoceans, atmosphere, & life

interdisciplinary interdisciplinary (astronomy, biology, physics, & chemistry)

– MineralsMinerals have practical daily uses. have practical daily uses. (toothpaste, vitamins, drink cans, cosmetics, salt, (toothpaste, vitamins, drink cans, cosmetics, salt, pencil “lead”, jewelry, currency, ceramics, paints, pencil “lead”, jewelry, currency, ceramics, paints, fertilizers, lubricants, abrasives, etc.) fertilizers, lubricants, abrasives, etc.)

Why is Geology Important to You?

– Informed decisions are essential. Informed decisions are essential. (i.e., mineral rights, safety of water supply, (i.e., mineral rights, safety of water supply, stream flooding, community planning boards, stream flooding, community planning boards,

communication to legislators enacting communication to legislators enacting environmental regulations)environmental regulations)

• Knowledge of geologic hazards lessens the Knowledge of geologic hazards lessens the severity of their impact. severity of their impact.

• Standard of livingStandard of living is dependent on the use of is dependent on the use of geologic materials. geologic materials. ((i.e., i.e., Overuse of resources Overuse of resources adversely affects balance of nature, culture, & adversely affects balance of nature, culture, & environmentenvironment..))

Sustainable developmentSustainable development insures future generations sufficient natural insures future generations sufficient natural

resources to maintain standard of living for resources to maintain standard of living for a a larger population.larger population.

A complex, dynamic system

SYSTEMS: atmosphere, biosphere, hydrosphere, lithosphere, mantle, & core.

33 Physical Environments: Physical Environments:1. Solid Earth – core, mantle, & crust2. Hydrosphere – dynamic mass of H2O

The Water CycleThe Water Cycle--evaporation from oceans into the atmosphere

-- precipitation onto land -- water flows back into the oceans

3. Atmosphere – gaseous envelope around Earth 

(interaction b/w surface & atm. WEATHER)

Characteristics of Earth’s Core• composed of Fe (minor Ni & other heavy

elements)

• inner core: solid, Fe-rich sphere• outer core: molten metallic layer

They’re compositionally similar.

Magnetic field provided by circulation of the molten outer core

• 82% of Earth ~2900km thick• located below the crust • behaves like a solid when EQs pass

thru it, but can flow slowly (plastic) Divided into regions:Upper: (Asthenosphere)

crust thru upper mantle (660km into Earth)Lower: (Mesosphere)

from a depth of 660km to the outer core

Characteristics of Earth’s Mantle

LITHOSPHERE rigid, solid

Thickness: Average = 15 km 3 km (~2mi) at ocean ridges 70 km (40 mi) in ancient mtn belts

Oceanic: Continental: Basalt/Gabbro Andesite/Granodiorite more dense (3 g/cm3) less dense (2.7 g/cm3) younger (180 my to pres) older (up to 3.8 by)

Characteristics of Earth’s Crust

Formulation of TheoriesFormulation of Theories• theorytheory speculative explanation; wild guess speculative explanation; wild guess

• theorytheory (scientific) (scientific) coherent explanation supported by large body of evidence; coherent explanation supported by large body of evidence; validity of explanation testable by experiment validity of explanation testable by experiment

How are theories born?How are theories born? The Scientific MethodThe Scientific Method

Refinement occurs by further testing.Refinement occurs by further testing.

The Scientific MethodThe Scientific Method1.1.      Collection of DataCollection of Data

gather scientific facts thru gather scientific facts thru observations & observations & measurements measurements

2.2.      Hypothesis formationHypothesis formation theory vs. hypothesis?theory vs. hypothesis?

3.3.      Tests of the hypothesisTests of the hypothesis develop experiments for testingdevelop experiments for testing

4.4.      Acceptance, modification, or rejection of the Acceptance, modification, or rejection of the hypothesishypothesis

Plate Tectonic Theory

Lithosphere is divided into plates that fit like jigsaw puzzle pieces across Earth’s surface.

Plate Tectonics Theory• Continental drift Continents moved across Earth’s surface. (50 yrs+ for acceptance)

• Plates float on asthenosphere as they move & they interact along their boundaries.

• Plate movement is driven by the unequal distribution of heat w/in Earth.Plate movement is driven by the unequal distribution of heat w/in Earth. 1) major landscape features (mtns, valleys) 2) distributes natl. resources 3) distribution & evolution of the biosphere

Types of Plate Boundaries

CONVERGENT: (subduction zones)**dense plates subduct under less dense plates**subducted plate goes into the mantle & melts

DIVERGENT: (mid-ocean ridges) **seafloor spreading fractures open, molten mat.

from asthenosphere fills fractures

TRANSFORM FAULT: plates move horizontally past one another w/out consuming old lithosphere or generating new lithosphere

The Rock Cycle

……relates the formation of the major relates the formation of the major rock groups to rock groups to internal & external internal & external processesprocesses

Uniformitarianism [late 1700s] 

James Hutton — Scottish physician… very intelligent …not able to convey his thoughts

 

“The present is the key to the past.” **Laws that govern the physical, chemical, and biological processes occurring now on the earth, also operated in the past... (i.e., These processes are unchanging through time.) 

 

Charles LyellPrinciples of Geology (mid 1800s)

 **noted that processes may have been operating at varying rates in the past or that they may not have had the same significance as they do today

Lower Right: Bird tracks

Above: Mudcracks

Geologic Time Scale 19th century geologists arranged info from outcrops based on changes in biota thru time (relative age).

• Radiometric dating (20th century) assigned absolute age dates to the sub-divisions.