Geology is science that studies Earth + other solar system bodies –their origin, their

evolution, etc

• Involves enormous periods of time

• Involves scientific method

based on experimentation + principle that every physical event has physical explanation

tentative explanation based on data

• if hyp has lg amt of support, is elevated to

representation of some

aspect of nature based on set of

hypotheses; can test by comparing

predictions with observations

“code of ethics”

1) Must acknowledge contributions of others

2) Must not fabricate / falsify data

3) Must be responsible in training next generation

• Unmoving spherical Earth

• Earth-centered

(geocentric) universe

• Planets moved on nested

crystalline spheres w/ no

gaps between them

1) elliptical orbits

2) sweep out equal areas

in equal times

3) square of period = cube

of semimajor axis

• The Earth is very roughly spherical

• The Earth orbits the Sun

• The other planets also orbit the Sun

• The Sun is a star

• The Sun is one of several billions of

stars in the Milky Way galaxy

• The Milky Way galaxy is one of

billions of galaxies

• The universe itself is expanding

James Hutton

his historical concept of geology

first advanced in late 1700’s 

(“no vestige of a beginning - no

prospect of an end”);

discovered deep time

Principle of

uniformitarianism

“present is

key to the past”; theories of

catastrophism not necessary

“Big Bang”

theory

most accepted scientific

description of origin of universe

Cosmic explosion

13 billion years ago;

universe has expanded

+ thinned

Formation of solar system

~4.5 billion

years ago (this is

timeframe of the

geologist)

“nebular hypothesis”

a tentative explanation:

contraction of rotating cloud under force of

gravity

Our solar system: planet composition

varied w/ distance from Sun

• Inner planets: small; rx + metals; volatile

materials not retained in quantity

• Giant outer planets: volatiles swept

pushed to cold outer solar system to form

giant planets (ices + gases surrounding

rocky cores)

Differentiation

• energy:

1) impacts + 2) radioactive energy

(e.g., U, K)

• early large impact may have produced

Moon + changed Earth’s inclination early

in solar system history

The Core

• deepest hole dug by humans = ~11 km

• gravity, seismic, + geochemical data strongly suggest most made up of iron (dense + heavy)

• core molten on outside, but inner core solid where

pressures highest(5200 – 6400 km)

The Mantle

• is material left in middle zone

• is bulk of solid earth

• seismic + geochemical data strongly suggest that has intermediate density, + is formed mostly compounds of oxygen w/ Mg, Fe, Si

The Crust

• materials that floated toward surface of

magma ocean formed Earth’s solid crust

• thin outer layer up to ~40+ km thick

• contains relatively light materials w/ low

melting T’s

• most easily melted compounds of Si, Al,

Fe, Ca, Mg, Na, K

2 heat engines

internal (from initial formation of Earth + from radioactivity)

external (solar energy)

internal energy

drives volcanism + other interior processes

external heat

energizes atmosphere + oceans 

responsible for climate + weather

Earth’s Surface

• not clear what caused initial formation of continents

• repeated melting + solidification of initial

cooled surface ???

allowed lighter elements to become separated

from heavier ones + float to top ???

• origin traceable to water + gases that boiled off during initial heating / differentiation of Earth(water, H, N,C initially bound in minerals, then

freed by partial melting, carried to surface by magmas, + released through volc activity)

• comets may have also contributed

water + carbon dioxide + other gases

• Today, atm mainly made up of N + O, but O only persisted in atm of Earth after photosynthetic algae developed + began releasing O as waste product (slow accumulation of O in atm)

Earth is Composed of a System of

Interacting Components

• 1) Heat from interior drives mantle convection

• 2) Solar energy drives most of biosphere

Mercury

trace atmosphere; no wind or water

very dry; 475oC at surface; dense CO2 atm w/ sulfuric acid droplets; radar: volcanoes,plains, mountains

coalesced as molten body after impact

ejected matter from Earth; no atm., very dry, very ancient surface

cold, thin CO2 atmosphere; polar caps; networks of valleys + channels suggest that it was relatively wet in its early history; 2 moons

Heavy Bombardment Period

• evidence at, e.g., Moon, Mars, + Mercury

• ancient surfaces preserve impact record

• period may have lasted ~600 m.y.

• evidence on Earth destroyed by later geological processes

• impact processes still taking place, but with lower frequency

Plate Tectonics

• unifying theory for geological science;

important re: volcanoes, eq belts, mtn systems, ocean basins

• main idea: Earth’s surface largely affected by formation,movement, interactions, + destruction of large rigid plates at surface of planet

lithosphere (crust + upper mantle):

• strong, solid, outermost shell; 100-200+ km thick; cool + brittle; ~dozen plates

• lithosphere forms from rising hot mantle

  where plates separate, cools as moves

  away from boundary, + sinks back into

  asthenosphere at convergent plate

  boundaries, dragging plate with it

asthenosphere

• solid but weak layer upon which lithosphere rides; weak since almost at melting pt; 100-200 km thick; can “flow”
•  mantle beneath asthenosphere is mostly solid, but is hot + ductile – can flow or “creep” via convection

Earth Through Geologic Time

• Earth ~4.5 B.Y. old

• Oldest preserved rocks on Earth: ~4 B.Y.

• Oldest evidence for water erosion: ~3.8 B.Y.

• Continental masses by ~2.5 B.Y.

• Oldest known fossils of early life (bacteria): ~3.5 B.Y.

Development of Life

• Earth’s atm / hydrosphere believed to have existed just over 4 B.Y. ago

• early atm: water vapor, carbon dioxide, sulfur

dioxide (penetrable by UV rays); perhaps H, N

• earliest known fossils: ~3.5 B.Y.

• based on indirect chemical evidence, life may have first developed ~4 B.Y. ago

theory of plate tectonics

• theory describes movement of plates, + nature of forces

Eduard Suess:

• 19th c.: S continents once part of single continent (“Gondwanaland”)

Alfred Wegener

rift valley

• 1952: rift valley discovered in Mid-Atlantic Ridge by Tharp + Heezen

Ring of Fire

• “Ring of Fire” supported idea of lithosphere

recycling, allowing seafloor spreading without increasing size of Earth

J. Tuzo Wilson

• 1965: J. Tuzo Wilson described global tectonics re: rigid “plates”; 3 basic types of boundaries where plates move apart, come together, or slide past each other

• by 1970, support for plate tectonics very persuasive

“Mosaic of Plates”

• rigid lithosphere broken into ~12 lg, rigid plates in motion over surface; note: plate extents don’t match continents

Divergent boundaries

• plates move apart + new lithosphere created

• normally at “mid-ocean ridge” (chain of mtns beneath oceans)

• characterized by eq’s + volcanoes

• “seafloor spreading”: creation of new seafloor as basins widen

Convergent boundaries

• plates come together + one usually recycled into mantle

Transform-fault boundaries

Rates and History of Plate Motions

• seafloor = “magnetic tape recorder”

• patterns in strength of magnetic fields noted in

seafloor

• patterns (“magnetic anomalies”) parallel to ocean ridges

magnetic epochs

• major normal or reversed periods (~half million yrs)
•  magnetic events: short-lived (<~200,000 yrs)

  • new seafloor generated magnetized in

  direction of Earth’s field at the time

  • as new seafloor generated, record of

  magnetic reversals is generated

modern measurements

astronomical positioning + global positioning system

“The Grand Reconstruction”

• isochrons: contours that connect rocks of equal age

• seafloor progressively older on both sides of mid-ocean rifts

• more widely spaced isochrons indicate periods of faster seafloor spreading

two primary principles used in reconstructions

1) transform boundaries indicate directions of

relative plate movement

2) seafloor isochrons reveal positions of divergent boundaries in earlier times (isochrons ~parallel / symmetrical with boundary of plate separation at relevant time)

• Note: ~all seafloor created since time of breakup of Pangaea

Breakup of Pangaea

Mantle Convection

• Mantle: hot solid capable of flowing like sticky

fluid (warm wax / cold syrup)

• Lithospheric plates participate in flow of mantle

convection system

• Mantle convection poorly understood

Classic Hot Spots

• 1) Iceland (note: also at a divergent margin)

• 2) Island of Hawaii

• 3) Yellowstone Park (Wyoming / Idaho / Montana)

Mineralogy

• study of comp, structure, appearance, stability, occurrence, + associations of minerals

• Minerals: building blocks of rx

• Mineral: naturally occurring, solid crystalline substance, generally inorganic, with specific chemical composition

inorganic minerals

secreted via organic processes are considered minerals (e.g., calcite in foram shells)

Atomic Structure of Matter

• “Atom”: smallest unit of element that retains physical / chemical properties of that element

• Atoms: units of matter that combine in chem rxns

• Atoms divisible into even smaller units

The Structure of Atoms

• Proton: positive electrical charge (+1)

• Neutron: electrically neutral

• Atoms of same chemical element have same # protons, but # neutrons can vary

Atomic Number and Atomic Mass

• atomic number: # protons in atom (thus, all

atoms of a particular element have same

atomic number)

• atomic mass: sum of masses of protons

and neutrons

• isotopes: atoms w/ same # protons but diff

# neutrons (e.g., Carbon-12, Carbon-13, Carbon-14)

Chemical reactions

Atoms “want” full e shells

a) can acquire full shells by loss or gains of e’s

b) can also acquire full shells by “electron sharing” (e.g., C in diamond)

Periodic Table of the Elements

• Elements can have similar chemical properties

• Periodic table organizes elements in order of

atomic number (# protons)

Chemical Bonds

• Ions / atoms in compounds are held together

by electrical forces of attraction between e’s +

protons; chemical bonds

• Ionic bonds: simplest type; “electrostatic”

• Covalent bonds: usu stronger than ionic bonds; formed by sharing e’s (e.g., C in diamond)

Atomic Structure of Minerals

• minerals are 1) crystals / grains; but also 2) assemblages of atoms in 3d arrays

• minerals form by crystallization: materials from

gas or liquid combine in crystalline arrangement

• flat planar surfaces = “crystal faces”

What Causes Minerals to Form?

• 1) Lowering T of a liquid below freezing pt

can start process of crystallization

• 2) “Precipitation” from a solution (as liquids

evaporate)

• 3) Rearrangement of atoms in solids at high T’s and/or P’s (e.g., mica)

Ion Sizes

• ion sizes vary; related to # of e’s + # of electron

shells, + ion’s charge

• most cations relatively small (e’s held tightly)

• most anions relatively lg (e’s held less tightly)

• cations usu fit in spaces betw anions, which

occupy most space of crystal

Cation Substitution

Polymorphs

• diff structure, same chemical composition

• e.g., diamond + graphite; both are C

• e.g., qz + cristobalite – both are SiO2

• defining anion = carbonate ion: CO3 2-

ions separated by layers of Ca cations

• aragonite (also CaCO3)

Oxides

• O bonded to atoms or cations of other

elements, usu metallic ions such as

• most oxide minerals ionically bonded

• oxides include ores of most metals (e.g.,

hematite: Fe2O3)

• compounds of sulfide ion: S2-

• valuable ores include pentlandite, galena,

sphalerite

• most common: pyrite (FeS2)

Sulfates

bonded to calcium + sulfate ions)

• anhydrite: CaSO4 (higher T’s + P’s)

Halides

• group of minerals which contain halogens;

in particular: chlorine (Cl) + fluorine (F)

• halite (NaCl)

• sylvite (KCl)

• fluorite (CaF2)

Silicates

• silicate tetrahedron: 4-sided pyramidal form

• must balance negative charges with positive

Mg2+, Fe2+, or sharing O with other tetrahedra, forming rings, single chains, etc)

Isolated Tetrahedra (Nesosilicates)

• Isolated tetrahedra; each O of tetrahedron

bonded to a cation; cations in turn bonded to O of other tetrahedra

Paired Tetrahedra (Sorosilicates)

• two tetrahedra linked by one oxygen; most are rare, except epidote

Single-Chain Linkages (Inosilicates)

• single open-ended chains

• each chain linked to other chains by cations

Double-Chain Linkages (Inosilicates)

• double chains linked by shared oxygen atoms

• adjacent double-chains can be linked by cations

Tetrahedra Rings (Cyclosilicates)

• chains of tetrahedra form rings; small but important silicate subclass

Sheet Linkages (Phyllosilicates)

• sheets: each tetrahedron shares 3 O with adjacent tetrahedra

• cations may be interlayered with sheets

Frameworks (Tectosilicates)

• 3-d frameworks; each tetrahedron shares all O with other tetrahedra

Physical Properties of Minerals

• “Mohs scale of hardness”

• hardness depends on bond types, + sizes,

charges, packing of atoms

• if bond strength high: cleavage poor

• if bond strength low: cleavage good

• (ionic bonds: excellent cleavage; covalent

bonds: poor or no cleavage)

• cleavage classified by:

1) # planes + pattern

2) quality of surfaces, ease of cleaving

• all minerals show fracture

• conchoidal, fibrous / splintery, etc

• ionically bonded crystals tend to be glassy (vitreous)

• covalently bonded materials more variable (e.g., adamantine)

• pure metals + sulfides tend to show metallic luster (e.g., galena, pyrite)

• pearly luster results from multiple reflections from planes beneath surfaces of translucent minerals (e.g., inner surfaces of clam shells)

• colors depend on presence of certain ions

(e.g., Fe or Cr)

• colors can be distinctive, but color not most reliable clue to a mineral’s identity

Rocks

• rock: naturally occurring solid aggregate

of minerals

• grains can be coarse (lg enough to be seen by naked eye) or fine

“broken”); physically deposited

particles; deposited by running water,

wind, + ice; form layers of sand, silt, +

gravel

• B) Chemical + biochemical sediments; new

substances formed by precipitation from

dissolved materials (e.g., halite, calcium carbonate)

Metamorphic Rocks

lithification

• seds converted to solid rock through process of lithification

• lithification takes place after burial under other layers of sediment

• lithification by:

– 1) compaction (grains squeezed together by

weight of overlying materials);

– 2) cementation (minerals precipitate around

deposited particles + bind them together)

• sand particles -> sandstone; shells + other CaCO3 -> limestone

The Rock Cycle

• intrusive igneous rx: forced their way into

surrounding rock (into “country rock”)

• extrusive igneous rx: formed by eruption of lava + other materials from volcanoes

• 2 major categories of extrusive ig.rx.:

1) lavas;

2) pyroclastic rx (broken pieces of lava thrown high in air)

• pyroclasts : 1) volcanic ash (lithified to “tuff”); 2) pumice; 3) obsidian

• modern classifications based on minerals:

• b) mafic minerals (magnesium + ferrum: “iron”): high in Mg or Fe; crystallize at higher T’s