EVPP 110 Lecture
Fall 2002, Instructor: Dr. Largen

• Origin of the universe
• unknown for certain
• still being actively researched
• many different theories exist
• Big Bang theory
• inflation theory
• cold dark matter theory
• origin theories are difficult to test

• Age of the universe
• unknown for certain
• still being actively researched
• several different methods exist for calculating age of universe, using
• velocities and distances of galaxy clusters
• information about stars & their life cycles
• age estimates vary greatly by source
• ranging from 8 billion to 14 billion years old

• origin and age of the universe
• most "popular" origin theory
• Big Bang Theory
• most popular age estimate
• ~ 12 billion years old
• diameter of the universe
• thought to have been continually increasing since its creation
• at present, ~ 2 x 10²³ km

• universe is thought to have had a dynamic adolescence
• from ~12 billion years ago (BYA) to ~7 BYA
• galaxies, stars and planets of universe were formed, destroyed, re-formed
• birth of Earth
• ~7 BYA
• a red giant star in vicinity of present Earth catastrophically exploded (supernova)
• ~4.6 BYA
• remnants of that explosion form our solar system, including the Earth

• After collapse of red giant
• a rotating, dense cloud (solar nebula) remained
• as cloud cooled, it condensed and contracted
• rotating faster
• forming a flattened disk, thinnest at edges
• as contraction continued, rings of material separated from the cloud
• which in turn, condensed to form planets

• Resulting 9 planets can be grouped
• terrestrial plants
• Jovian (non-terrestrial) planets
• Pluto

• terrestrial plants
• because they are "earth-like"
• rocky with metallic centers
• heavier materials that stayed nearer sun
• Mercury, Venus, Earth, Mars

• Jovian (non-terrestrial) planets
• because they are similar to Jupiter
• composed mostly of liquids and gases
• lighter materials that boiled away from areas nearest to the sun
• Jupiter, Saturn, Uranus, Neptune
• Pluto
• anamolous; terrestrial but outer

• Why is the Earth so "special" relative to the other planets?
• Temperature
• presence & composition of atmosphere
• water
• continued tectonic activity

• 4.6 billion years old - current estimate
• great age of the Earth has not always been known or agreed upon
• Greek philosophers
• Earth ageless - no beginning or end to time
• Biblical scholar
• Bishop Ussher (1664)
• put age at 5,668 years
• concluded Earth was formed on October 26, 4004 B.C, based on a literal translation of Bible

• Throughout much of human history
• was believed that major physical features of Earth were fixed and unchanging
• continents, oceans, mountains, valleys were all in their "original" locations and would always remain in those locations, unchanged

• Catastrophism
• concept subscribed to by most natural sciences up through early 19th century
• proposes that supernatural forces caused catastrophic events that re-shaped the physical landscape
• Earthquakes
• Volcanic eruptions
• Floods

• With rise of scientific thought and explorations
• evidence against catastrophism grew over the centuries

• Formulated both the Principle of Superposition and Principle of Original Horizontality in 1669

• Layers on bottom were deposited first, and are the oldest (A older than B, B older than C, etc.)
• In any unaltered sequence of rocks, oldest is at bottom, youngest at top

• Almost all strata are initially more nearly horizontal than vertical
• therefore, any strongly sloped stratum had to have been tilted by external forces after it was formed

• Geologic processes happening today operated in a similar fashion in the past, so provide guidance in studying the earth’s history

• Principle of uniformitarianism
• proposed by James Hutton in 1785
• fundamental to modern science of geology
• holds that laws of nature have not changed over time, were same in past as now
• actualism
• when we see ripples on ancient rock composed of hardened sand (sandstone)
• we can assume that they developed in same way that similar ripples develop today
• under influence of certain kinds of water movement or wind

• Principle of uniformitarianism
• James Hutton
• believed that rocks of the past had formed as a result of the same processes that were currently operated at or near surface of the Earth
• such as
• volcanic activity
• accumulation of grains of sand and clay under the influence of gravity

• Relative Age is the answers to a question like, "Which is younger?"
• Relative ages allow us to compare different geologic formations, and determine which is the oldest, next oldest, etc.

• A feature, such as a dike or fault, that cuts formations is younger than the formations it cuts

• fault is younger than the beds it offsets

• Fragments of other rocks contained within the body of a rock are older than the rock

• Rock fragments in this conglomerate are older than the conglomerate itself

Principle of Faunal Succession -
(proposed by William Smith (1769-1839))

• states that over time, organisms on earth have changed in a definite order that is reflected in fossil record
• Rocks with recently evolved life forms are younger than those with older forms

• Organisms with specific characteristics:
• Short lived (geologically)
• Widespread occurrence
• Readily recognized

• Gaps in the rock record
• mark boundaries between rocks of different ages
• may result from non-deposition (a hiatus), or from deposition followed by erosion

• Outcrop photo of volcanic ash layers in Japan
• There is an erosional discontinuity (disconformity) that separates earlier folding in the lower half from folding (above) after later ash flows were deposited.

• Boundary between unlayered igneous or metamorphic rocks, and overlying sequential sedimentary rocks
• Lower rocks show evidence of erosion before the deposition of the sedimentary rocks

• Grand Canyon, Arizona

• seeks to establish age relationships between distant sequences of rock
• often through the use of fossil assemblages, or index fossils
• A key bed, a distinctive stratum that appears at several localities, may also be used

• Determination of the absolute age is usually done using radiometric dating
• Absolute ages are expressed in years, or millions or billions of years, before present

• Requires a parent isotope that undergoes radioactive decays to yield a daughter isotope at a known rate
• Example:
• 14C ® ¹⁴N
• Radioactive decay follows an exponential decay law

• time necessary for half of original atoms of parent isotope to decay into daughter isotope

• In the previous example,
• 14C ® ¹⁴N
• 14C is the parent, and ¹⁴N is the daughter
• The half-life, t_½, is 5730 years

• Eons
• largest divisions of time, beginning with the Archean (4.6 to 3.8 billion years ago)
• Eras (subdivisions of eons)
• defined by dominant life forms
• Periods (divisions of eras)
• based on smaller scale changes
• Epochs (divisions of periods)
• based on detailed, smaller scale changes

• Archean Eon (4.6bya-2.5bya)
• Proterozoic Eon (2.5bya-543mya)
• Phanerozoic Eon (543mya-present) "interval of well-displayed life"
• Paleozoic Era (543mya-251mya) "old life"
• 8 periods; Cambrian, Ordovician, Silurian, Devonian, Mississippian, Pennsylvania, Permian
• Mesozoic Era (251mya-65mya) "middle life"
• 3 periods; Triassic, Jurassic, Cretaceous
• Cenozoic Era (65mya-present) "modern life"
• Paleogene Period (65mya-24mya)
• 3 epochs; Paleocene, Eocene, Oligocene
• Neogene Period (24mya-present)
• 4 epochs; Miocene, Pliocene, Pleistocene, Holocene

Paleozoic Era (543mya-251mya)

• Trilobite fossil, early Paleozoic era

Mesozoic Era (251mya-65mya)

Cenozoic Era (65mya-present)

• "age of mammals"
• Kangaroos are marsupials, a type of mammal
  

• Ecosphere
• entire earth system
• includes all other spheres
• Lithosphere
• solid earth, including earth’s crust & part of upper mantle
• Hydrosphere
• liquid envelope of water which surrounds our planet
• Atmosphere
• layer of gas (air) which surrounds our planet
• Biosphere
• living organisms which inhabit all of above spheres.

• "Layman’s" description
• hot, dense, solid inner iron core
• hot, dense, molten iron outer core
• thick, rocky mantle
• thin, rocky crust
• Two ways typically used to formally describe Earth’s structure
• chemical-based description
• mechanical-based

• chemical-based description
• Crust
• Mantle
• Core

• outermost layer or shell of the Earth
• represents <0.1% of Earth's total volume
• total depth is ~100km
• floats on upper mantle
• is broken into 16 plates

• Nine elements compose ~99% of mass of Earth’s crust
• oxygen = 45%
• silicon = 27%
• aluminum = 8%
• iron = 5.8%
• calcium = 5.1%
• magnesium = 2.8%
• sodium = 2.3%

• can be divided into
• continental
• 30-60km thick
• composed of Al, Ca, K-rich silicate ("granite")
• density ~2.8 g/cm³
• oceanic
• 6-10km thick
• Fe, Mg-rich silicate ("basalt")
• density ~3.0 g/cm³

• zone of Earth below crust & above core
• ~3000km thick
• consists of soft rock, mostly Fe, Mg-rich silicates
• density ~3.2-5.0 g/cm³
• constitutes ~ 67% of Earth’s mass
• can be divided into
• upper mantle
• transition zone
• lower mantle

• central zone Earth's interior
• ~3000km thick
• composed of metallic iron
• no silicate
• density ~10 g/cm³
• can be divided into
• inner core
• transition zone
• outer core

• Mechanical-based description
• Lithosphere
• Asthenosphere
• Mesosphere
• Outer Core
• Inner Core

• solid portion of Earth
• as compared with atmosphere & hydrosphere
• includes crust & part of upper mantle
• ~100 km thick
• rigid
• very strong, rigid
• cool

• layer or shell of Earth below lithosphere
• plastic - but solid
• very weak
• hot
• ~200km thick
• is part of upper mantle

• layer or shell of Earth below asthenosphere
• plastic
• weak, but stronger than asthenosphere
• hot
• ~2600km thick
• is remainder mantle

• Molten
• iron, nickel, dissolved sulfur and oxygen
• constitutes ~30% of Earth’s mass
• ~2200km thick
• convection currents in this region generate Earth’s magnetic field

• solid
• mostly iron, some nickel
• ~1400km thick
• constitutes ~2% of Earth’s mass
• floats in middle of molten outer core
• pressure reaches ~3 million atmospheres
• temperatures range from 4000-5000°C

• is hot and dense
• weight of upper layers presses on interior
• extreme compression leads to extreme heating
• results in extremely hot and compressed deep interior
• since metals are heavy and rocks are light
• heavy metals sink to center (iron and nickel)
• lighter minerals float to surface (silicates)

• temperature
• increases nonlinearly with depth
• pressure
• increases linearly with depth
• density
• increases with depth
• combination of temperature and pressure determines when materials in Earth will be molten versus solid
• also affects production of convection process in asthenosphere

• condition of equilibrium, comparable to floating, of units of lithosphere above asthenosphere
• Crustal loading, as by ice, water, sediments, or volcanic flows, leads to isostatic depression or downwarping
• Crustal unloading, as by erosion, or melting of ice, to isostatic uplift or upwarping

• Based on 6 lines of evidence
• shapes of continents and continental shelfs
• similarities

• 550 MYBP

• Extinct group of seed plants that arose during the Permian on the great southern continent of Gondwana

• The biggest objection was the lack of a mechanism for moving continents
• Wegener spent the rest of his life looking for evidence to support his ideas
• He died in Greenland in 1930, while seeking more evidence

• Heat beaker
• Water expands and rises
• It spreads and cools at the top
• Cool water sinks

• Concept came from oceanographic investigations
• Uses Convection cells, an idea Wegener would have been familiar with

• Why is there so little sediment on ocean floor?
• What are the rock ages so young?

• Continental fossils are at least 3.5 billion years old
• Oldest marine fossils are about 180 million years
• Since life is though to originate in the oceans, why aren’t ocean fossils older?

• Continental lithosphere is about 3.00 grams/cubic centimeter
• Oceanic lithosphere gradually increases in density as it ages, reaching a maximum value of about 3.28 grams/cubic centimeter

• When two plates collide, the denser plate will sink (subside) beneath the less dense plate
• Density differences as small as 1% are enough to cause subduction

• density of the asthenosphere is about 3.3 g/cm³
• Density increases with depth below the surface

• Plates move slowly (up to 15 cm/yr)
• Plates may collide, move apart, or slide past each other
• Friction during plate movement often generates earthquakes

Subduction Zones

• Plots of earthquake foci over time delineate position of subducting plates
• plate which is subducted is always denser than plate which remains on surface

• Plates far from the spreading center will be relatively cold, and therefore dense –
• they will subduct at a steep angle
• Plates near the spreading center will be much warmer
• they will be only slightly denser than surface plate, and the subduction angle will be shallow

• Subducting plate drags part of the surface with it
• Creates large oceanic trenches, which also serve to mark the top of the subduction zones

• Plates subducted under continents create long chains of volcanoes on the continents
• Cascades and Andes are examples
• Plates subducted under oceanic plates create chains of oceanic islands
• Japan, the Philippines, and Indonesia are examples

• movement relative to each other
• Convergent
• plates move toward each other, often a head-on collision
• Divergent
• plates move away from each other
• Transform
• plates move past each other along transform faults

• At any given point, a plate is either oceanic or continental
• Interactions between plates are thus:
• Ocean-ocean (O-O)
• Ocean-continent (O-C)
• Continent-continent (C-C)

• Spreading centers are marked by vents which spew hydrothermal fluids as hot as 350° C
• Fluids contain dissolved metals which precipitate when they hit cold ocean water, encrusting basalt - vents are called "black smokers" for this reason

• Earth has a strong magnetic field
• It is dipolar, with the poles being called north and south

• Present north magnetic pole is located near the south geographic pole
• South magnetic pole is located near the north geographic pole

• Rocks often become magnetized because magnetic mineral grains (usually magnetite) are aligned
• Rock’s magnetic field is fixed at the time magma cools for igneous rocks, or at the time of lithification for sedimentary rocks
• Magnetism of older rocks is called "paleomagnetism"

• In the early 1960’s oceanographic research uncovered a curious phenomenon, called magnetic stripes
• Measurements of the earth’s magnetic field show small variations from place to place

• Magnetic Anomaly = Average regional magnetic field of the earth - magnetic field at a point
• Plotting magnetic anomalies lead to a curious pattern of "stripes", first seen in the Atlantic, later in the Pacific

• Sea-floor spreading
• new magma emerging at a mid-ocean ridge and hardening into rock, which then spread away from the ridge with time
• Polarity reversals
• North and South magnetic poles changing position suddenly

• If we assume sea-floor spreading is occurring, the magnetic field of the rock is fixed, in alignment with the earth’s field, at the time the rock cools
• The measured field above such rocks equals the earth’s field plus the rock’s field (because they are aligned)

• As magma rises, it hardens and its magnetic field matches the present field of the earth - after a polarity reversal, it will be aligned against the earth’s field

• generate magma in the asthenosphere
• below moving lithospheric plates
• may be used as a reference since they are effectively stationary relative to lithospheric plate
• produce volcanoes
• like Hawaiian Islands or many seamounts or guyots (mountains that made it above sea-level, then were flattened by wave erosion)

• A sudden motion or trembling in the Earth caused by the abrupt release of slowly accumulated strain
• Strain is a change in the shape or volume of a body as a result of stress

• initial rupture point of an earthquake
• where strain energy is first converted to elastic wave energy
• point within Earth which is center of an earthquake

• The point on the Earth's surface that is directly above the focus of an earthquake

• An instrument that detects, magnifies, and records vibrations of Earth, especially earthquakes
• resulting record is a seismogram

• Seismogram showing an earthquake - the three different traces represent vibrations in different directions
• First peaks are P waves, the second peaks the S waves

• Numerical scale of earthquake magnitude
• Devised in 1935 by the seismologist C.F. Richter
• Defined local magnitude as the logarithm, to the base 10, of the amplitude in microns of the largest trace deflection that would be observed on a standard torsion seismograph at a distance of 100 km from the epicenter

• Measures vibrational amplitude of earth in response to seismic waves
• Does NOT measure energy release

• Arbitrary scale of earthquake intensity, ranging from I (detectable only instrumentally) to XII (causing almost total destruction)
• Based on human perception of the earthquake, and damage observed after the earthquake is over

• A great earthquake releases the equivalent of 1 billion tons of TNT or more, over a period of 1-2 minutes
• Most intense energy release per unit time of any natural event

• Earthquakes are classified by the depths of their foci below the surface, as follows:
• Shallow 0-70 kilometers
• Intermediate 70-300 kilometers
• Deep 300-700⁺ kilometers

• Earthquakes can cause damage in a number of ways
• Building Collapse
• Tsunami waves
• Seiche waves
• Landslides
• Liquefaction
• Fire
• Disease

• Gravitational sea wave produced by any large-scale, short-duration disturbance of the ocean floor
• Disturbances caused principally by a shallow submarine earthquake, but also by submarine earth movement, subsidence, or volcanic eruption

• Free or standing-wave oscillation of the surface of water in an enclosed or semi-enclosed basin (as a lake, bay, or harbor)

• Earthquakes may trigger mass movement of rock and sediment on unstable slopes
• Damage is most likely to occur after fire removes vegetation, or clear-cutting of forests

• Liquefaction is a physical process that takes place during some earthquakes that may lead to ground failure
• As a consequence of liquefaction, soft, young, water-saturated, well sorted, fine grain sands and silts behave as viscous fluids rather than solids

• Fire often does more damage than the earthquake itself
• Underground pipelines and tanks rupture
• Above ground tanks may rupture or tip over, spilling contents
• Water lines break
• Streets are blocked by debris
• Downed electrical lines may spark, setting off fires

• Earthquakes can cut underground sewer and water lines
• No drinking water
• Only available water is contaminated

• A vent in the surface of the Earth through which magma and associated gases and ash erupt
• Also, the form or structure, usually conical, that is produced by the ejected material
• Plural: volcanoes
• Etymology: the Roman deity of fire, Vulcan

• Magma spews upward with great force through a central vent

• Volcanic eruptions may occur much more quietly along long cracks in the ground

• Large volcanic eruptions can block a great deal of the sun’s energy from reaching the earth’s surface
• This cools the climate until the tephra particles sink to the surface

• Located in the Sunda strait between the islands of Java and Sumatra

• A swiftly flowing, turbulent gaseous cloud, sometimes incandescent, erupted from a volcano and containing ash and other pyroclastics in its lower part; a density current of pyroclastic flow
• Etymology: French, "glowing cloud"

• Man cannot stop subduction, or magma generation - therefore, the prediction of imminent eruption becomes very important