historical geology - ccsf home page · historical geology • the study of the origin and evolution...

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HISTORICAL GEOLOGYHISTORICAL GEOLOGY

Earth is a Dynamic and Earth is a Dynamic and Evolving PlanetEvolving Planet

• Changes in its surface

• Changes in life

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Historical GeologyHistorical Geology

• The study of the origin and evolution of the earth and life.– Placing events in order– Explaining how and why events took place

• Plate Tectonics: Earth’s outermost part is composed of a series of moving plates whose interactions have affected the planets physical and biological history.

• Organic Evolution• Geologic Time

PLATE TECTONICS

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Historical GeologyHistorical Geology

• The study of the origin and evolution of the earth and life.– Placing events in order– Explaining how and why events took place

• Plate Tectonics • Organic Evolution: Earth’s biota has evolved or

changed throughout its history.• Geologic Time

ORGANIC EVOLUTION

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Historical GeologyHistorical Geology

• The study of the origin and evolution of the earth and life.– Placing events in order– Explaining how and why events took place

• Plate Tectonics • Organic Evolution • Geologic Time: The physical and biological changes that

have occurred on Earth have done so over very long periods of time.

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Historical GeologyHistorical Geology

• The study of the origin and evolution of the earth and life.– Placing events in order– Explaining how and why events took place

• Plate Tectonics • Organic Evolution • Geologic Time

– In all cases, principles and theories of Historical Geology are derived from data gathered by Scientific Method

GeologyGeology

• Study of the Earth– Earth as a system and subsystems p.3 fig. 1.1

• Atmosphere• Hydrosphere• Biosphere• Lithosphere (plates)• Mantle• Core

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AtmosphereAtmosphere

HydrosphereHydrosphere

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BiosphereBiosphere

Lithosphere, Mantle, CoreLithosphere, Mantle, Core

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Fig. 1-1, p. 3

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What is Geology ?What is Geology ?

• Physical Geology– Earth materials– Physical processes

• Historical Geology– Earth materials and processes– Origin and evolution of Earth– Origin and evolution of Life

Earth Materials and ProcessesEarth Materials and Processes

• Minerals and Rocks• Processes such as weathering,

sedimentation, lithification, uplift/orogeny, folding and faulting, formation of unconformities

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Historical GeologyHistorical Geology• In historical geology we study

– changes in our dynamic planet– how and why past events happened– implication for today’s global ecosystems

• Principles of historical geology – not only aid in interpreting Earth’s history– but also have practical applications

• William Smith, an English surveyor/engineer– used his study of rock sequences and fossils– to predict the kinds and thicknesses of rocks – to be excavated in the construction of canals

ORIGINSORIGINS

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UNIVERSE FORMS—13.7 Billion Years Ago—

THE BIG BANG

How Do We Know?How Do We Know?

• The Doppler Effect

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RedshiftRedshift

Absorption lines in the optical spectrum of a supercluster of distant galaxies (right), as compared to absorption lines in the optical spectrum of the Sun (left). Arrows indicate redshift. Wavelength increases up towards the red and beyond (frequency decreases )

The Red ShiftThe Red Shift

• Observed by Edwin Hubble in 1929, the optical spectra ( and red shift) of distant galaxies indicated that galaxies were moving away from Earth and the more distant galaxies were moving faster. The Universe is expanding.

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Expanding UniverseExpanding Universe

• Raisin Bread Analogy

Big Bang TheoryBig Bang Theory

• Evidence for the Big Bang– The “redshift” indicates that the universe is

expanding.• Expansion suggests an origin at a single point.• Rate of expansion indicates explosion at 13.7

billion years ago

– Everywhere is a background radiation of 2.7 K above absolute zero, thought to have originated with the big bang.

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Cosmic Microwave BackgroundPhotons from the earliest days of the universe

Background RadiationBackground Radiation

• Discovered by Arno Penzias and Robert Wilson of Bell Telephone Laboratories

• A pervasive microwave radiation everywhere in the Universe measured as 2.7 Kelvin above absolute zero.

• Thought to be the gradually fading radiation (photons) from the Big Bang; an “afterglow.”

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Big Bang TheoryBig Bang Theory

• Cosmologists do not know the nature of the universe at time zero of the Big Bang.

• Big Bang occurred• Forces followed in the first second

– Gravity (attraction of bodies)– Electromagnetic Force (electricity and magnetism;

holds atoms in molecules)– Strong Nuclear Force (binds protons and neutrons

together)– Weak Nuclear Force (force that causes radioactive

decay)

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Big Bang TheoryBig Bang Theory

• At 300,000 years: Hydrogen, Helium, Light• Next 200 million years stars and galaxies,

chemicals (denser elements) from the death of stars

GALAXIES FORM—12.7 Billion Years Ago—

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12.7 Billion Years AgoFirst Stars and Galaxies

Origin of the Solar SystemOrigin of the Solar System

• Solar Nebula Theory– Solar system formed from collapse of a huge

molecular cloud, a nebula, about 4.6 billion years ago.

– 90% of material condensed into the center of a counterclockwise rotating disk, forming the sun.

– Planetesimals formed from collisions eventually forming planets

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Interstellar MaterialThe most accepted theory of the origin of stars and planetary systems is the collapse of interstellar gas and dust.

Our understanding of the solar nebular theory is that planets form as a by-product of star formation. 1. If the nebula is compressed (overcoming the gas pressure), then gravity may take over and the nebula will collapse inward. 2. As nebular particles come closer together, the gravitational attraction increases (remember the law of gravitation). The increased attraction and collapse results in an increase in temperature. As the cloud collapses, it begins to slowly rotate and flatten into a disk.

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. There are several observations about the solar system that are evidence in favor of the Solar Nebula Theory. 1. All of the planets revolve around the Sun in the same plane (planetary plane). 2. The Sun’s rotational equator lies roughly in the planetary plane.

3. All of the planets revolve around the Sun in the same direction. 4. Planet orbits are nearly circular.

Planets, including EARTH

finish accreting from asteroids – 4.6 BILLION YEARS AGO –

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Formation of PlanetsFormation of Planets

• Inner terrestrial planets formed in high heat and solar winds blew away gases.

• Outer Jovian planets formed with inner core of solids and are composed of gases that condense at low temperatures

• Asteroid belt• Comets

The Hoba Meteorite, in Namibia

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Photo by Howard Edin, American Meteor Society

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COMETS

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MOHO

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Earth as a Dynamic SystemEarth as a Dynamic System

• Division into layers results from variations in– Density (Core=10-13 g/cm3; crust 2.7 g/cm3)– Composition (Fe,Ni; Fe,Mg; Si,Al)– Temperature – Pressure

16 g/cc SOLIDFe, Ni (S, Si)1300 kmInner core

11 g/cc LIQUIDFe, Ni (S, Si)2200 kmOuter core

4.5 g/cc SOLIDMg, Fe, Si, O2900 kmMantle

2.7 g/cc SOLIDSi, O, Al = Granite30-50 kmContinental crust

2.9 g/cc SOLIDSi, O, Fe, Mg, Al= Basalt

3-10 kmOceanic crust

State/DensityCompositionThicknessLayers

Overlaid layers:

Plastic (flows), but SOLID

Portion of mantle

100-350 kmAsthenosphere

RIGID, SOLID, BRITTLE: breaks into plates

100% Crust + Upper Mantle

100-200 kmLithosphere

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EarthEarth’’s Cores Core

• Divided into two parts – Inner solid– Outer liquid

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EarthEarth’’s Mantles Mantle

• Divided into Three Parts– Solid lower mantle– Asthenosphere “mushy”

behaves plastically and generates magma

– Upper mantle is solid and with the crust constitutes the “lithosphere”

MOHO

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EarthEarth’’s crusts crust

• Divided into two types– Continental crust (thicker, more Si rich rocks)– Oceanic crust (thinner, more mafic)

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LithosphericLithospheric PlatesPlates

• Lithosphere is divided into rigid plates

• Plates move on the asthenosphere probably due to convection

• Plates interact to cause earthquakes, mountain building, volcanoes

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LithosphericLithospheric PlatesPlates

• Theory of Plate Tectonics • Plate tectonics and earth systems (p.11,

fig.1.2

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Organic Evolution and the History Organic Evolution and the History of Lifeof Life

• Theory of organic evolution provides framework for study of history of life.

• Integrated with and consistent with Plate Tectonic theory

Organic Evolution and the History Organic Evolution and the History of Lifeof Life

• Fossils– As evidence of organic evolution– As evidence of history of life– As evidence of earth history (Plate Tectonics)

Mesosaur

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Geologic TimeGeologic Time

• Immensity of Geologic time is hard to comprehend

• Time Scale stems from early need to divide Geologic Time into units.

• Advantages of the Time Scale– Sedimentary Rocks and fossils– More refined units

Time ScaleTime Scale

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UniformitarianismUniformitarianism

• James Hutton’s insight into processes and time• Catastrophism and catastrophic events• Rates and Intensities vary in geologic history• Uniformitarianism – “Present is the key to the

past”…Laws of nature have not changed with time….Processes changing and shaping earth are basically the same as in the past….Given enough time, present day processes account for what we see in the rock record.