historical geology origins

7/30/2019 Historical Geology Origins

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HISTORICAL GEOLOGYHISTORICAL GEOLOGY

Earth is a Dynamic andEarth 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 earthand life.

Placing events in order

Explaining how and why events took place

Plate Tectonics: Earths outermost part is composed of aseries of moving plates whose interactions have affected the

planets physical and biological history.

Organic Evolution

Geologic Time

PLATE TECTONICS


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The study of the origin and evolution of theearth and life. Placing events in order

Explaining how and why events took place Plate Tectonics

Organic Evolution: Earths biota has evolved orchanged throughout its history.

Geologic Time

ORGANIC EVOLUTION


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The study of the origin and evolution of the earthand 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 periodsof time.


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The study of the origin and evolution of theearth 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 ofHistorical Geology are derived from datagathered 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 ofunconformities


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In historical geology we study changes in our dynamic planet

how and why past events happened

implication for todays global ecosystems

Principles of historical geology not only aid in interpreting Earths history

but also have practical applications

William Smith, an Englishsurveyor/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 FORMS13.7 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 asupercluster of distant galaxies (right), ascompared to absorption lines in the opticalspectrum of the Sun (left). Arrows indicateredshift. Wavelength increases up towardsthe red and beyond (frequency decreases )

The Red ShiftThe Red Shift Observed by Edwin Hubble in 1929, the

optical spectra ( and red shift) of distantgalaxies indicated that galaxies weremoving away from Earth and the moredistant galaxies were moving faster. TheUniverse 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 13.7billion years ago

Everywhere is a background radiation of 2.7 Kabove absolute zero, thought to haveoriginated 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 radiationeverywhere in the Universe measured as2.7 Kelvin above absolute zero.

Thought to be the gradually fading

radiation (photons) from the Big Bang; anafterglow.


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Cosmologists do not know the nature of theuniverse 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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At 300,000 years: Hydrogen, Helium, Light

Next 200 million years stars and galaxies,chemicals (denser elements) from thedeath of stars

GALAXIES FORM12.7 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 hugemolecular cloud, a nebula, about 4.6 billionyears ago.

90% of material condensed into the center ofa counterclockwise rotating disk, forming thesun.

Planetesimals formed from collisionseventually forming planets


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Interstellar Material

The most accepted

theory of the origin ofstars 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 starformation.

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 collapseresults 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 Suns 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,includingEARTH

finish accretingfrom asteroids 4.6 BILLIONYEARS AGO


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Formation of PlanetsFormation of Planets

Inner terrestrial planets formed in highheat and solar winds blew away gases.

Outer Jovian planets formed with innercore of solids and are composed of gasesthat 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 variationsin

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 kmContinentalcrust

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

= Basalt

3-10 kmOceanic

crust

State/DensityCompositionThicknessLayers

Overlaid layers:

Plastic (flows),but SOLID

Portion ofmantle

100-350 kmAsthenosphere

RIGID, SOLID,

BRITTLE:breaks intoplates

100% Crust +

Upper Mantle

100-200 kmLithosphere


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EarthEarths Cores Core Divided into two parts

Inner solid

Outer liquid


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EarthEarths Mantles Mantle

Divided into ThreeParts

Solid lower mantle

Asthenosphere mushybehaves plastically andgenerates magma

Upper mantle is solid

and with the crustconstitutes thelithosphere

MOHO


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EarthEarths crusts crust

Divided into two types

Continental crust (thicker, more Si rich rocks)

Oceanic crust (thinner, more mafic)


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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 HistoryOrganic Evolution and the History

of Lifeof Life Theory of organic evolution provides

framework for study of history of life.

Integrated with and consistent with PlateTectonic theory

Organic Evolution and the HistoryOrganic 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 tocomprehend

Time Scale stems from early need todivide 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 Huttons insight into processes and time

Catastrophism and catastrophic events

Rates and Intensities vary in geologic history

Uniformitarianism Present is the key to thepastLaws of nature have not changed withtime.Processes changing and shaping earthare basically the same as in the past.Given

enough time, present day processes account forwhat we see in the rock record.

historical geology origins

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