Lecture 2:Lecture 2:Understanding EarthUnderstanding Earth

The Science of GeologyThe Science of Geology

Geology - the science that pursues an Geology - the science that pursues an understanding of planet Earth understanding of planet Earth

Physical geologyPhysical geology - examines the - examines the materials composing Earth and seeks materials composing Earth and seeks to understand the many processes that to understand the many processes that operate beneath and upon its surface operate beneath and upon its surface

Historical geologyHistorical geology - seeks an - seeks an understanding of the origin of Earth understanding of the origin of Earth and its development through time and its development through time

The Science of GeologyThe Science of Geology

The Nature of Scientific InquiryThe Nature of Scientific Inquiry

How or why things happen is explained How or why things happen is explained using a using a

Hypothesis Hypothesis – a tentative (or untested) – a tentative (or untested) explanation explanation

TheoryTheory – a well-tested and widely – a well-tested and widely accepted view that the scientific accepted view that the scientific community agrees best explains certain community agrees best explains certain observable facts observable facts

Evolution of Solar SystemEvolution of Solar System

Nebular hypothesisNebular hypothesis Rotating cloud called the solar nebulaRotating cloud called the solar nebula Nebula began to contract about 5 billion years agoNebula began to contract about 5 billion years ago 99.9 % of mass is in the Sun (composed mainly of 99.9 % of mass is in the Sun (composed mainly of

hydrogen and helium) hydrogen and helium)

Planets in two groups:Planets in two groups:• Inner planetsInner planets (Mercury, Venus, Earth, Mars) begin to form (Mercury, Venus, Earth, Mars) begin to form

from metallic and rocky substances. They are mostly O, from metallic and rocky substances. They are mostly O, Si, Fe, Mg.Si, Fe, Mg.

• Larger outer planetsLarger outer planets (Jupiter, Saturn, Uranus, Neptune) (Jupiter, Saturn, Uranus, Neptune) began forming from fragments of ices (Hbegan forming from fragments of ices (H22O, COO, CO22,, and and others) and gases.others) and gases.

Evolution of the Solar SystemEvolution of the Solar System

Evolution of the Solar SystemEvolution of the Solar System

Evolution of the Solar SystemEvolution of the Solar System

Evolution of the Solar SystemEvolution of the Solar System

The Solar SystemThe Solar System

A view of EarthA view of Earth

Earth is a planet that is small and self-Earth is a planet that is small and self-containedcontained

Earth’s four spheres Earth’s four spheres HydrosphereHydrosphere AtmosphereAtmosphere BiosphereBiosphere Solid EarthSolid Earth

Earth Internal StructureEarth Internal Structure

Layers defined by composition Layers defined by composition CrustCrust MantleMantle CoreCore

Layers defined by physical propertiesLayers defined by physical properties LithosphereLithosphere AsthenosphereAsthenosphere MesosphereMesosphere Inner and Outer CoreInner and Outer Core

Earth’slayeredstructure

The face of EarthThe face of Earth

Earth’s surface Earth’s surface ContinentsContinents OceansOceans

ContinentsContinents Mountain beltsMountain belts• Most prominent feature of continentsMost prominent feature of continents

The stable interiorThe stable interior• Composed of Composed of shieldsshields and stable and stable platformsplatforms

The ContinentsThe Continents

The face of EarthThe face of Earth

Ocean basinsOcean basins Oceanic ridge systemOceanic ridge system• Most prominent topographic feature on Most prominent topographic feature on

EarthEarth• Composed of igneous rock that has been Composed of igneous rock that has been

fractured and uplifted fractured and uplifted

Oceanic Ridge SystemOceanic Ridge System

Dynamic EarthDynamic Earth

The theory of The theory of plate tectonicsplate tectonics Involves understanding the workings of Involves understanding the workings of

our dynamic planet our dynamic planet Began in the early part of the twentieth Began in the early part of the twentieth

century with a proposal called century with a proposal called continental drift – the idea that continental drift – the idea that continents moved about the face of the continents moved about the face of the planet planet

Dynamic EarthDynamic Earth

The theory of plate tectonicsThe theory of plate tectonics Theory, called Theory, called plate tectonics,plate tectonics, has now has now

emerged that provides geologists with emerged that provides geologists with the first comprehensive model of Earth’s the first comprehensive model of Earth’s internal workings internal workings

Plate boundariesPlate boundaries All major interactions among individual All major interactions among individual

plates occurs along their boundariesplates occurs along their boundaries

Tectonic PlatesTectonic Plates

Dynamic EarthDynamic Earth

Plate boundariesPlate boundaries Divergent boundaryDivergent boundary – two plates – two plates

move apart, resulting in upwelling of move apart, resulting in upwelling of material from the mantle to create material from the mantle to create new seafloor new seafloor

Convergent boundaryConvergent boundary – two plates – two plates move together with subduction of move together with subduction of oceanic plates or collision of two oceanic plates or collision of two continental platescontinental plates

Iceland is being Iceland is being pulled apart as it sits pulled apart as it sits astride the Mid-astride the Mid-Atlantic RidgeAtlantic Ridge..

San San Andreas Andreas

FaultFault

Dynamic EarthDynamic Earth

Plate boundariesPlate boundaries Transform boundaries -Transform boundaries - located where located where

plates grind past each other without plates grind past each other without either generating new lithosphere or either generating new lithosphere or consuming old lithosphere consuming old lithosphere

Changing boundariesChanging boundaries - new plate - new plate boundaries are created in response to boundaries are created in response to changes in the forces acting on the changes in the forces acting on the lithosphere lithosphere

Geologic timeGeologic time

The magnitude of geologic time Involves vast The magnitude of geologic time Involves vast times – millions or billions of yearstimes – millions or billions of years

An appreciation for the magnitude of An appreciation for the magnitude of geologic time is important because many geologic time is important because many processes are very gradualprocesses are very gradual

The big difference between geology and The big difference between geology and other sciences: TIME (Geologically speaking, other sciences: TIME (Geologically speaking, not much happens in a human lifetime!)not much happens in a human lifetime!)

Therefore, geologists use millions of years Therefore, geologists use millions of years as the standard unit of timeas the standard unit of time

Age of EarthAge of Earth

~ 4,600 million years~ 4,600 million years Radioactive mineralsRadioactive minerals• Radium, uranium, lead Radium, uranium, lead

Salts in the oceans and its Salts in the oceans and its accumulation (not accurate)accumulation (not accurate)

Fro younger ages, deposits and CFro younger ages, deposits and C1414

Thegeologic

timescale