Classroom presentations Classroom presentations to accompany to accompany

Understanding EarthUnderstanding Earth, 3rd edition, 3rd edition

prepared by

Peter Copeland and William Dupré

University of Houston

Chapter 1Chapter 1Building a Planet

Understanding the Earth System

Geology is a science...Geology is a science...

...just like chemistry and physics!

Geologists face the special

challenge of not being able to do

experiments in the sense that

chemists and physicists do.

Scientific principlesScientific principles

The universe is sensible and

governed by immutable rules.

The scientific methodThe scientific method

2) Develop an explanation (hypothesis) that predicts the

outcome of other observations or experiments.

1) Make an observation about the sensible world.

The scientific method (cont.)The scientific method (cont.)

3a) Make new experiments.

3b) Make new observations.

The scientific method (cont.)The scientific method (cont.)

4) Dothe resultsmatch the

predictions of the hypothesis

?

yes

Reject the hypothesis

no

return to step 3

return to step 2

The scientific methodThe scientific method

Simply put:

Always ask yourself, “How will I know if I’m wrong?”

Hypothesis - Theory - LawHypothesis - Theory - Law

A hypothesishypothesis is an explanation initially offered for a set of observations.

When a hypothesis withstands many tests it may be called a theorytheory.

A theory for which it seems there to be no sensible reasons to challenge is called a lawlaw.

A good theory is...A good theory is...

• ParsimoniousParsimonious (is the simplest explanation available)

• ConsilientConsilient(explains a wide range of phenomena)

What are the data used in geology?What are the data used in geology?

Observational: • maps

» rock types, distributions, structures

• microscopic investigations

Experimental:• chemical• geophysical

The problem of experimentsThe problem of experiments

Since geologists are interested in systems that are very big (hundreds of km) and that have evolved over long periods of time (millions of years), they cannot conduct controlled experiments. They must observe the results of Nature’s experiments that are already complete.

UniformitarianisUniformitarianismmThe present is the key to the

past— — James HuttonJames Hutton

Natural laws do not change — however, rates and intensity of processes may.

TIMTIMEE• The big difference between geology

and other sciences: TIME (Geologically speaking, not much happens in a human lifetime!)

• Rates of geologic processes: µm/year to cm/year

• Big earthquakes may displace the ground several meters in a few seconds, but they occur only every 500 years or so.

TIMTIMEE

The rates of geologic

processes are almost always

slower than the rates of human

effects on the environment.

TIMTIMEEThe official SI unit of time is the

second, but it would be very inconvenient to use this unit in geology; even the year is too small in most cases.

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

10 Ma = 10 million years ago

10 m.y. = an interval of time lasting 10 million years

Some Some geologic geologic features take features take millions of millions of years to years to form.form.

Carr Clifton Fig. 1.1

Others take Others take seconds!seconds!

John Sanford/Photo Researchers

Fig. 1.1

Origin of solar systemOrigin of solar systemPick a theory, any theory, but it must be

consistent with these facts:

1) Planets all revolve around the Sun in the same direction in nearly circular orbits.

2) The angle between the axis of rotation and the plane of orbit is small (except Uranus).

3) All planets (except Venus and Uranus) rotate in the same direction as their revolution; their moons do, too.

Origin of solar systemOrigin of solar system4) Each planet is roughly twice as far as the next inner

planet is from the Sun (the Titus-Bode rule).

5) 99.9 % of mass is in the Sun; 99 % of angular momentum is in the planets.

6) Planets in two groups:

• terrestrial (inner): Mercury, Venus, Earth, Mars Mercury is mostly Fe ( = 5.4)

• Jovian (outer): Jupiter, Saturn, Uranus, Neptune. Jupiter mostly gas and ice ( = 0.7) Pluto ????

7) Terrestrial planets are mostly O, Si, Fe, Mg. The Sun is almost entirely H & He (also important in Jovian planets).

Nebular hypothesisNebular hypothesis

Primeval slowly rotating gas cloud(nebula) condensed into severaldiscrete blobs.

fits doesn't fit

rotation angular momentum

mass

Collision hypothesisCollision hypothesisPortions of the Sun were torn off

by a passing star: planetesimals

then collided to form planets.

Problems: gases coming from

Sun would be too hot tocondense; stellar collision

exceedingly rare.

Protoplanet hypothesis Protoplanet hypothesis

• Large gas cloud begins to condense.

• Most mass in the center, turbulence in outer parts.

• Turbulent eddies collect matter meters across; small chunks grow and collide, eventually becoming large aggregates of gas and solid chunks.

• Protoplanets, much bigger than present planets, eventually contracted due to their own gravity.

Fig. 1.2a

Evolution of the Solar SystemEvolution of the Solar System

Fig. 1.2b

Evolution of the Solar SystemEvolution of the Solar System

Fig. 1.2c

Evolution of the Solar SystemEvolution of the Solar System

Fig. 1.2d

Evolution of the Solar SystemEvolution of the Solar System

Fig. 1.3

Our Solar SystemOur Solar System

The The MoonMoon• Only a little smaller than Mercury

(small planet in two-planet system).

• Surface of the moon very different from the surface of Earth.

• No atmosphere, therefore, no weathering.

Formation of the Formation of the MoonMoon

Alfred T. Kamajian Fig. 1.4

Fig. 1.5Extensively modified from D.J. DePaolo, Nature

Timeline for the Timeline for the Sun, Earth, and MoonSun, Earth, and Moon

Why worry about the beginning?Why worry about the beginning?

• The evolutionary course is significantly influenced by the initial state.

• We know the state of the Earth today relatively well; knowing the beginning will help constrain the in between.

A Differentiating A Differentiating PlanetPlanet

Fig. 1.6

Fig. 1.6a

An Early Homogeneous EarthAn Early Homogeneous Earth

Fig. 1.6b

Differentiation Differentiation BeginsBegins

Fig. 1.6c

Relative Abundance of ElementsRelative Abundance of Elements

Fig. 1.7

Fig. 1.9

LithosphereLithosphereHydrosphereHydrosphereAtmosphereAtmosphereBiosphereBiosphere

Fig. 1.8

Interacting Interacting Earth SystemsEarth Systems

Plate tectonicsPlate tectonicsThe unifying concept of The unifying concept of

the Earth sciences.the Earth sciences.

• The outer portion of the Earth is made up of about 20 distinct “plates” (~ 100 km thick) that move relative to each other.

• This motion is what causes earthquakes and forms mountain ranges.

Plate tectonicsPlate tectonics• lithospherelithosphere: the outer rigid

shell of the earth (~ 100 km). The plates are composed of this material.

• asthenosphereasthenosphere: part of mantle beneath lithosphere.

• The lithosphere rides ON TOP of the asthenosphere.

Earth’s Crust, Lithosphere, Earth’s Crust, Lithosphere,

and Asthenosphereand Asthenosphere

Fig. 1.11

Present-day PlatesPresent-day Plates

Pete W. Sloss, NOAA-NESDIS-NGDC Fig. 1.12

Fig. 1.13a

Convection Convection in the Kitchenin the Kitchen

Fig. 1.13b

Convection in the Earth

Three types of plate boundariesThree types of plate boundaries

1. Divergent

2. Convergent

3. Strike-slip

(transform,conservative)

Three Types of Plate BoundariesThree Types of Plate Boundaries

Fig. 1.14

Fig. 1.14a

Fig. 1.14b

Peter W. Sloss, NOAA-NESDIS-NGDC

Mid-AtlanticRidge

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

Gudmundur E. Sigvaldason,Nordic Volcanological Institute Fig. 1.15

John Sheldon Fig. 1.17

San Andreas FaultSan Andreas Fault

Fig. 1.16

The rejection and acceptance The rejection and acceptance of Continental Driftof Continental Drift

• First suggested by Alfred Wegener in 1912.

• Rejected by most geologists.

• New data after WWII led to the “plate tectonic revolution” in 1960’s.

• Now embraced by essentially everybody.

• Today’s geology textbooks radically different than those of 40 years ago.

The Supercontinent of PangaeaThe Supercontinent of Pangaea(200 million years ago)(200 million years ago)

Fig. 1.18

Present-day PlatesPresent-day Plates

Pete W. Sloss, NOAA-NESDIS-NGDC Fig. 1.12

Caution: Geologist at WorkCaution: Geologist at Work

David R. Frazier/ Photo Researchers Fig. 1.19