Earth’s Composition and Structure

What you need to know!• Students know how successive rock strata and fossils can be used to

confirm the age, history, and changing life forms of the Earth, including how this evidence is affected by the folding, breaking, and uplifting of layers. E/S

• Students understand the concept of plate tectonics including the evidence that supports it (structural, geophysical and paleontological evidence). E/S

• Students know elements exist in fixed amounts and move through solid earth, oceans, atmosphere and living things as part of biogeochemical cycles. E/S

• Students know processes of obtaining, using, and recycling of renewable and non-renewable resources. E/S

• Students know soil, derived from weathered rocks and decomposed organic material, is found in layers. E/S

Rocks

FOSSILSFOSSILS

• EVIDENCE OF ONCE LIVING ORGANISMS PRESERVED IN ROCK OR OTHER MEDIA

• HELP TO UNDERSTAND EARTH’S DEVELOPMENTAL HISTORYREQUIREMENTS FOR FOSSIL PRESERVATION?

RAPID BURIALPROTECTION FROM SCAVENGERSHARD PARTSFRIENDLY ENVIRONMENT

• The oldest fossils found indicate life on our planet began at an age of well over 3 billion years ago.

INTERPRETING GEOLOGIC INTERPRETING GEOLOGIC HISTORYHISTORY

• GEOLOGIC HISTORY IS RECORDED IN THE ROCK RECORD – OBSERVATIONS OF COMPOSITION, STRUCTURE, POSITION, AND FOSSIL CONTENT LEADS TO INTERPRETATIONS OF THE GEOLOGIC HISTORY OF EARTH.

– RELATIVE AGE DATINGRELATIVE AGE DATING OF ROCKS AND EVENTS• Used to determine the order of events and relative

age of rocks by examining the position of rocks in a sequence

• UNIFORMITARIANISM

Earth’s History

RULES FOR RELATIVE AGE RULES FOR RELATIVE AGE DATING OF ROCK FEATURESDATING OF ROCK FEATURES

• PRINCIPLE OF SUPERPOSITION– OLDEST ROCKS ON BOTTOM

• PRINCIPLE OF ORIGINAL HORIZONTALITY– DEPOSITED AS HORIZONTAL LAYERS OF SEDIMENTS

• PRINCIPLE OF INCLUSIONS– ROCK MUST BE OLDER THAN LAYER FOUND IN

• PRINCIPLE OF CROSS-CUTTING RELATIONS– GEOLOGIC FEATURES YOUNGER THAN LAYER IT CUT

• EXAMPLES?

Can you list the order of events?

First….

B

B

C

DE

F

GH

I

Answer from oldest to youngest;

• 1. Conglomerate (I) • 2. Shale (H)• 3.Sandstone (G) • 4. Siltstone (F)• 5. Limestone (E)• 6. Breccia (using the Principle

of Superposition) (D)• 7. Basalt Intrusion (and contact

metamorphism) (B then A)• 8. Fault (using the Principle of

Cross Cutting Relations) (C)• 9. Erosion.

UNCONFORMITYUNCONFORMITY

• Gaps in the rock record that develop when agents of erosion remove existing rock layers

Three types

1. Angular Unconformity

2. Disconformity

3. Nonconformity

ABSOLUTE AGE DATINGABSOLUTE AGE DATING

HALF-LIFE TIME IS DIFFERENT FOR EACH RADIOACTIVE ISOTOPE [*REFERENCE TABLES]

•ALWAYS THE SAME FOR A GIVEN ISOTOPE•Not affected by Mass, Temperature, PressureMass, Temperature, Pressure

= A METHOD USED TO DETERMINE THE AGE, IN YEARS, OF A ROCK OR OTHER OBJECT

HALF-LIFE = THE TIME IT TAKES FOR HALF OF THE ATOMS IN THE ISOTOPE TO DECAY

THE DYNAMIC CRUSTTHE DYNAMIC CRUST• THE DEVELOPMENT OF A THEORY

– CONTINENTAL DRIFT – Alfred Wegener (1912)– SEA-FLOOR SPREADING – Harry Hess (1960’s)– PLATE TECTONICS – Late 1960’s

CONTINENTAL DRIFT

• JIGSAW PUZZLE-LIKE FIT• GEOLOGIC EVIDENCE

– AGE AND ROCK TYPE SIMILAR

• CORRELATION OF FOSSILS– MESOSAURUS,

GLOSSOPTERIS…• CHANGES IN CLIMATE

PATTERN

Evidence for Seafloor Spreading1. AGE OF OCEAN FLOOR

• 1968 Glomar Challenger collected rocks from seafloor• No rocks older than 180 million years found!• Youngest rocks found at mid-ocean ridges• Rocks became increasingly older farther from the ridge

2. MAGNETISM RECORDED IN BASALT SHOWED REVERSALS OF EARTH’S MAGNETIC POLARITY

• Scientists used a magnetometer to investigate the magnetic alignment of the rocks

• Found many magnetic reversals

PLATE TECTONICS• ATTEMPTS TO EXPLAIN

CRUSTAL CHANGES IN TERMS OF THE CREATION, MOTION, AND DESTRUCTION OF LARGE SECTIONS OF THE LITHOSPHERE (PLATES)

1. DIVERGENT BOUNDARY2. CONVERGENT BOUNDARY 3. TRANSFORM BOUNDARY

Material on Earth• The elements that are present on Earth today are

the same elements that were present 4.6 billion years ago.

• Earth’s processes, driven by energy transfer, provide the mechanisms that allow for the circulation of these elements that exist in relatively fixed quantities. Biogeochemical cycles describe the movement (or cycling) of matter through Earth’s systems.

• In general the systems can be subdivided, for ease of examination, into the atmosphere, hydrosphere, lithosphere, and biosphere.

Biogeochemical cycles account

for the movement of

matter throughout the environment.

Renewable vs. nonrenewable resources

Two Types of WeatheringTwo Types of Weathering

I. Mechanical (or Physical) Weathering (M.W.) Breakdown of rocks into sediments without

chemical change.

II. Chemical Weathering (C.M.) Breakdown of rocks by chemical action, results in change of

mineral composition.

SOIL PROFILE• Each layer in the soil

profile is called a horizon• Mature soil profiles

contain three horizons (A, B, and C)

• Soil formation from bedrock, the parent material, take a tremendous amount of time.

• The time is controlled by the amount of weathering.

• Weathering is controlled by the type of climate.

Evolution of Soil Horizons

Factors Affecting Soil Formation:Factors Affecting Soil Formation:

– Climate

– Types of rock

– Slope of Land

– Amount of moisture

– Length of time rock has been weathering