Transcript relative age dating

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
FOSSILS
• EVIDENCE OF ONCE LIVING ORGANISMS PRESERVED IN
ROCK OR OTHER MEDIA
• HELP TO UNDERSTAND EARTH’S DEVELOPMENTAL
HISTORY
REQUIREMENTS FOR FOSSIL PRESERVATION?
RAPID BURIAL
PROTECTION FROM SCAVENGERS
HARD PARTS
FRIENDLY ENVIRONMENT
• The oldest fossils found indicate life on our planet began
at an age of well over 3 billion years ago.
INTERPRETING GEOLOGIC
HISTORY
• 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 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
DATING 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?
C
B
D
E
F
G
H
I
B
First….
Answer from oldest to youngest;
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•
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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.
UNCONFORMITY
•
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 DATING
= 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
HALF-LIFE TIME IS DIFFERENT FOR EACH
RADIOACTIVE ISOTOPE [*REFERENCE TABLES]
•ALWAYS THE SAME FOR A GIVEN ISOTOPE
•Not affected by Mass, Temperature, Pressure
THE 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 Spreading
1. AGE OF OCEAN FLOOR
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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
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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 BOUNDARY
2. 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 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:
– Climate
– Types of rock
– Slope of Land
– Amount of moisture
– Length of time rock has been weathering