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Record in the Rock. What Processes Shape our Earth?. Earth Science- the study of earth and space Importance of Earth Science: Contributes to our knowledge of the world Understanding forces that shape our earth can better forecast potential disasters Provides valuable resources

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record in the rock

Record in the Rock

What Processes Shape our Earth?

Earth Science- the study of earth and space

Importance of Earth Science:

  • Contributes to our knowledge of the world
  • Understanding forces that shape our earth can better forecast potential disasters
  • Provides valuable resources
  • Makes life better through application of technology
layers of the earth
Layers of the Earth
  • Characterized by a gradual increase in temperature, pressure, and density with depth
    • Inner Core: solid; composed mainly of nickel and iron
    • Outer Core: hot liquid made of nickel and iron
    • Mantle: thick layer; plasma; denser than crust
    • Crust: thin layer of silicates; two kinds of crusts-
      • Oceanic Crust: Older, thicker, less dense, granite
      • Continental Crust: Thin, younger, denser, basalt
Lithosphere: crust and upper part of the mantle (plate)

Asthenosphere: part of mantle; less rigid than the lithosphere; convection currents flow here

age of the earth
Age of the Earth
  • Kelvin Method:
    • Assumed earth was hot molten rock
    • he measured rate of earth’s cooling to present
    • Took into account heat coming from the sun and from within the earth
      • Problem: was not aware of radioactivity
    • Measured radioactive decay of Uranium 238  Lead 206
    • Estimated Earth as 4.6 Billion Years old
radiometric dating
Henri Bequerel discovered the radioactive element

Radioactive Decay: when elements break down

Radiometric Dating: rate at which radioactive decay takes place

Based on half-life (time to take ½ of element to decay)

Radioactive decay rates don’t change!


Nonliving: 3.9 billion year old rock of Uranium 238  Lead 206

Living: Carbon 14  Carbon 12

Radiometric Dating
radioactive half life t 1 2
Radioactive Half-Life (t1/2 ):
  • The time for half of the radioactive substances in a given sample to undergo decay.
  • After one half life there is 1/2 of original sample left.
  • After two half-lives, there will be

1/2 of the 1/2 = 1/4 the original sample.

example 1
Example 1

You have 100 g of radioactive C-14. The half-life of C-14 is 5730 years.

  • How many grams are left after one half-life?
  • Answer:50 g
  • How many grams

are left after two


example 2
Example 2
  • The half-life of iodine-131 is 8 days.
  • If you start with 36 grams of I-131, how much will be left after 24 days?
  • 36 g  1 half-life  8 days  18 g
  • 18 g  2 half-lives  16 days  9 g
  • 9 g  3 half-lives  24 days  4.5 g
types of relative dating
Relative Dating: Finding the age of something compared to something else

Law of Superposition- the bottom layer of an undisturbed section is older than the top

Types of Relative Dating
2. Original Horizontality- soil is deposited horizontally (fall to bottom) then form rock layers
4. Law of Cross-Cutting Relationships- Folds and faults are younger than the layers that they cut across
-Index Fossil-

1. lived in a certain time span in many places

2. lived in great numbers

3. distinct features to identify

-Correlation- matching rocks by Index Fossil in different places

alfred wegener
Alfred Wegener
  • Believed in the theory called “continental drift”
  • The supercontinent (Pangea) split into pieces, then moved to different positions
  • a system of under water mountain chains or mid-ocean ridges, rise thousands of meters above the ocean floor.
  • Youngest ocean floor rocks-near the mid-ocean ridge.
  • Oldest near the edges of the ocean basins
  • When the seafloor reaches a continental boundary, it is forced downward beneath the continent called the seafloor trench






Seafloor & trench

Mid-ocean ridge

plate tectonics
Plate Tectonics
  • Plates- crust that extends into the upper part of the mantle.
  • Upper part of the mantle is called the lithosphere.
  • The bottom part of the lithosphere that is a plastic like zone is called the asthenosphere.

Mid-ocean ridge





Ocean Crust

Ocean Crust





Plate Tectonics Theory

A relatively recent theory that the Earth's crust is composed of rigid plates that move relative to one another.

Plate movements are on the order of a few centimeters/year - about the same rate as your fingernails grow!

There are 3 types of plate boundaries:

1. divergent

2. convergent

3. transform


-Earth has 6 major plates and many small ones.

1. Eurasian 4. North American

2. Pacific 5. South American

3. African 6. Antarctic

plate boundaries
Plate Boundaries
  • Divergent- two plates move apart.
    • Example- seafloor spreading at the Mid-ocean ridge. (6 cm per year)
plate boundaries1
Plate Boundaries

2. Transform- plates move past one another in opposite directions or in the same direction at different speeds

Example- San Andreas fault

plate boundaries2
Plate Boundaries

3. Convergent- two plates collide

-There are 3 types of plate boundaries

convergent plates
Convergent Plates
  • Two ocean plates collide- the edge of one is bent downwards.
    • Regions where the plates descend are called subduction zone
    • May form volcanoes or islands (island arc)
convergent plates1
Convergent Plates

b. Oceanic and continental plates collide- the denser oceanic plate descends into the athenosphere.

- may form chain of volcanic mountains

- Earthquakes are common

convergent plates2
Convergent Plates

c. Two continental plates collide- the continental rocks buckle and rise.

- mountain chains form

- earthquakes are common

- very little volcanic activity

-continental motion

occurs (1-5 cm per year)

hot spots
HOT Spots
  • Stationary plumes of hot material that initiate at the core/mantle interface
  • Hawaii: the plume is beneath oceanic crust
hot spots1
Hot Spots
  • Yellowstone is associated with a hot spot under continental crust