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 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

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! Examples:

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

Living: Carbon 14 Carbon 12

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 1You 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

half-lives?

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

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

2. Original Horizontality- soil is deposited horizontally (fall to bottom) then form rock layers

3. Lateral Continuity- layers of sediment extend in all directions when they form

4. Law of Cross-Cutting Relationships- Folds and faults are younger than the layers that they cut across

5. Inclusions- the inclusions (rock pieces) are older than the surrounding rock

6. Faunal Succession- fossils can be used to identify relative age of layers of rock

-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

Believed in the theory called “continental drift”

The supercontinent (Pangea) split into pieces, then moved to different positions

Support 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

continent

old

Mid-ocean ridge

young old

Seafloor & trench

continent

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 ridgeContinental

Crust

Ocean CrustOcean Crust

Continental

Crust

lithosphere

Convection

Current

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!

Plate Tectonics Theory

There are 3 types of plate boundaries:1. divergent2. convergent3. 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 Boundaries1. Divergent- two plates move apart.

Example- seafloor spreading at the Mid-ocean ridge. (6 cm per year)

Plate Boundaries2. Transform- plates move past one another in opposite directions or in the same direction at different speeds

Example- San Andreas fault

Plate Boundaries

3. Convergent- two plates collide

-There are 3 types of plate boundaries

Convergent Platesa.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 Platesb. Oceanic and continental plates collide- the denser oceanic plate descends into the athenosphere.

- may form chain of volcanic mountains

- Earthquakes are common

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)

Convection Currents

HOT Spots

Stationary plumes of hot material that initiate at the core/mantle interface

Hawaii: the plume is beneath oceanic crust

Hot Spots

Yellowstone is associated with a hot spot under continental crust

Hot Spots