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 (t 1/2 ):  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. 1/2 of the 1/2 = 1/4 the original sample.

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 are left after two half-lives? 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 ridge Continental Crust Ocean 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. divergent 2. convergent 3. transform

-Earth has 6 major plates and many small ones. 1. Eurasian4. North American 2. Pacific5. South American 3. African6. Antarctic

Plate Boundaries 1.Divergent- two plates move apart. Example- seafloor spreading at the Mid-ocean ridge. (6 cm per year)

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 Boundaries 3. Convergent- two plates collide -There are 3 types of plate boundaries

Convergent Plates a.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 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 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