Upload
jody-norman
View
225
Download
1
Tags:
Embed Size (px)
Citation preview
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