Geo Science Ch. 17
Tectonic Plates
huge pieces of crust and rigid upper mantle that fit together at their edges to cover Earth's surface
Isochron
imaginary line on a map that shows points of the same age- that is they formed at the same time.
Divergent Boundary
regions where two tectonic plates are moving apart
Climatic evidence- fossils of the Glossoptoris had been found on many parts of the Earth, including South America, Antarctica, and India. The area separating the fossils was too large to have had a single climate, the fossils had been close to the equator, therefore the continents were closer together.
Explain in detail one of the pieces of evidence
More than 11km deep
How deep is the Mariana Trench?
4.5 billion years old
How old is the earth?
Normal polarity is when a magnetic field that has the same orientation as Earth's present field, while reversed polarity is opposite to the present field
What is the difference between magnetic fields of normal polarity and reversed polarity?
It is heated unevenly by radioactive decay
What provides heat to the mantle?
What forces could cause the movement? How could continents move through solids?
What questions did scientists ask regarding Wegeners' theory?
1.The age of the ocean floor is very young 2. The rocks ages vary and are predictable
What two discoveries did rock samples from the ocean floor lead to?
Magnetic reversal
an event that causes a magnetic field to reverse direction
Slab Pull
tectonic process associated with convection currents in Earth's mantle that occurs as the weight of the subducting plate pulls the trailing lithosphere into a subduction zone
Ridge Push
tectonic process associated with convection currents in Earth's mantle that occurs when the weight of an elevated ridge pushes an oceanic plate toward a subduction zone
Pangea
term for the super continent which contained all the plates together
convergent boundary
A plate boundary where two plates move toward each other.
Transform Boundary
A region where two plates slide horizontally past each other
Evidence from Rock Foundation- Wegener observed that many layers of rocks in the Appalachian Mountains in the U.S. were identical to layers of rocks in similar mountains in Greenland and Europe. These similar groups of rocks, older than 200 million years, supported Wegener's idea that the continents had once been joined.
Explain in detail one of the pieces of evidence
Seafloor spreading is the theory that explains how new ocean crust is formed at ocean ridges and destroyed in ocean trenches. During this process, magma, which is less dense and hotter than surrounding mantle material, is forced towards the surface of the crust along the ocean ridge. The two sides of the ridge spread apart, magma fills the gap that was created, when the magma solidifies, a small amount of new ocean floor is added, and as seafloor spreading along the ocean ridge continues more magma is forced upward and solidifies.
Explain the process of seafloor spreading
By matching the magnetic patterns on the seafloor with the known pattern of magnetic reversal on land, scientists were able to determine the age of the ocean floor from magnetic recording and to create isochron maps of the ocean floor.
How did scientists determine the age of the ocean floor?
1. continents fit like puzzle 2.evidence from fossils 3. evidence from rock formation 4.climate evidence 5. Coal deposits 6. Glaciers
List the Six Pieces of Evidence that support Wegener's Theory
1. North American Plate 2. South American Plate 3. African Plate 4. Eurasian Plate 5.Antarctic Plate 6. Indo-Australia Plate 7. Pacific Plate 8. Nazca Plate
List the eight major tectonic plates
Outer crust, inner crust, mantle, core
List the layers of the Earth from the outside to the inside
Paleomagnetism
The study of the history of Earth's magnetic field
Convection
The transfer of heat by the movement of a fluid
Continents were separated by earthquakes and floods
Wegener's Theory- What does it propose?
There was lots of scientific evidence to back it up
Wegener's Theory- Why is it considered a scientific theory?
continental drift
Wegner's Theory- What is it called?
vast underwater mountain chains
What are ocean ridges?
The flow of molten iron in the outer core
What generates Earth's magnetic field?
A magnometer is a device that can detect small changes in magnetic fields.
What is a magnometer?
Large Mountain ranges
What usually results from a continental-continental convergent boundary?
Divergent Boundaries form a rift valley on land, and they form new oceanic crust and ridges in the ocean
What usually results from a divergent boundary on land or in an ocean?
Faults, offset roads, fences and land.
What usually results from a transform boundary?
A mountain range with many volcanoes
What usually results from an oceanic-continental convergent boundary?
An arc of volcanic islands that parallel the trench.
What usually results from an oceanic-oceanic convergent boundary?
Subduction
When two plates collide, the denser plate eventually descends below the other, less- dense plate.
Along a convection current a plate boundary must lift and split to become a divergent boundary, and to make a convergent boundary, there is a sinking force that pulls tectonic plates downward.
Where along a convection current must a plate boundary occur to cause (a) divergent boundary and (b) a convergent boundary?
An oceanic plate
Which is usually more dense- an oceanic or continental plate?
There is no melting in the process, so there are no volcanoes
Why aren't there volcanoes associated with continental-continental convergent boundaries?
Because of the two unanswered questions, his theory was rejected.
Why did scientists reject Wegener's theory?