Science Chapter 4 and 6 Flashcards
Continental Drift
Wegener proposed the hypothesis of ___________, which suggested that continents are in constant motion on the surface of Earth.
Pangaea
- Nearly 100 years ago, Alfred Wegener proposed that all the continents were once part of a supercontinent called ________.
- Over time, ________ began breaking apart and the continents slowly moved to their present position.
How did Wegener formulate his theory of continental drift?
•Wegener observed the similarities of continental coastlines now separated by oceans and how they could fit together like pieces of a puzzle. •Evidence to support Wegener’s hypothesis is found in
•climate clues;
•fossil clues;
•rock clues.
Evidence That Continents Move
•When Wegener pieced Pangaea together, he proposed that the continents were located closer to the South Pole 250 million years ago.
•Wegener suggested that a large sheet of ice covered the continents.
•Wegener studied the sediments left behind and the glacial grooves that formed when the ice sheets melted and Pangaea spread apart.
•This provided climate evidence for continental drift.
Evidence that continents move.
•Animals and plants that live on separate continents can be unique to that continent alone.
•Fossils of similar organisms have been found on several continents separated by oceans.
•Fossils of a plant called Glossopteris have been found on continents that are now separated by oceans.
mountain ranges and rock formations on different continents had common origins, providing rock evidence for continental drift.
•Volcanic rock that is identical in chemistry and age has been found on both the western coast of Africa and the eastern coast of South America.
How long was it until Wegener’s ideas were widely accepted?
Four decades
Why didn’t scientists accept the theory of continental drift?
- Scientists questioned continental drift because it was a slow process and Wegener could not measure how fast continents moved or how they moved.
- Scientists could not understand how continents could push their way through the solid rock of the mantle and the seafloor.
While pole was Australia, Antarctica, South America, and India closer to?
The South Pole.
How did scientists determine the topography of the ocean floor?
During the late 1940s scientists were able to determine the depth of the ocean using a device called an echo sounder.
Mid-ocean ridge
•Once ocean depths were determined, scientists used these data to create a topographic map of the sea floor that revealed vast mountain ranges, called mid-ocean ridges, that stretch for many miles deep below the ocean’s surface.
Seafloor spreading
Seafloor spreading is the process by which new oceanic crust forms along a mid-ocean ridge and older oceanic crust moves away from the ridge.
The process of sea floor spreading
When the seafloor spreads, the mantle below melts and forms magma.
•Magma erupts on Earth’s surface as lava, which cools and crystallizes on the seafloor, forming rock.
•Because the lava erupts into water, it cools rapidly and forms rounded structures called pillow lavas.
•As the seafloor continues to spread apart, the older oceanic crust moves away from the mid-ocean ridge.
How many ways can the ridges form?
The rugged mountains that make up the mid-ocean ridge system can form in two different ways.
What are two ways mid-ocean ridges can form?
•Large amounts of lava can erupt from the center of the ridge, cool, and build up around the ridge.
*pillow lava
Or, as the lava cools and forms new crust, it cracks and the rocks move up or down along these cracks in the seafloor, forming jagged mountain ranges.
Abyssal plain
the smooth part of the seafloor, is made when the layer of sediment that accumulates far from the mid-ocean ridge becomes thick enough
Normal polarity
a state in which magnetized objects, such as compass needles, will orient themselves to point north.
What evidence did scientists find evidence to support sea floor spreading?
- The first evidence used to support seafloor spreading was discovered in rocks on the seafloor.
- Scientists studied the magnetic signature of minerals in these rocks.
Magnetic reversal
the magnetic field reverses direction.
Reversed polarity
•The opposite of normal polarity is reversed polarity: a state in which magnetized objects reverse direction and orient themselves to point south.
What do rocks have to do with mid-ocean ridges?
•Volcanic rock on the seafloor contains iron-rich minerals that are magnetic.
•Magnetic minerals in cooling lava from the mid-ocean ridge record the direction of Earth’s magnetic field.
•Scientists have discovered parallel patterns in the magnetic signature of rocks on either side of a mid-ocean ridge.
Minerals in fresh lava record Earth’s magnetic signature.
How did the scientists study the magnetic materials in rocks?
•Scientists studied magnetic minerals in rocks from the seafloor using a magnetometer to measure and record the magnetic signature.
What did the scientists discover on either side of the mid-ocean ridge?
They discovered parallel magnetic stripes on either side of the mid-ocean ridge.
•Each pair of stripes has a similar composition, age, and magnetic character.
•The pairs of magnetic stripes confirm that the ocean crust formed at mid-ocean ridges is carried away from the center of the ridges in opposite directions.
Evidence of sea floor spreading
•Other measurements made on the seafloor confirm seafloor spreading.
•Measuring the amount of thermal energy leaving the Earth shows that more thermal energy leaves Earth near mid-ocean ridges than is released from beneath the abyssal plains.
Sediment collected from the seafloor can be dated to show that the sediment closest to the mid-ocean ridge is younger than the sediment farther away from the ridge.
Nearly how many years ago did Alfred Wegener start an important investigation, and what was he trying to find?
Nearly 100 years ago, and whether earth’s continents were in a fixed position.
Was Wegener the first to notice the puzzle-like continents?
No, he was just the first to propose his theory.
What is fossil evidence of continental drift?
A plant fossil called glossopteris is found on several continents that are separated by sea.
What kind of climate did Antarctica used to have?
Antarctica had a warm and wet climate.
What are some rock clues to suggest continental drift?
Mountain ranges and rock formation looked like they had similar origins. Volcano eruptions appear to have gone off at about the same time on the west coast of Africa, and the east coast of South America.
Why were scientists skeptical of Wegener’s hypothesis?
They were skeptical because he couldn’t come up with a reason for the movement of the continents.
How did Wegener support his theory using climate clues?
Wegener found glacial grooves on South America, Africa, India, and Antarctica.
How did scientists determine the topography of the bottom of the ocean?
By using an echo-sounder.
Are mountain ranges taller on land, or under the sea?
Mountain ridges in the ocean stretch longer.
What happens as the Seafloor continues to spread apart?
The older oceanic crust moves away from the ridge.
What does the lava that comes out of the ridge cool as?
Basalt
What causes continental drift.
Seafloor spreading
Where does sediment accumulate?
In ocean basins
When do magnetic reversals occur?
Every few hundred thousand to million years.
What does basalt contain, and what does it do?
Iron rich minerals. They act as magnets, recording the polarity of earth at the time.
How else did scientists prove Seafloor spreading?
They drilled a hole, and sediment from the Seafloor can be dated.
Isostasy
The equilibrium between continental crust and the denser mantle below it.
Subsidence
The downward vertical motion of Earth’s surface.
Uplift
The upward vertical motion of Earth’s surface.
Stress
The force acting on a surface.
Compression
Squeezing stress.
Tension
Stress that pulls plates apart.
Shear
Parallel forces acting in opposite directions.
Strain
A change in the shape of rock due to stress.
Elastic strain
Does not permanently change, or deform, rocks. It occurs when stresses are small or rocks are very strong.
Plastic strain
Creates a permanent change in shape.
Ocean Trenches
Deep, underwater troughs created by one plate subducting under another plate at a convergent plate boundary.
Volcanic Arc
The curved line of volcanic islands that forms parallel to a plate boundary.
Transform Faults
Form where tectonic plates slide horizontally past each other.
Fault Zone
An area of many fractured pieces of crust along a large fault.
Folded mountains
Are made of layers of rocks that are folded.
Fault-block mountains
Parallel ridges that form where blocks of crust move up at faults.
Uplifted Mountains
When large regions rise vertically with very little deformation.
Plain
An extensive area of level or rolling land.
Basins
Areas of subsidence and regions with low elevation.
