Science Chapter 1/section 4 and 5 Flashcards
what is the mid ocean ridge
the longest chain of mountains in the world. It was mapped in the mid-1900s by scientists using sonar. It extends into all of the earth’s oceans and is mostly hidden underwater
what is sonar
a device that bounces sound waves off underwater objects and then records the echos of these sound waves. It maps the ocean floor
What happens to rock along the mid-ocean ridge when new molten material erupts
molten material rises from the mantle and erupts. The molten material then spreads out, pushing older rock to both sides of the ridge.
what is sea floor spreading
A term used by Harry Hess. It is when the molten material from the mantle erupts and pushes older rock to the side which causes new rock to form on the ocean floor.
What evidence support’s theory of sea floor spreading
evidence from molten material, evidence from magnetic stripes and evidence from drilling samples
what is the evidence from molten material that supports sea floor spreading
Using a submarine (called the Alvin) scientists saw rocks shaped like pillows that could only be formed when molten material hardens quickly after erupting underwater.
what evidence from magnetic stripes supports sea floor spreading
the rocks that makes up the ocean floor lie in patterns of magnetized stripes. They hold record of the reversals in the Earth’s magnetic field. The rocks contain iron which would line up with the magnetic pole. Some point north and some point south
what evidence from drilling supports sea floor spreading
Rock samples drilled into the ocean floor were brought up through pipes. The scientists found that the further away from the ridge the rock samples were taken- the older the rocks were. The youngest rocks were always in the center of the ridges.
How can the ocean floor keep getting wider
the ocean floor plunges into deep underwater canyons called deep ocean trenches. the trenches form where the oceanic crust bends downward.
what is subduction
the process by which the ocean floor sinks beneath a deep ocean trench and back into the mantle
Is new oceanic crust hot or cold
hot but as it moves away from the mid-ocean ridge, it cools and becomes more dense
How long does it take subduction to allow deep ocean trenches to sink back down into the mantle
tens of millions of years. the ocean floor is renewed every 200 million years
What is happening with subduction in the Pacific Ocean.
the mid-ocean ridge does not add new crust fast enough before it is swallowed by the deep ocean trenches- so the ocean floor is SHRINKING
What is happening with subduction in the Atlantic Ocean
the ocean floor is EXPANDING. The ocean floor has only a few short trenches so the spreading ocean floor has no where to go and the ocean floor is spreading which will cause the ocean to become wider
What is plate tectonics
A geological theory that states pieces of the Earth’s Lithosphere are in constant, slow motion, driven by convection currents.
What are plates
A section of the Lithosphere that slowly moves.
What are plate boundaries
The edges of different pieces of the Lithosphere
What are plate boundaries
They divide the lithosphere into large plates.
It is where the edges of different plates meet at lines.
What are faults
A break in Earth’s crust where rocks have slipped past each other- form along plate boundaries
What are convergent boundaries
Where two boundaries collide
What are divergent boundaries
A plate boundary where two plates move apart- or away from each other. They usually occur in the ocean ridge. They can occur on land- causing a deep valley (a rift valley)
What are convergent boundaries
Where two boundaries come together or converge- it is a collision. It can form a mountain range.
What are convergent boundaries
Where two boundaries come together or converge- it is a collision.
What are 3 types of plate boundaries
transform boundaries
divergent boundaries
convergent boundaries
What is the continents’ slow dance
The fact that the continents are moving slowly. They move about 1-10 cm per year.
When 2 plates collide, what determines which one comes out on top
The density of the plates- the less dense (or lighter) plate comes out on top
what does subduction mean
The process where oceanic crust sinks beneath a deep-ocean trench and back into the mantle at a convergent plate boundary
What happens when 2 plates carrying continental crust collide
subduction DOES NOT happen because both plates are low density.
What happens when 2 plates- one oceanic crust and one continental crust- collide
oceanic crust is more dense and goes under the continental crust- so the oceanic crust is subducted.
What major event in Earth’s history began about 225 million years ago? explain.
Pangea began to break apart and the continents began to form. Plate movements caused the land mass to split apart.
