PLATE TECTONICS

The North American plate and the Eurasian plate are moving _______ ___ __ _____ ___ ______ __.__ ____________ ____ _____.

Apart at a rate of about 2.5 centimeters per year

How does the concept of sea-floor spreading help support the idea that continents drift (thereby supporting Wegener's theory)?

As magma is thrust up and hardens forming new crust , the ocean floor on both sides of the mid -ocean ridge move outward carrying the continents along with them.

Where does sea-floor spreading began?

At the mid-ocean ridge

dMostdivergent boundaries occur along ____ ______ _______ where ____ ______ __________ occurs

Mid ocean ridges and sea floor spreading

The ocean floor has mountain chains that are as impressive as those on land. What are these underwater mountain chains called?

Mid- ocean ridges

Where do mid-ocean ridges form?

Mid- ocean ridges form along divergent boundaries (where two plates are pulling away from another) and every part of the worlds ocean.

What type of landforms are created when two ocean plates diverge?

Mid-ocean ridges, mountain ranges, central valley (new crust is formed)

What happens when two plates carrying continental crust collide? Does one subduct? Why or why not

No, since both sides generally have the same density neither is dense enough to sink very far into the mantle.

Why is the Atlantic ocean expanding?

The Atlantic has fewer deep-ocean trenches so more crust is subducted(destroyed) in the trenches

What happens to the density and temperature of oceanic crust as it spreads away from the mid ocean ridge?

The density increases and the temperature decreases

Why country of Iceland unique?

The mountains of the mid-ocean ridge rarely are found above the surface of the ocean, but such is the case in Iceland. A part of the mid-Atlantic ridge rises above the surface in the North Atlantic Ocean and forms the country of Iceland.

When oceanic crust collides with continental crust what happens?explain why it happens.

The oceanic crust will subduct the continental crust because it is more dense

What is the theory of plate tectonics?

The theory of plate tectonics states that the Earth's tectonics plates are constantly moving in slow motion

What type of landforms are created when two oceanic plates converge?

Trench

How do mid ocean ridges form?

Underneath the ocean, deep in the earth convection currents bring molten material up to the upper mantle. This material rises through faults (cracks) between oceanic plates that are moving away from one another. This material fills the cracks, hardens,and forms new crust. This process repeats many times and eventually forms an underwater mountain range.

According to Wegener how do mts form?

Wegener believed mts formed when continents collided, causing the edges of the continents to crumble and fold pushing up into huge mts.

Why was Wegener's hypothesis rejected by most of the geologist of his day?

Wegener could not explain the forces that are powerful enough to push or pull continents.

Who was Alfred Wegener and what was his hypothesis concerning earths continents?

Wegener was a German scientist who hypothesized that the earths continents were once all joined together in a single landmass and have since drifted apart

What happens to the rock (oceanic crust) along the mid-ocean ridges when new crust is formed?

When new crust is formed along the mid-ocean ridge, the old rock/crust is pushed out way from the ridge. So, the further away you get from the ridge , the older the rock/crust gets.

When two plates collide, what determines which one comes out on top?

When two plates collide the density of the plates determines which one comes out on top. The one with the greater density will subduct the less dense plate.

Is sea-floor spreading occurring today? Give an explanation for your answer.

Yes, sea-floor spreading continues today. We know this for several reasons:1)current GPS, satellite, and computer technology allow us to tell the exact position/location of all of Earth's landforms to within mm; and we have evidence of sea-floor spreading in the seismic activity (earthquakes and tremors) that occur around the world all of the time.

Based on your understanding of Pangaea will there ever be another supercontinent? Support your opinion which logical reasoning.

Yes, there will likely be another supercontinent. We know that the continents continue to move because of new technologies that allow us to track their movement, because we know the seafloor continues to spread (which means the continents are being moved along with the crust),and because there continue to be earthquakes and volcanic activity.

What event often occurs along transform boundaries?

earthquakes

Is crust created or destroyed at a transform boundary?

neither created or destroyed

What force is acting on the oceanic crust to pull it down beneath the trench?

Gravity

What "radical idea"did Hess propose?

He proposed that a process he called sea-floor spreading was continually adding new material to the ocean floor

Who was Harry Hess and what did he study?

He was an American geologist who studied mid ocean ridges

What happens to oceanic crust at deep-ocean trenches?

It eventually sinks back into the mantle

Earth's lithosphere , it's solid outer shell, is broken into separate sections called

Tectonic plates

Plate movement is measured by instruments minted onto satellites that orbit the earth. The plates move at a rate of __ to ____ _____________ per year.

1 to 24 centimeters

What evidence did Wegener gather and study to support his hypothesis?

1) he studied land features. Wegener examining land features such as the margins of the continents, mountain belts,rock layers, and mineral deposits and matched these features with similar features found on other continents. 2) he examined the fossil record. Wegener identified the remains of identical plants and animal fossils on separate continents. 3) he study climate change along with the fossil record and made the case for the movement of landmasses towards and away from the equator and the poles over millions of years. (To explain things like finding the fossils of warm water see creatures and tropical plants in the polar regions.)

Alfred Wagner, a Canadian scientist developed the theory of plate tectonics based on what three observations ?

1) that there were cracks in the continents similar to the cracks found on the ocean floor 2)sea-floor spreading 3)continental drift

Every ____ __________ years do you lock forms at the mid Ocean Ridge, move it across the ocean, and sync it to a stretch...recycling itself

200 million

What is a rift valley? Where can a good example be found?

A Rift Valley is formed when a divergent boundary develops on land(the earths plates in that area move apart) and a deep Valley forms. One of the most well known examples of a rift valley can be found in East Africa.

What do we call it when two plates converge?

A collision

What is a deep-ocean trench and how does it form?

A deep ocean trench is an underwater canyon that forms when older, more dense oceanic crust begins to bend downward (sub ducts)

Where are transform boundaries?

Between part of the North American and pacific plates (Northern California)

Where are convergent boundaries?

Between the Eurasian and Pacific plates and the Eurasian and Indo- Australia plates

Where are divergent boundaries?

Between the North American and Eurasian plates and South American and African plates

Compare is the thickness and density of continental crust to oceanic crust

Continental crust is thicker but oceanic crust is more dense

What was the name given to wegeners theory that continents slowly move over the earths surface?

Continental drift

What force do geologists believe is responsible for the movement of the continents?

Convection currents in the mantle

Plates at different types of boundaries move ___________.

Differently

What name was given to this single landmass or supercontinent?

Pangea

When did Pangea form?

Pangea formed about 3 million years ago

What is the name given to an area where tectonic plates meet?

Plate boundary

How do tectonic plates move at the convergent boundary?

Plates come together or move toward each other

How do tectonic plates move at the divergent boundary?

Plates move apart or away from each other in opposite directions

How do tectonic plates move at the transform boundary?

Plates slide past one another going in opposite directions (like rubbing hands together)

What type of lamp arms are created when two continental plates diverge?

Rift valley, volcanoes

What evidence did scientists discover to support the theory of sea-floor spreading when they examined rock samples taken from the sea floor by the drilling ship, Glomar Challenger?

Rock samples from different areas of the sea floor were brought up through pipes and then scientists determined the age of each rock sample. They discovered that the oldest rock/crust was farthest away from the mid-ocean ridge and that was the youngest rock/crust was on the mid-ocean ridge.

Explain the process of sea-floor spreading

Seafloor spreading occurs when the seafloor spreads apart along divergent boundaries and forms the mid-ocean ridge. Magma is pushed up through the crust along the mid ocean ridge. As the magma is the thrust up and hardens it forms new crust and the ocean floor on both sides of the mid- ocean ridge move outward.

The processes of seafloor spreading and subduction can change the _______ and __________ of oceans

Size and shape

How did scientists determine the location and size of these underwater mountain chains?

Sonar

What technology/technologies existed during Hess's lifetime that did not exist during Wegener's that allowed Hess to prove the theory of sea-floor spreading?

Sonar,submersibles (submarines), tools for deeper oceanic drilling

What is this process called?

Subduction

The Pacific ocean covers approximately 30% of the earths surface, but is it shrinking. Why?

Subduction in the many deep-ocean trenches is occurring faster than new crust is being added ( more crust is sinking back into the mantle at the deep-ocean trenches than is being created along the mid-ocean).

What type of landforms are created when an oceanic and a continental plates converge?

Subduction zone, volcanic islands, trenches crust is destroyed