Plate Tectonics

Plate Tectonics

Multiple Choice Practice

Multiple Choice

A statement that’s accuracy can be tested by experiments and through observations is formally called a _______________.

• proposition

• conclusion

• hypothesis

• deduction

Wegener's Hypothesis

• Geologist Alfred Wegener noticed similar rocks & fossil remains were found on continents which seemed to fit together

• He called this “super” continent called Pangaea

• continental drift: the hypothesis that the continents slowly drifted to their current positions after having been part of a single, giant landmass that broke apart]

Pangaea: The Supercontinent

Wegener thought that the continents were once a single landmass, which he called Pangaea. He proposed that this supercontinent split into separate continents that slowly “drifted” to their current positions. Note that scientists refer to Europe and Asia as one continent. They also think that India was a single continent for a time after Pangaea broke up.

Multiple Choice

Lana knows Wegener’s hypothesis: that the continents had once been a part of a single land mass, and that the continents had slowly drifted apart. And she knows some of the evidence that supports the hypothesis.

What evidence does the map provide that Lana can use to support the continental drift hypothesis?

• The continents fit well together.

• Several continents have similar rock formations.

• Similar plant fossils are found on several continents.

• Similar mountain ranges are located on several continents.

Multiple Choice

The process of _________ occurs when large landmasses move, like when Pangea broke apart.

• plate shift

• continental drift

• land transference

• landmass movement

Multiple Choice

How did the Appalachian Mountains in North America and the Atlas Mountains in North Africa provide evidence for Pangea?

• Neither range contained fossils prevalent near the equator.

• Both ranges are comprised of a diverse assortment of rock types.

• Both ranges had similar types, ages, and sequences of rock layers, suggesting that they were formed together and then separated.

Discovering Earth’s Interior

- Earthquakes cause vibrations called seismic waves, which travel through Earth’s interior.

- A seismograph, records these vibrations for scientists to analyze

-The structure of Earth’s interior is determined by measuring seismic waves.

-Scientists discovered that the crust beneath the oceans, called oceanic crust, is thinner than continental crust

• Seismic waves have two properties that helped reveal the nature of Earth’s interior.

• 1. seismic waves travel faster through denser rock than through less dense rock.

• 2.Seismic waves change direction slightly as they pass through rocks of different densities.

• The crust and the rigid outer layer of the mantle form what’s called the lithosphere.

Multiple Choice

The crust beneath oceans, _________ crust, is thinner than the crust beneath continents, __________crust.

• water; land

• aquatic; rocky

• oceanic; continental

• marine; terrestrial

Multiple Choice

Which of the following statements is NOT true of seismic waves?

• Seismic waves are vibrations that result from earthquakes.

• Studying seismic waves helps scientists study the Earth’s interior.

• Seismic waves travel at the same speed regardless of rock density.

• As they pass through rocks of different densities seismic waves change direction slightly.

Observing Patterns of Volcanoes and Earthquakes

Most of the world’s volcanoes and earthquakes are located along the edges of continents and ocean basins and along island chains. The Pacific Ring of Fire is the most concentrated zone of volcanic and earthquake activity on Earth.

Multiple Choice

What is the pattern of earthquakes and volcanoes across the Earth?

• They are both mostly found in narrow zones around the edges of continents and ocean basins and along island chains.

• Earthquakes occur wherever volcanoes do not.

• They are both spread evenly across the Earth.

Discovering Features of the Seafloor

• To study the seafloor, scientists used a technology called sonar (sound navigation and ranging).

• Scientists observed that: 1) the ocean floor had mountain ranges and deep trenches. 2) rock closer to mid-ocean ridges is younger than rock further away from mid-ocean ridges, and rock in continental plates is older than rock in oceanic plates. 3) The mountains on either side of the cracks move past each other in opposite directions. Scientists call these features fracture zones (a kind of fault)

• The biggest is a chain of volcanic mountains called the mid-ocean ridge.

• As oceanic crust moves away from the mid-ocean ridge, it cools and becomes denser.

Seafloor Spreading

• seafloor spreading: the process by which the rocks on either side of the mid-ocean ridge slowly pull away from each other, allowing molten rock to rise, solidify, and form new seafloor

• The youngest rocks (in red) occur along the mid-ocean ridge.  The oldest rocks (in blue) occur farthest away from the mid-ocean ridge.

Multiple Choice

A chain of volcanic mountains found on the seafloor is called a __________.

• trench

• mid ocean ridge

• fracture zone

Multiple Choice

Scientists have found that rocks closer to the mid-ocean ridge are less dense than those further away. Which statement would explain these findings?

• Rocks closer to the mid-ocean ridge are under greater tectonic pressure and are denser than rocks further from the ridge.

• Rocks closer to the mid-ocean ridge are made of rocks with different, denser minerals than rocks further from the ridge.

• Rocks near the mid-ocean ridge are closer to volcanic activity and are warmer; warmer rocks are less dense than cooler rocks.

• Rocks near the mid-ocean ridge are further from volcanic activity and are cooler; cooler rocks are less dense than warmer rocks.

Multiple Choice

Rocks near mid-ocean ridges are _________ rocks further away. This phenomenon is due to a process called __________.

• the same age as; weathering

• younger than; seafloor spreading

• a different type from; deposition

The theory of plate tectonics describes how the lithosphere is made of rigid plates that move slowly across Earth’s surface. There are 15 major tectonic plates, shown here, along with several smaller plates.

Plate tectonics 

• Plate tectonics is the theory that the lithosphere is made up of tectonic plates, that move across Earth’s surface.

• Convection in the mantle is one of the main causes of tectonic plate motion. 

•  Because of seafloor spreading, the new rock moves farther and farther away from the mid-ocean ridge. As it does so, it becomes cooler and denser, and eventually sinks down at trenches.

•  As the hot rock rises under the mid-ocean ridge, it melts and becomes magma. This magma erupts along cracks between the two tectonic plates.

• Mantle convection, seafloor spreading, and subduction provide the missing mechanisms that Wegener was searching for to explain how continents move.

Tracking Plate Motion

• A convergent boundary occurs where two plates move toward each other. The movement of two plates towards each other is called convergent motion.

•  A divergent boundary occurs where two plates move away from each other. The movement of two plates away from each other is called divergent motion.

• A transform boundary occurs where two plates slide past each other. The sideways motion of the plates, called transform motion, does not happen smoothly. 

Tracking Plate Motion

• Convergent motion causes a trench to form on the seafloor, and part of the subducting plate melts to form pockets of magma. The magma rises toward the surface and results in volcanoes.

• Divergent motion causes causes oceans and seas to become wider (seafloor spreading)

• Transform motion causes earthquakes

Multiple Choice

The theory of plate tectonics says that rigid pieces of the lithosphere, called _________, move across the Earth’s surface very slowly.

• landmasses

• tectonic plates

• Wegener's pieces

Multiple Choice

A trench forms at what kind of plate boundary?

• convergent

• divergent

• transform

Multiple Choice

Felix is interested in the way the South American Plate moves in relation to the plates that it touches. Based on evidence from the map, which statements should Felix make to BEST describe the interactions of this tectonic plate?

• The South American Plate diverges from both the African Plate and the Nazca Plate

• The South American Plate converges with both the African Plate and the Nazca Plate

• The South American Plate diverges from the African Plate and converges with the Nazca Plate

Multiple Choice

Plate boundaries that have convergent motion, such as the one between the Australian and Pacific Plates, are sometimes called “destructive margins”. What statement below BEST explains why this boundary is “destructive”?

• As one plate subducts under the other, the plate that subducts melts into magma.

• As one plate moves away from the other, the crust spreads and new crust upwells.

• As these plates slide past each other, they create a transform fault where some of the material erodes away