Unit 6 Part 2: Plate tectonics and Continental Drift

​Science Root of the Day:

DO NOW: Write what you think the example words mean in your lab manual.

Extra Credit: Find three additional words that use this root and write them and their definition in your lab manual (6 Points Max)

Plate Tectonics and Continental Drift

Multiple Choice

Temperature and pressure ___ as you move towards the center of the Earth.

• decrease

• increase

• Stay the same

Multiple Choice

The crust and upper portion of the mantle are called the

• asthenosphere.

• lithosphere.

Multiple Choice

Earth's magnetic field protects our atmosphere from...

• liquid metal layers

• North and south poles

• ocean floor striping

• solar winds and particles

Multiple Choice

Which layer is liquid?

• crust

• mantle

• outer core

• inner core

Lesson Objectives

• Describe Wegner's Theory of Continental Drift

• Explain how new lithosphere is created and old lithosphere is destroyed in seafloor spreading

• Summarize the Theory of plate tectonics

• Describe the role of mantle convection in tectonic plate motion

​What was Wegener's Hypothesis about continents?

• 1910: German Scientist Alfred Wegener observed the shapes of continents, and noted that several of them fit together like a puzzle

  • Wegener Hypothesized that at one point, they were together​ in one single landmass

    • Pangea: a super content that existed 300 million years ago

• Wegener proposed that the individual continents slowly moved apart due to continental drift

Match

Match the Numbers to the letters their landmass would connect to

• 1

• 2

• 3

• 4

B

A

D

C

• B

• A

• D

• C

​Evidence for Wegener's Hypothesis: Land

• Mountains on the continents of Africa and South America line up almost perfectly

• Coal fields in Europe and Nor​th America also line up

​Evidence for Wegener's Hypothesis: Fossils

• Glossopteris Plant fossils were found in Africa, South America, Australia, India, and Antarctica

  • There is no way for that plant to travel across oceans, so those landmasses must have been connected

• The reptiles Mesosaurus and Lystrosaurus were also found across continents

​Evidence for Wegener's Hypothesis: Climate

• As continents move towards the equator, they move to a warmer climate

• As they move toward the poles, the climate gets colder

• Fossils for animals and plants have been found in contents that currently, they could not live in.

  • Indicates the continent itself moved and carried the fossils with it

​Evidence for Wegener's Hypothesis

​Why Was Wegener's Hypothesis rejected?

• Wegener thought the continents moved while the oceans stayed put

  • Not quite correct​

• Could not​ prove his theory, so other geologists rejected it for several years

• Was first widely accepted after 1960​, when the ability to study movements of continents was made easier by modern technology

Multiple Choice

How would the climate of a continent change if it drifted closer to the Equator?

• It would become Warmer

• It would become colder

• It wouldn't change at all

Multiple Choice

Deep scratches have been found in rocks in South Africa. These scratches could only have been caused by glaciers moving across the continent. Today the climate of South Africa, is too mild for glaciers to form, so we can infer that South Africa was once in a climate that was __________ than it is today.

• Warmer

• Colder

Multiple Choice

Based on evidence from land features, fossils, and climate, Wegener concluded that continents _________.

• Sink

• Rise

• Move

• Grow

Multiple Choice

Pangea is the Supercontinent that Wegener suggested occurred on Earth about 300 million years ago

• True

• False

Multiple Choice

Oceanic drift is the idea that the continents slowly moved over Earth's Surface

• True

• False

Multiple Choice

__________ of the plant Glossopteris provided evidence for Wegener's Hypothesis for the Continental drift.

• Species

• Seeds

• Fossils

• Samples

​What are Mid-Ocean Ridges?

• In different areas of the Ocean floor, the floor showed signs of "seams" like those on a baseball

  • Curve along the the ocean floor

  • Form Mountain ranges

• Mid-ocean Ridges: long chains of mountains that rise up from the ocean floor​

How do we Study Mid-Ocean Ridges?

• In the 1990s, scientists used Sonar to map the ridges

  • Sonar uses sound waves to measure the distance to an object

  • Showed them to be the longest mountain range on Earth

Where are Mid-Ocean Ridges?

• Maps showed the ridges extend into all oceans

  • Under thousands of meters of water

  • ​The mid-ocean ridges are split by a steep valley

​What is Sea-Floor Spreading?

• By the 1960s, geologists had begun to learn more about mid-ocean ridges

• Mid-ocean ridges add new material to the ocean floor

• Sea Floor Spreading: the process by which new material is added to the ocean floor by mid-ocean ridges​

  • A mid-ocean ridge forms in the oceanic crust

  • Magma: Molten material from the Earth's Interior

    • rises through cracks in the crust cools, and hardens

  • Over time, the strips of rock move outward from the ridge

​Evidence for Sea-Floor Spreading: Ocean Material

• In the central ridges, scientists found rocks shaped like pillows

  • This only happens when molten material hardens quickly

​Evidence for Sea-Floor Spreading: Magnetic Strips

• As molten material cools and hardens, magnetic material in it aligns with the direction of Earth's poles​ at times of eruption

  • Poles can reverse direction, so the magnetic stripes can indicate when molten material erupted

• Magnetic stripes are mirror images on either side of the ridge

​Evidence for Sea-Floor Spreading: Drilling Samples

• Rock Samples drilled up from the Ocean crust allowed scientists to compare the ages of samples from different locations

  • The farther from the ridge a sample was taken from, the older the rock

Grade 8 Ohio | Lesion 5.4

Multiple Choice

In Sea-floor spreading, new crust is added at a

• Magnetic Stripe

• Hot Spot

• Mid-ocean ridge

• Lava location

Multiple Choice

Which of the following is not evidence of sea floor spreading?

• Drilling Samples

• Magnetic Stripes

• Animal life on the Ocean Floor

• Hardened Ocean Material

​What Happens at Deep-Ocean Trenches?

• The ocean floor does not continue to get wider without stopping

  • Eventually, the ocean floor plunges into underwater canyons

• ​Deep-ocean trenches: deep underwater canyons where the oceanic crust bends downwards

  • The sinking into the mantle of crust takes tens of millions of years​

​The Process of Subduction

• Subduction: The process by which the ocean floor sinks beneath a deep ocean trench back into the mantle

• As new material on the ocean floor is created and cooled, it's density changes

  • Initially has a low density when hot, and the density increases as it cools

• While new material cools, it can collide with continental crust

  • Older crust is then pushed down towards the mantle​

​Subduction and Earth's Ocean

• Subduction and sea-floor spreading work together to change the size and shape of the ocean

  • They work together like a conveyor belt, replacing the ocean floor every 200 million years

• Size of the crust is determined by how fast crust is being created and destroyed in subduction

Multiple Choice

In seafloor spreading, molten material rises from the mantle and erupts

• along the edges of all the continents.

• along mid-ocean ridges

• in deep-ocean trenches

• at the north and south poles

Multiple Choice

Old oceanic crust is more dense than new oceanic crust because it is

• Hotter

• Cooler

• Taller

• Shorter

Multiple Choice

___________ is a device that scientists use to map the ocean floor.

• Sonar

• Conduction

• Crust

• Fossil

​Convection

• Heat transfer by the movement of a fluid

  • a fluid can be a gas or a liquid

  • convection creates currents​

​How does Convection Occur in Earth's Mantle

• The mantle and core of the Earth are extremely hot

  • Heat inside the Earth originated​ from gravitational energy and decay of radioactive elements

• Heat transfers from the mantle and core in different ways

​Convection Currents

• Density: A measure of how much mass is in a given volume of a substance​

  • As objects warm and expand, they become less dense

• When a liquid heats, the liquid at the bottom warms and expands quickly

  • As the density of the liquid decreases, the liquid begins to rise and float over the cooler liquid

    • The liquid that rises eventually cools and sinks below the warming liquid, creating a cycle

• Convection Currents: Flows that transfer heat within a fluid

  • If the heat disappears, the current stops

​Convection Currents

​Convection Currents in the Earth

• The Core of the Earth acts as a heat source

• Heat from the innercore drives convection currents throughout the outer core, mantle, and crust​

  • The mantle is a semisolid material that flows​

Multiple Choice

What does a convection current transfer within a fluid?

• heat

• air

• water

• smoke

Multiple Select

What would happen to convection currents if the inner Earth Cooled down

• They would continue at the same speed

• They would move faster

• They would move slower

• They would stop