CHAPTER 4: PLATE TECTONICSLESSON 1: CONTINENTAL DRIFT QUIZ G

1. Wegener proposed the continental drift hypothesis suggesting that continents are in constant motion on the surface of the Earth.2. Glossopteris was a supercontinent consisting of Earth’s present-day continents.3. One of Alfred Wegener’s pieces of evidence for continental drift was data from the seafloor.4. Wegener used fossils to suggest that a supercontinent existed about 250 million years ago.

Label 1-8 on your paper. Write T or F for each.

CHAPTER 4: PLATE TECTONICSLESSON 1: CONTINENTAL DRIFT QUIZ G

5. Glacial grooves in rocks in Africa suggest that this continent was once located in a much colder place.6. Rocks with a similar makeup and age in South America and Africa supported Wegener’s idea of moving continents.7. Wegener’s hypothesis of moving continents was accepted by many because he had lots of data to support it.8. The puzzlelike fit of continental coastlines was one piece of evidence Wegener used to suggest that the continents were once joined.

CHAPTER 4: PLATE TECTONICSLESSON 1: CONTINENTAL DRIFT QUIZ A

1. State Alfred Wegener’s hypothesis of continental drift.

2. Explain how Wegener used the shapes of continents to support his hypothesisof continental drift.

3. Explain how Glossopteris fossils provide evidence of continental drift.

4. Identify two types of climate data used by Wegener to support his hypothesis.

5. Explain how Wegener used his studies of rocks to support continental drift.

6. Explain why Wegener’s hypothesis was not widely accepted by scientists at the time.

CHAPTER 4: PLATE TECTONICSLESSON 2: DEVELOPMENT OF A THEORY

Lesson 2 Vocabulary Words:

Mid-Ocean Ridge

Seafloor Spreading

Normal Polarity

Magnetic Reversal

Reversed Polarity

LESSON 2: DEVELOPMENT OF A THEORYMAPPING THE OCEAN FLOOR

• Using an echo sounder, scientists were able to determine the depth of the ocean and create a topographic map of it in the 1940’s.

• These maps revealed vast mountain ranges that stretched for miles on the ocean floor.

• Mid-ocean ridges are mountain ranges in the middle of the oceans, and are much longer than mountains on land.

LESSON 2: DEVELOPMENT OF A THEORYSEAFLOOR SPREADING

• By the 1960’s, scientists discovered a new process that helped explain continental drift.

• 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.

• When the seafloor spreads, the mantle below melts and forms magma.

• Magma erupts on Earth’s surface as lava, and crystallizes on the seafloor, forming Basalt.

LESSON 2: DEVELOPMENT OF A THEORYSEAFLOOR SPREADING

•Because the lava erupts under water, it cools rapidly and forms rounded structures called pillow lava.

•As the seafloor continues to spread, the older oceanic crust moves away from the mid-ocean ridge.

LESSON 2: DEVELOPMENT OF A THEORYSEAFLOOR SPREADING

• The rugged mountains that make-up mid-ocean ridges form in two different ways:

1. Large amounts of lava can erupt from the center of the ridge, cool, and build-up around the ridge.

2. As the lava cools and forms new crust, it cracks and the rocks move up or down these cracks in the seafloor, forming jagged mountain ranges.

LESSON 2: DEVELOPMENT OF A THEORYSEAFLOOR SPREADING

• Over time, sediment accumulates in the ocean basins. Close to the mid-ocean ridge there is almost no sediment. Far from the mid-ocean ridge, the layer of sediment becomes thick enough to make the seafloor smooth.

• The smooth part of the seafloor is called the abyssal plain.

• Continents move as the seafloor spreads along a mid-ocean ridge.

LESSON 2: DEVELOPMENT OF A THEORYDEVELOPMENT OF A THEORY

• The first evidence used to support seafloor spreading was discovered by studying the magnetic signature of the rocks on the seafloor.

• Normal polarity is a state in which magnetized objects, such as compass needles, will orient themselves to point north. (Earth today)

• Sometimes a magnetic reversal occurs, and the magnetic field reverses directions.

LESSON 2: DEVELOPMENT OF A THEORYDEVELOPMENT OF A THEORY

• The opposite of normal polarity is reversed polarity- a state in which magnetized objects would reverse themselves and orient themselves to point south.

• Magnetic reversals occur naturally every few hundred thousand to few million years.

LESSON 2: DEVELOPMENT OF A THEORYDEVELOPMENT OF A THEORY

• Basalt on the seafloor contains iron-rich minerals that are magnetic.

• When magnetic minerals in cooling lava crystallize, they record the direction of Earth’s magnetic field at the time.

LESSON 2: DEVELOPMENT OF A THEORYDEVELOPMENT OF A THEORY

• Scientists studied magnetic minerals in rocks from the seafloor using a magnetometer to measure and record the magnetic signature of the rocks.

• They discovered parallel magnetic stripes on either side of the mid-ocean ridge.

• Each pair of stripes had 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.

LESSON 2: DEVELOPMENT OF A THEORYDEVELOPMENT OF A THEORY

• Other measurements made on the seafloor also confirm seafloor spreading.

• Measurements have confirmed that more thermal energy leaves Earth near mid-ocean ridges than is released from beneath 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.

USING PG. 122, LABEL THE DIAGRAM IN YOUR NOTES.

LESSON 2: DEVELOPMENT OF A THEORYMINI-LAB WARM-UP 15 MINUTES

Using the materials on your desk, start on number 4 on the worksheet with your group.

Make sure to complete number 5 and 6 in your notebook for today’s warm-up.

LESSON 2: DEVELOPMENT OF A THEORYLESSON REVIEW

Complete the lesson 2 review on page 126 in your

notebook.