Geologic Processes within the Earth (Seafloor Spreading)
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The ocean floor, previously believed to be flat, has turned out to be more fascinating than we once thought. Thanks to technologies like sonar and magnetic studies, we've discovered a dynamic underwater world with mountains and canyons. As we delve into the secrets of the ocean floor, we come across evidence that challenges our earlier, simpler understanding.
Objectives
Objectives
discuss the process of seafloor spreading; and
explain how the convection currents in the earth’s interior make the seafloor spread.
describe the three evidence that seafloor is continuously spreading.
Content
Content
Magnetic Stripes and Seafloor Features
Mapping the Seafloor Terrain
Magnetic Polarity Patterns:
Normal and reversed magnetic patterns along the seafloor.
Creation of magnetic stripes, uncovering distinct features like continental shelf, slope, abyssal plain, mid-ocean ridge, seamount, and trench.
Seafloor Spreading Mechanism
The Engine Behind Seafloor Transformation
Explanation by Harry Hess:
Convection currents in the Earth's interior drive seafloor spreading.
Magma movement from the mantle forms new crust at mid-ocean ridges.
Older crust is pushed aside, creating a continuous recycling process.
Age Discrepancy in Seafloor
Comparison of Seafloor and Land Rocks:
Oldest seafloor (180 million years) younger than oldest land rocks (3 billion years).
Demonstrates the dynamic and evolving nature of the ocean floor.
Evidence for Continuous Seafloor Spreading
1. Molten Materials:
Pillow-shaped rocks indicate repeated eruptions from mid-ocean ridge cracks.
2. Magnetic Strips:
Magnetized rock stripes record magnetic field reversals.
3. Drilling Samples:
Core samples reveal older rocks farther from the ridge, showcasing the ongoing process of seafloor spreading.
Innovative Lab Activity:Â Seafloor Spreading
Objective: To create a hands-on, innovative laboratory activity that simulates seafloor spreading, providing a dynamic and easy-to-understand exploration of geological processes.
Materials:
Shallow Plastic Tub: Represents the ocean floor.
Modeling Clay (Two Colors): Easy-to-mold clay for creating the seafloor and mid-ocean ridge.
Table Lamp or Desk Lamp: Simulates the heat source representing Earth's interior heat.
Flat Plastic Spatula or Spoon: Represents tectonic movement and helps demonstrate seafloor spreading.
Water Spray Bottle: Cools and solidifies the "newly formed crust."
Ruler or Measuring Tape: Measures the distance of the "new crust" from the mid-ocean ridge.
Procedure:
1.Ocean Floor Setup:
Place the shallow plastic tub on a flat surface.
Use one color of modeling clay to create a flat ocean floor inside the tub.
2.Mid-Ocean Ridge Construction:
Build a raised mid-ocean ridge along the center of the tub using the second color of modeling clay.
3.Convection Current Simulation:
Position the lamp above the tub to act as a heat source, symbolizing convection currents.
Observe and discuss how the heat causes the clay at the mid-ocean ridge to rise.
4.Seafloor Spreading Demonstration:
Show how the rising clay spreads on both sides of the ridge, representing seafloor spreading.
Use the spatula to illustrate the pushing aside of older crust as new crust forms.
5.Cooling and Solidifying:
Spritz water on the newly formed clay to cool and solidify it as it moves away from the ridge.
6.Measurement and Analysis:
Measure the distance between the ridge and the edges of the "newly formed crust" using the ruler or measuring tape.
Discuss the concept of age-distance relationship, emphasizing the younger crust near the ridge.
Guide Questions:
1.What are we representing with the plastic tub in our simulation?
2.Why did we use a lamp in our activity?
3.What does the spatula represent in our simulation?
Evaluation
Evaluation
Direction: Choose the best correct answer and write it before the number.
1.What technology helped unveil the complex features of the ocean floor?
A) Radar
B) Sonar
C) Lidar
D) Satellite Imaging
Answer: B) Sonar
2.How did scientists discover the magnetic properties of the seafloor during World War II?
A) Magnetometers
B) Radiowaves
C) Telescopes
D) Microscopes
Answer: A) Magnetometers
3.What geological features are mapped by magnetic polarity patterns on the seafloor?
A) Deserts
B) Mountains
C) Mid-ocean ridges, trenches, and more
D) Glaciers
Answer: C) Mid-ocean ridges, trenches, and more
4.Who explained the role of convection currents in making the seafloor spread?
A) Isaac Newton
B) Marie Curie
C) Harry Hess
D) Charles Darwin
Answer: C) Harry Hess
5.Why is the oldest seafloor younger than the oldest land rocks?
A) Due to erosion
B) Tectonic activity
C) Seafloor spreading
D) Meteorite impacts
Answer: C) Seafloor spreading
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