Sea Floor Spreading: A diagram illustrating the age of ocean floor rocks, demonstrating sea floor spreading from the Mid-Atlantic Ridge.

Problem Overview:

The task involves analyzing a map of the North Atlantic Ocean floor to understand how the age of rocks provides evidence for sea-floor spreading. The steps include identifying key regions, shading rock ages, measuring distances, calculating actual distances, graphing data, and answering questions about the relationship between rock age and distance from the Mid-Atlantic Ridge.

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Solution Explanation:

#### Step 1: Locate Key Regions and Trace the Mid-Atlantic Ridge
1. Identify the United States, Africa, and Europe on the map.
- These are labeled on the map.
2. Shade these regions with a brown colored pencil.
- This step helps focus attention on the areas of interest.
3. Locate and trace the dashed line in the middle of the map.
- This dashed line represents the Mid-Atlantic Ridge, which is the boundary where new oceanic crust forms due to sea-floor spreading.

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#### Step 2: Shade the Age Bands
1. Use the provided color coding to shade the different age bands on the map:
- Mid-Atlantic Ridge (0–63 million years): Leave white.
- 63–91 million years: Yellow.
- 91–135 million years: Green.
- 135–180 million years: Orange.
- Older than 180 million years: Purple.

- Reasoning: Shading by age helps visualize how rock ages increase as you move away from the Mid-Atlantic Ridge, providing evidence for sea-floor spreading.

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#### Step 3: Measure Distances from the Mid-Atlantic Ridge
1. Use a ruler to measure the distance (in centimeters) from the Mid-Atlantic Ridge to each dot on the map.
2. Record these measurements in Column B of the data chart.

- Example Measurement:
- If a dot is 2.5 cm from the ridge, record "2.5" in Column B.

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#### Step 4: Calculate Actual Distances
1. Convert the measured distances (in cm) to actual distances (in km) using the scale:
- Scale: 1 cm = 700 km.
- Multiply the values in Column B by 700 to get the actual distances in kilometers.
- Record these values in Column C.

- Example Calculation:
- If a measurement is 2.5 cm, then \( 2.5 \times 700 = 1750 \) km.
- Record "1750" in Column C.

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#### Step 5: Graph the Data
1. Create a graph with:
- X-axis: "Age of Sea Floor (millions of years)" (Column A).
- Y-axis: "Distance from Mid-Atlantic Ridge (km)" (Column C).
- Label each axis appropriately.
- Plot the data points from the chart and connect them to form a line graph.

- Reasoning: The graph will show a linear relationship between rock age and distance from the ridge, indicating that older rocks are farther away, consistent with sea-floor spreading.

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#### Step 6: Answer the Questions
1. This graph represents the relationship between ______ and ______ from the Mid-Atlantic Ridge.
- Answer: This graph represents the relationship between age of the sea floor and distance from the Mid-Atlantic Ridge.

2. What does this information tell us about the age of rock as it gets further away from the mid-ocean ridge?
- Answer: As the distance from the Mid-Atlantic Ridge increases, the age of the rock also increases. This is because new crust forms at the ridge and moves outward over time due to sea-floor spreading.

3. What do you notice about the banding on both sides of the Mid-Atlantic Ridge? How does this provide evidence for sea-floor spreading?
- Observation: The banding shows symmetrical patterns of rock ages on either side of the ridge. Rocks closest to the ridge are youngest, and their age increases symmetrically as you move away from the ridge.
- Evidence for Sea-Floor Spreading: This symmetry indicates that new crust is forming at the ridge and moving outward in both directions. The matching ages on either side confirm that the process is uniform and ongoing.

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Final Answer:

\[
\boxed{
\text{1. Age of the sea floor and distance.}
\text{2. Rock age increases as it gets farther away from the ridge.}
\text{3. Symmetrical banding shows matching ages on both sides, confirming sea-floor spreading.}
}
\]