Chapter 23.1 Studying the Ocean Floor

1. Chapter 23.1 Studying the Ocean Floor Place these answers onto your worksheets.

2. Studying the Ocean Floor • Echo sounding: Scientists track the amount of time it takes for a single or multiple beams of sonar to reach sea floor and echo back. • Sediment sampling: Scientists take core samplings of ocean sediment in order to study sediment layers. • Satellite observations: Satellites measure the time it takes a signal to bounce off ocean surface and determine ocean floor changes from differences in surface levels.

3. Section 23.2 The Continental Margin • Passive continental margin: Located away from plate boundaries, passive margins feature broad continental shelves and fairly gradual gradients across the continental slope and rise.

4. Section 23.2 The Continental Margin 2. Active continental margin: Located where continental and oceanic plates meet, active margins feature narrow continental shelves, precipitous continental slopes, and nearly nonexistent continental rises.

5. After You Read Describe how submarine canyons form. Underwater canyons either date back to rivers cut through the land in earlier times when sea levels were lower or form from the erosion effects of turbidity currents.

6. Section 23.3 The Ocean BasinsWhile You Read • Abyssal hill: Small rolling, sediment-covered hills formed as the sea-floor surface near mid-ocean ridges. • Abyssal plain: Flat area of sea floor created by sediment brought from continents by turbidity currents and then spread out by the sea.

7. Section 23.3 The Ocean BasinsWhile You Read 3. Deep-ocean trenches: Long, steep-sided troughs parallel to meeting of lithospheric plates, formed when one plate subducts beneath another. 4. Mid-ocean ridges: Undersea mountain ranges formed when lithospheric plates move apart, allowing magma to rise into the space and cool.

8. Section 23.3 The Ocean BasinsWhile You Read 5. Seamounts/guyots: Cone-shaped mountain peaks formed originally by volcanoes; when the sea erodes away the top, seamounts become guyots.

9. After You Read • Abyssal plain----------Atlantic ocean • Abyssal hills-------North Atlantic Ocean • Deep-ocean trenches----Indian Ocean, western Pacific Ocean; Java Trench, Manilla Trench, Philippine Trench d. Seamounts--------Hawaiian Islands

10. Section 23.4 Ocean Floor Sediments 1. Terrigenous sediments: bits and pieces of continents; carried by rivers or icebergs out to sea, particles range from gravel and sand to tiny grains and flakes, can travel great distance before settling to ocean floor.

11. Section 23.4 Ocean Floor Sediments 2. Hydrogenous sediments: chemical reactions cause minerals to crystallize from seawater, form very slowly on the sea floor in lumps; found in all oceans and in some lakes.

12. Section 23.4 Ocean Floor Sediments 3. Calcareous oozes: shells and skeletons of marine animals or plants; containing at least 30% calcium carbonate; dissolving into water as they fall; most common sediment found on half of sea floor.

13. Section 23.4 Ocean Floor Sediments 4. Siliceous oozes: skeletons of marine life containing silicon dioxide; most common near equator and around Antarctica.

14. Section 23.4 After You Read Why should we study ocean sediments? Ocean sediments contain information about Earth’s history. Sea creatures’ remains tell scientists about past changes in climate, water temperature, wind patterns, and glaciation. Understanding the past can help scientists predict and prepare for future changes.