1. What does the ocean floor look like? Directions: Teacher reads opening section, then students are given print outs of slides (1- 6) that include the remaining 6 parts. Have the students read their part while the rest of the group listens and looks at the numbered features on their included ocean floor map. After #6 is read, the teacher closes the activity by reading the last section. We can all imagine a walk across North America: crossing the Mississippi, traversing the Great Plains, scaling the Rockies. But what would it be like to walk from New York Harbor to the coast of Great Britain? Would the land above water resemble the land beneath it? What does the ocean floor look like? You might be surprised. Below the surface of the ocean’s great blue expanse is a terrain more varied and dramatic than any landmass on earth: mountains taller than Everest, chasms deeper than the Grand Canyon, and plains more expansive than the Siberian steppes. A walk across the ocean floor

2. 1 2 3 4 5 6 #1 Our journey begins with a shallow descent from a mid-Atlantic beach to the continental shelf, a narrow ribbon of seafloor that extends around the world’s continents and ranges between 30 and 1300 km wide. At the edge it’s only about 200m deep. A uniform layer of mud and other sediments that originated on land covers most of the continental shelf. Most fish are caught in its teeming waters, which are also home to the bulk of the oceans’ vegetation and animal life. The edge of the shelf is the sea that most of us are familiar with, where we swim, fish, and go boating; it’s relatively warm and shallow.

3. 1 2 3 4 5 6 #2 Next we reach the continental slope, where the sea floor begins its descent to the depths. Typical slopes have an incline of 4 degrees, although they can be as steep as 25 degrees. Cutting through parts of the slope are immense V-shaped canyons that wind outward to the deep sea and often connect to the mouths of rivers. (When sediment that has accumulated on the shelf becomes unstable or is shaken by earthquakes, it can avalanche down these canyons. This can trigger tsunamis.

4. 1 2 3 4 5 6 #3 The continental rise, at the base of the continental slope, is where sediments have descended from the continental shelf and accumulated. The width of the rise can vary from 100 to 1,000 km, and it has a very gradual slope. Now that we’ve hit the deep ocean basin, we can set out on the long trek across the ocean floor.

5. 1 2 3 4 5 6 #4 All the way down at depths below about 4,000 m (2.5 mi), the seafloor is called the abyssal plain. It is essentially flat because the rugged topography of the underlying basaltic crust is draped in sediment that can be up to five km (three mi) thick. The abyssal plains cover 25% of the Earth’s surface. Great expanses appear barren, but in fact the animals that live on the seafloor — called benthos — are abundant and diverse. Most are invertebrates (such as sea anemones, sponges, corals, sea stars, sea urchins, worms, bivalves, and crabs) that have adapted to the cold water and high pressure with slow metabolisms.

6. 1 2 3 4 5 6 #5 Near the center of the ocean basin we find ourselves climbing a mid- ocean ridge: a line of volcanoes about 1.2 miles high and 43,000 miles long that stretches across the ocean floor and around the Earth like the seams on a baseball. Also called spreading centers, these mid-ocean ridges are where new oceanic crust is created. Luckily, we’re not in the Pacific Ocean, where we’d have to hurdle an ocean trench or two. Trenches are two to three miles deeper than the adjacent ocean floor, these are the deepest places on the Earth’s surface. The most famous one is the Mariana Trench of the western Pacific. It’s over 7 miles deep — way deeper than Mt. Everest is high — and about 1,584 miles long and 43 miles wide.

7. 1 2 3 4 5 6 #6 And along our journey, we’re bound to hit seamounts and guyots, small, circular, steep-sided volcanic structures about one kilometer high, which do not rise above sea level. They can be found in groups of up to 100, or by themselves. Most are inactive volcanoes that formed at mid-ocean ridges, though some are thought to result from hot-spot volcanism. These spots stay stationary while the rocky plates that make up the Earth’s surface move across them. The result is chains of volcanoes like those that make up the Hawaiian Islands. After a 4,000 mile trek across the Atlantic Ocean basin, we begin climbing up the continental margin to dry off on the west coast of Ireland.

8. Back to the land So what does the ocean floor look like? A vast expanse of seemingly barren desert, punctuated by some of the most intense geologic features and activity on the planet — hardly the homogenous place suggested by those miles and miles of unbroken blue. Exploring the ocean was once limited to what could be seen from shore or a ship or by diving down a few meters. Today, small submarines have become invaluable research vessels for scientists. These and other new tools — satellites, robotic vehicles and self-propelled, datalogging buoys — are helping us discover new species, uncover new resources, and understand how interconnected the oceans are with the rest of the planet. Still, less than 5% of the deep ocean has been explored. Imagine the possibilities.