Transcript What does the ocean floor look likex

What does the ocean floor look like?
Directions: Teacher reads opening section, then students are given print outs of slides (16) 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
#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.
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#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.
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#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.
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#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.
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#5
Near the center of the ocean basin
we find ourselves climbing a midocean 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.
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#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.
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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.