!

Think about a spot in the ocean…..

• This is a place far far away… (Well far from sunlight anyway) Keeping that in mind…..

• What kinds of temperature would you expect?

• What kind of light?

Does this seem like a place where you might expect to find sea-life? • Did you say…

• You might be surprised.

• Some areas of the deep-ocean floor are brimming with life.

How does the water get warm enough to support life?• FIRST: Ocean water sinks through

cracks (vents) in the crust. (Remember the crust?)

• Second, the water is heated by coming into contact with the hot molten material in the mantle.

• Third, the water (now warm) is spurted back into the ocean! (This is called a hot water vent)

Here is one example…..

• This is a picture of a tube-worm.

• This bizzare creature lives in the “East Pacific Rise” – A region of the Pacific Ocean floor off the coasts of Mexico and South America!

do we study the Ocean Floor?

• The bottom of the ocean has some characteristics that make it hard to study.

• It’s….

• Because of this, Scientists had to develop a new technology to study it….

That device is…• Sonar is a super-cool device.

• Sonar sends out pulses of sounds that bounce off the ocean floor.

• The equipment then measures how quickly the sound waves return to the ship.

• It the bottom is close- the sound waves return FAST!!

• If the bottom is far- the sound waves return SLOW!

What SONAR discovered….

• What do you think the bottom of the ocean floor looks like?

• Before SONAR, people thought the ocean was flat (like West Texas)

• Instead, they discovered the Ocean was hiding deep canyons and mountain ranges!

Mid-Ocean Ridge

• Not only did they find that there were MOUNTAIN RANGES under the sea. They found that the longest mountain in the WHOLE WORLD was under the sea.

• This mountain range is called the

• One part of this mid-ocean ridge is the East Pacific Rise (Home to our bizarre tube-worms!)

How in the world did it get there?

• Now that they knew these mountains existed,

• Scientists wanted to know…

• did it get there?

• caused it?

One American Geologist who studied this was… Harry Hess

• In studying Ocean Floors, he discovered something previously thought IMPOSSIBLE! Maybe that Wegner guy was RIGHT!

• MAYBE The continents ARE moving!

• HE suggested something

• He proposed Ocean floors move like conveyor belts, carrying continents with them.

Hess believed, at the mid-ocean ridge, Molten material rises up from the mantle and erupts!

The molten material then “spreads out” pushing older rock to both sides of the ridge.

Every good “theory” has a name. Hess named his

• During this process, the cooled molten material SPREADS OUT on the SEA FLOOR and forms a solid rock.

• This continually adds new material to the ocean floor.

Much like Wegner, Hess had three kinds of evidence to support his theory; Molten Material, Magnetic Stripes, and Drilling Samples

Evidence #1 - Molten Material• The submersible, Alvin,

found strange rocks shaped like pillows or like toothpaste squeezed from a tube.

• Such rocks can form only when molten material hardens quickly after erupting under water.

• The presence of these rocks showed that molten material has erupted again and again.

Evidence #2 - Magnetic Stripes

What direction does the needle on a compass point?

Believe it or not, it hasn’t always. Evidence shows that the Earth’s magnetic poles have reversed themselves over the years.

If that happened today, compass needles would point.

Evidence #2 - Magnetic Stripes• Scientists discovered

that the iron in the rocks that makes up the ocean floor always line up in the direction of the magnetic pole when it cools.

• Scientists recorded the magnetic memory of rocks on BOTH sides of the ridge and found MATCHING “stripes” that hold a “magnetic memory”

Evidence #3 - Drilling Samples

• The Glomar Challenger did a drilling sample and found rocks that the farther away from the ridge the older the rocks were. The younger ones were in the center of the ridge.

DENSITY = Mass/Volume• Density- AGAIN???

• Yes, Density won’t go away.. It keeps popping up!

• Do you remember hot/cold water? Which one was more dense? (Think…This is the one that rises to the top)

• Hot/Cold Gases (like steam in your shower are the same.

• Is less dense than

• Think about the oceanic crust..

• New crust (just formed from MAGMA) is HOT!

• Old crust has cooled and is COLD!

• Which is more dense?

Subduction at Deep-Ocean Trenches• This density difference causes an interesting phenomena

called Subduction.• The cold crust (more dense) sinks to the bottom and back

into the mantle. (This process takes tens of millions of years)• The result is a constant motion (like Hess’s conveyor belt)

Subduction in the Pacific & Atlantic

• Deep ocean trenches are swallowing more oceanic crust than the mid-ocean ridge can produce. Thus, the width of the Pacific will shrink.

• The Atlantic is expanding. It has short trenches. In some places, the oceanic crust is attached to the continental crust which moves the continents.