Ocean Ridges and Trenches

Plate Motion and Surface Features

Mid-Ocean Ridges

• Used to think the ocean floor was flat.

• Harry Hess used sonar to discover there were mountain ranges, canyons, and deep trenches.

• Long system of mid-ocean ridges extends around the world.

Harry Hess Discoveries

• Analyzed core samples of the sea floor.

• Ocean floor becomes OLDER as you move FURTHER from the ridge.

• YOUNGEST ocean floor is CLOSEST to the ridge.

Multiple Choice

Who first began studying the ocean floor?

• Albert Einstein

• Isaac Newton

• Harry Hess

Multiple Choice

Underwater mountain ranges, canyons, and trenches that extend around the world

• Mid Ocean Ridges

• Volcanoes

• Faults

Multiple Choice

Where did Harry Hess discover the YOUNGEST seafloor was located?

• Furthest from the ridge

• Closest to the ridge

Expanding Seafloor

• Ocean floor is made from cooling lava.

• Lava comes from the MANTLE at the ridge and cools.

• As more lava erupts, the crust moves away from the ridge.

• This is called SEAFLOOR SPREADING

What about the Old Ocean Floor?

• Old ocean floor moves edges of continents

• Trenches push ocean floor back to mantle

• RECYCLED!

• SUBDUCTION: crust pushing down into the mantle

Multiple Choice

The seafloor is recycled.

• True

• False

Multiple Choice

The crust going back down into the mantle is known as....

• Repurposing

• Transformation

• Subduction

Continental Drift

• Hess's idea of sea floor spreading proved Alfred Wegener's idea of CONTINENTAL DRIFT.

• 1960 - THEORY OF PLATE TECTONICS

• The Earth's LITHOSPHERE or CRUST is divided into tectonic plates.