Geology of the Ocean
By Katie Wallace & Sarah Turcotte
 Slide two - The study of the ocean floor is known as geological
oceanography.
 Slide three - The bottom of the ocean can be separated into four main areas:
the continental shelf, the continental slope, continental drift, and the deep
sea basin.
The theory of continental drift and the movement of the tectonic plates are
also very important in geological oceanography.
Picture quote: “Seafloor spreading is the theory that explains how the floors
of oceans had split apart and rocks on either side of the ridges are moving
away from each other”
 Slide four - Continental Shelf
The continental shelf is located between the continental slope and
the coastline. It surrounds all the continents of the world. The shelf is more
than 100m deep, and they can reach at most a distance of 1500km off the
coastline. They can either be passive or active. The continental shelf and
continental slope make up the continental margin.
 Slide five - Passive vs. Active?
The passive continental margin runs alongside the coast of North
America and it is generally very flat and very wide. There is no volcanic
activity in this area and earthquakes can happen, but are very rare.
Active continental margins aren't flat or wide and they are located in
subduction zones. A subduction zone forms when two of the earth’s
tectonic plates collide. One plate slides beneath the other because the plates
are always moving. There’s lots of volcanic activity in active areas and
earthquakes occur regularly.
 Slide six - Continental Shelf and Beyond…
As the continental shelf gets steeper the water depth increases faster,
and the continental slope is formed. The slope reaches a depth of around
3700m, and anywhere past that is considered to be part of the deep ocean
basin. In the deep ocean basin, the depth increases, and the mid-oceanic
ridge begins. The mid oceanic ridge has the largest undersea mountains.
 Slide seven – Mid-Oceanic Ridge
The mid-oceanic ridge is like an underwater mountain range. The
mountains can reach a height of up to 3000m and the can be around
2000m wide. There are deep trenched that are located in the center of the
mid-oceanic ridge; it divides the mountain ranges right down the center.
These trenches reach depths no less than 2000m, and have the most heat
flowing through them because they are so deep. Most earthquakes occur in
these ridges.
 Picture A close-up showing of a mid-ocean ridge with magma
rising from a chamber below, forming new ocean plate which
spreads away from ridge. Magma contains molten rock,
suspended crystals and dissolved gas and sometimes also gas
bubbles.
 Slide eight – Deep Sea Trenches
Deep sea trenches have the deepest waters and can reach depths of
35000 feet from the surface of the ocean. They can be sometimes related to,
or be located right beside continental mountain ranges. There are 26 deep
sea trenches all together.
 The Mariana Trench is the deepest part of the world's oceans. It
is located in the western Pacific Ocean, to the east of the
Mariana Islands. The trench is about 2,550 kilometers and
reaches a maximum-known depth of about 10.91 kilometers
 Slide nine – Continental Drift and Plate Tectonics
German meteorologist, Alfred Wegner, suggested that all the
continents of the world were once joined together, making one
supercontinent, which he named Pangaea. He realized that rock formations
located on either side of the Atlantic Ocean were identical in age, structure
and type. There were also fossils of the same creatures found in both rock
formations. He concluded that Pangaea began to separate around 200
million years ago. This is the theory of continental drift.
Continental drift and plate tectonics go together. Plate tectonics
explains how Pangaea became all the continents we know today
 Animation of the break-up of Pangaea and the formation of
modern continents.
 Slide ten – There are four main points to plate tectonics :
1. The earth’s surface is located on top of tectonic plates.
2. The ocean floors are in constant motion because they are on
top of the plates.
3. There are convection currents beneath all the plates. This
causes them to be in constant motion. Convection currents: are
caused by the movement of lava in the mantle. The lava is
moving from heated zones to cooler zones. The ocean isn’t the
only things that have currents!
4. The heat source that causes convection currents is located
deep in the earth’s mantle. Mantle: is made of super heated
rock, and it comes before the outer core of the earth.
 Slide eleven – Here is a short video from YouTube illustrating the
movement of the tectonic plates and the formation of all the continents
over millions of years
 Slide twelve – Work cited