Review Sheet – Chapter 2
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Know that the oceans cover 71% of the Earth
Know that the average depth of the ocean is 3,800 meters
Understand that the oceans and continents are not distributed evenly and that the oceans
dominate the Southern Hemisphere, while the continents dominate the Northern Hemisphere
Know the 5 oceans, and be able to locate them on a map
Understand that gravity pulls denser, heavier materials/elements towards its center, while
lighter (less dense) materials are found near the surface
Understand that there are chemical and physical differences between oceanic crust and
continental crust
Know that oceanic crust is made up of basalt and is thin, dense and dark
Know that continental crust is made up of granite and is thick, less-dense, and light in color
Understand that oceanic crust sinks deeper into the mantle than continental crust
Understand that the oldest oceanic crust is 200 million years old, while the oldest continental
crust is ~3.8 billion years old (about the age of the Earth)
Know that the theory of continental drift was originally conceived because of the coincidence in
shape of the Atlantic coasts of South America and Africa
Know that the theory of continental drift was proposed by Alfred Wegener, and theorized that
all Earth’s land was once joined in a supercontinent known as Pangaea
Understand that the theory of plate tectonics states that the Earth’s upper layer – the
lithosphere – is broken up into pieces, or plates that float and drift over the molten
asthenosphere
Understand that seafloor spreading describes the large-scale movement of the continents and
helps explain the presence of mid-oceanic ridges and the creation (and destruction) of new
oceanic crust
Know that seafloor spreading in the Atlantic Ocean occurs along the Mid-Atlantic Ridge
Understand that the newly-formed oceanic crust is very warm and so less dense than the
surrounding (older and thus cooler) oceanic crust. Understand that as a result, the newlyformed crust rises above the older crust in the form of a mid-ocean ridge (new oceanic crust
does not sink as deeply into the asthenosphere as older oceanic crust).
Understand that as oceanic crust is being laid down at the center of ocean basins, it is also being
destroyed at continental margins, via a process known as subduction.
Understand that during subduction, the dense oceanic crust sinks beneath continental crust and
is destroyed in the process
Understand that the process of subduction explains why we do not see oceanic crust nearly as
old as continental crust (which is very rarely destroyed)
Know that when 2 oceanic plates converge, the older (and so cooler), denser plate subducts
beneath the newer (and so warmer), less dense plate, forming a very deep trench
Know that when 2 continental plates converge, neither plate subducts, but rather both plates
compress and uplift forming mountain ranges
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Know that the Marianas Trench was created by 2 oceanic plates converging together, and is the
deepest trench in the world
Understand that volcanic islands such as Hawaii and the Galapagos are not created by
convergence or subduction, but rather by a plate moving across a stationary mantle plume
Know that continental margins are submerged portions of continental crust, while deep sea
floor is composed of oceanic crust
Know that continental margins consist of a gently-sloping continental shelf, a steep continental
slope, and the continental rise – the junction between continental and oceanic crust
Know that continental shelves are the biologically richest parts of the ocean
Understand that the abyssal plain is deep sea floor that slopes very gently towards the midoceanic ridge
Know that at the center of the mid-oceanic ridge lies a central rift valley
Know that hydrothermal vents release superheated water containing dissolved minerals such as
sulfides and host a unique assembly of marine organisms