Chapter 3: Plate Tectonics Lesson 2: Sea-Floor Spreading
New ______ material from inside Earth rises along the _____ and eventually cools and hardens to form solid ____.
molten, ridge, rock
The ridges form the longest ________ ______ on earth.
mountain ranges
In sea-floor spreading, new crust is added to the _____ _____. Older strips of rock then move _______ from either side of the ridge.
ocean floor, outward
Mid-ocean ridges run along the ______ of some ocean floors.
middle
a deep valley along the ocean floor beneath which oceanic crust slowly sinks toward the mantle.
deep-ocean trench
Scientists have found three different types of evidence to support the theory of sea-floor spreading: A. Pillow shaped ____ _____ found in the valleys of the ridges proves that molten material exists there. B. The pattern of ________ _____ in rocks on either side of a mid-ocean ridge is the same. C. Drilling samples show that the youngest rocks are always found at the ______ of the ridges.
lava rocks, magnetic stripes, center
Mid-ocean ridges form ____ ______ __ _________ ____ _____ __ ____ ___ _____ _____.
long chains of mountains that rises up from the ocean floor
an undersea mountain chain where new ocean floor is produced.
mid-ocean ridge
The oceanic crust created along a ______________ is destroyed at a ________________.
mid-ocean ridge, deep-ocean trench
The process of sea-floor spreading begins at a _________ ______ where a _____ is formed.
mid-ocean ridges, crack
Subduction occur because: A. New oceanic crust moves away from the _______________ and cools. B. As it cools it becomes more _____. C. As it moves, the cool, dense crust may collide with the edge of a _________. D. _______ then pulls the older, denser oceanic crust down beneath the ______ and back into the mantle again.
mid-ocean ridges, dense, continent, gravity, trench
_______ crust bends downward at deep-ocean trenches so that part of the ocean floor sinks back into the ______.
oceanic, mantle
the process by which molten material adds new oceanic crust to the ocean floor.
sea-floor spreading
the process by which oceanic crust sinks beneath a deep-ocean trench and back into the mantle at a convergent plate boundary.
subduction
Some mid-ocean ridges have a ______ that runs along their center.
valley