Download "Inside Earth" Chapter 1 Section 4

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“Inside Earth”
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Topic:__
Name: _______First & Last____________________________
Class: _____Science____________ Period: ___All_____
Date: ____________October 2016________________
Chapter 1, Section 4: Sea-Floor Spreading
Essential Question:
How does the theory of plate tectonics explain the cycling of Earth’s materials and the flow of
energy that drives the process?
Notes:
Questions/Main Ideas:
Chapter 1, Section 4: Sea-Floor Spreading
Evidence for Sea-Floor Spreading
* Mid-Ocean Ridges are chains of volcanoes that wind
around Earth; the system is more than 50,000 km long.
Most of the mountains are deep underwater, but the
island of Iceland is a part of a mid-ocean ridge.
What is Sea-Floor Spreading?
* Harry Hess connected mid-ocean ridges to Wegener’s
hypothesis of Continental Drift.
* “In sea-floor spreading, the sea floor spreads apart
along both sides of a mid-ocean ridge as new crust is
added. As a result, the ocean floors move like conveyor
belts, carry the continents along with them.
Evidence for Sea-Floor Spreading
* “Several types of evidence supported Hess’s theory of
sea-floor spreading: eruptions of molten material,
magnetic stripes in the rock of the ocean floor, and the
ages of the rocks themselves.
* Evidence from Drilling Samples: rock farther from the
ridge is older; rock closer to the ridge is younger.
Subduction at Trenches
* In a process called subduction, which takes tens of
millions of years, part of the ocean floor sinks back into
the mantle at deep-ocean trenches.
Summary:
* The sea floor spreads apart along both sides of a mid-ocean ridge; new crust is
added. The ocean floors move like conveyor belts, carrying the continents along
with them.
* Evidence for Hess’s theory sea-floor spreading: eruptions of molten material at
mid-ocean ridges, magnetic patterns in the rock, and the ages of the rocks.
* Subduction happens at deep-ocean trenches (and elsewhere), where oceanic crust
sinks down into the mantle.