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Earth's Layers 4
6th Grade Science: Unit 5 - Sea-Floor Spreading
| Question | Answer |
|---|---|
| A mid-ocean ridge is an underwater mountain chain where new _______ is produced | oceanic crust |
| ________ was an American geologists who studied mid-ocean ridges | Harry Hess |
| Hess’s studies showed that Alfred Wegener would have been right about ________! | Continental drift (the continents drifting apart) |
| Describe Hess’s idea of sea-floor spreading. | new oceanic crust is continuously created at mid-ocean ridges, pushing the existing seafloor away from the ridge in both directions, essentially acting like a conveyor belt that moves the continents along with it; this process is driven by molten rock rising from the Earth's mantle along the ridges, creating new crust and causing the ocean floor to spread apart. |
| Name 3 types of evidence used to support seafloor spreading. | 1) molten material 2) magnetic stripes 3) drilling samples |
| Evidence from molten material: Scientists found strange rocks shaped like pillows or toothpaste squeezed from a tube. Such rocks only form when ___________. | molten material hardens quickly after erupting under water |
| Evidence from magnetic stripes: Scientists have discovered that the rock that makes up the ocean floor lies in a pattern of magnetized stripes. These stripes hold a record of ____________. | reversals in the Earth’s magnetic field because the rock contains iron |
| Evidence from drilling samples: Samples from the sea floor were brought up and dated. They found that the farther away from the ridge the samples were taken, ________________. | the older the rocks were. The youngest rocks were always in the center of the ridges. |
| Just as sea-floor spreads, it also plunges into deep underwater canyons called _____________. | deep-ocean trenches (during this process, the ocean floor bends downward and sinks back into the mantle) |
| At a deep-ocean trench, _______ occurs | Subduction |
| What is subduction? | Subduction is the process by which ocean floor sinks back into the mantle |
| The processes of ____________ and ___________ can change the size and shape of the oceans | subduction and sea-floor spreading |
| Because of subduction and seafloor spreading, the ocean floor is renewed about every ___ years | 200 million years |
| What is the mid-ocean ridge? | the longest chain of mountains in the world |
| What technology did scientists use in the mid-1900s to map the mid-ocean range? | sonar |
| In the process of seafloor spreading, where does molten material rise from the mantle and erupt? | along the mid-ocean ridge |
| How did scientists discover that rocks farther away from the mid-ocean ridge were older than those near it? | by determining the age of rock samples obtained by drilling on the sea floor |
| What did scientists in a submersible see when they observed the mid-ocean ridge? | rocks formed by the eruption of molten material from Earth’s mantle |
| The process by which the ocean floor sinks through a deep-ocean trench and back into the mantle is know as | subduction |
| If subduction occurs faster than oceanic crust can be created, an ocean will _______ | shrink |
| The formation of volcanoes and mountain ranges can be explained by the theory of ____. | plate tectonics |
Created by:
Engle Family
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