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Developing the theory [This Dynamic Earth, USGS] (1866 words) |
 | In 1961, scientists began to theorize that mid-ocean ridges mark structurally weak zones where the ocean floor was being ripped in two lengthwise along the ridge crest. |
| Furthermore, the oceanic crust now came to be appreciated as a natural "tape recording" of the history of the reversals in the Earth's magnetic field. |
| As old oceanic crust was consumed in the trenches, new magma rose and erupted along the spreading ridges to form new crust. |
| Plate Tectonics: Sea floor (1890 words) |
| Seafloor spreading proposed that rising magma was forming new oceanic crust along the oceanic ridges and that old crust was destroyed at oceanic trenches. |
| Oceanic rocks along the North American and African coastlines are approximately 180 Myrs old whereas rocks adjacent to the ridge may be less than one million years old. |
| The presence of the older oceanic floor along the trenches was used to infer that the oceanic lithosphere was being consumed at the trenches. |
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