Geology Reference
In-Depth Information
A dramatic breakthrough occurred during World War I when the use of submarines led
to mapping of the seafloor. Eureka! Marine geologists discovered a long, rocky ridge, a
rift, in the middle of the Atlantic Ocean. Along this rift they recorded earthquake activity,
and other scientific studies (described in Chapter 8) provided evidence that the rocks
close to the rift were younger than rocks farther away from the rift. These observations
suggested that the seafloor was spreading apart along this rift.
By 1928, the idea of seafloor spreading — the moving apart of oceanic crust along ridges
on the ocean floor — was being explored by scientists. But there were still many who
“knew” the earth's crust and the mantle below were solid rock and could not be moving.
Research continued for the next few decades, and in the 1960s a revolution in geologic
thought took place: the formation of a unifying theory for geology. The theory of plate
tectonics combines ideas about plate movement with evidence for seafloor spreading, as
well as incorporating explanations for volcanoes, earthquakes, and other geologic fea-
tures and phenomena. Because this theory is so crucial, I devote Part III of this topic to
it.
Scientists never stop exploring, of course, so even with a well-accepted, well-tested ex-
planation of how the surface of the earth constantly transforms, they don't stop asking
questions.
Forging Ahead into New Frontiers
After geologists had the theory of plate tectonics laid out, they had a framework within
which they could propose and test specific hypotheses to fill in the details. This work
continues today, right now, as you read these words! The frontiers of earth science are
being expanded in many directions. In this section I describe just a few areas of current,
exciting research and discovery.
Asking how, where, and why: Mountain building
and plate boundaries
Plate tectonics theory explains that the movement of plates creates mountains by push-
ing crustal rocks together and up (see Chapters 9 and 10). But scientists have not
gathered enough evidence to agree on what forces drive the uplift of mountains. Some
suggest that a pushing force, exerted by the neighboring plate, forces the rocks upward.
Others suggest that the removal of rocks by erosion (explained in Part IV) leads the con-
tinental rocks to “float” upward, like an iceberg melting in the ocean.
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