Welcome to You Ask Andy

Steven Bergen, age 12, of St. Catharines, Ontario, Canada, for his question:

How was the Pacific Ocean formed?

The most ancient chapters of our planet's formation are shrouded in mystery. Scientists suspect that the earth and the moon shared a similar early history. Some of these secrets may be solved by the samples of lunar minerals. They proved that the moon is 4 1/2 billion years old and we can assume that the earth is about the same age. The study of lunar geography also may help to solve other problems on earth    and possibly give us a few clues on how our vast ocean basins were formed.

The evidence suggests that the earth always had deep ocean basins and uplifted land masses. There is also a lot of evidence to indicate that the land and sea areas have done a lot of changing on a global scale. The waters of the vast Pacific are more or less contained in one of several steep sided basins in the earth's crust. These deep hollows may or may not have been remodeled as the globe trotting continents wandered around. Earth scientists are still trying to trace this wanderino, geography. And so far, no one can say for certain how the original continents and ocean basins were formed.

This, of course, does not stop scientists from speculating. Several theories have been suggested. Several years ago, one theory suggested that the moon was torn from the infant earth when it was in a more or less molten state, leaving a great hole that became the Pacific Ocean. But this dramatic idea was discredited    even before the lunar rocks proved it to be false.

The more likely theories are all based on studies of the earth's crust and its structure. After all, both the oceans and continents are part of the crust, which is actually in two somewhat different layers. The lower layer forms the ocean floors and lies under the continents. It is about three miles thick. The continents are made of lighter materials and float, so to speak, on the denser layer below. Both layers of the crust are made mostly of volcanic materials.

The Pacific basin is an immense hollow in the earth's crust. One tends to think of a hollow as something scooped out of the ground. But it is more likely that the lighter continents were forced up from the lower crustal layer, leaving the ocean basins around them. Whether this did or did not happen involves detailed studies of the structure of the crust, gravity and other forces at deeper levels, plus massive data on minerals  and their behavior under intense heat and pressure. One theory stresses the  discontinuity revealed by earthquake vibrations. This is a sudden change in density that occurs at definite depths in the crust. Calculations suggest that it occurs where there is a certain ratio of heat and pressure. It may prove to be a critical ratio that triggers dynamic activity in the lower crust. Possibly this or some other factor caused dense masses in the lower level to become lighter and rise to form the continents.

A present, we have no positive answers. But it is not likely that the Pacific basin was scooped from the earth's crust. Possibly the lower layer that holds the oceans gave birth to the uplifted continents. But no one can prove how this could have happened. However, if you plan a career in the earth sciences, you can be sure of one item. The earth will offer you plenty of mysteries to solve.

 

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