For centuries, people have been challenged by the mysteries that lie beneath the blue depths of our ocean planet. Very little was known about the ocean until late in the nineteenth century, although nearly three-quarters of the planet is covered by ocean or seawater. Myths and misconceptions abounded. We used to think that the ocean depths were devoid of life. We thought that the seafloor was flat and that it was the same age as the continents. How different a picture we now have of the ocean as the sea has begun to yield its secrets.
In the 1870s, the HMS Challenger left England and sailed the world's oceans, throwing out weighted lines and taking soundings to measure the depths of the Atlantic, Pacific, Indian, and Arctic Oceans. For the first time, scientists had an inkling of the contours of the ocean floor, took samples of the plants and animals, and measured differences in water temperature and salinity. But the cold, dark water and extreme pressure of the depths kept scientists from knowing the secrets of the deep abyss.
Following in the footsteps of those pioneering oceanographers, today's scientists have overcome many of the challenges of the deep by using more sophisticated tools. They can send manned submersibles and sampling devices to plumb the ocean depths, taking photographs and samples of animal life and sediment to bring back to the surface for further study. Even space technology enters the picture. Satellite photos taken of the ocean provide a wide range of information, including water temperature and depth, seafloor topography, and the plankton populations. Using sonar and satellite data, scientists have been able to generate a new map of the ocean floor, thirty times more accurate than the best previous map. This map shows the ruggedness of the Mid-Ocean Ridge as it bisects the Atlantic Ocean. This contrasts to the relatively flat Pacific Ocean floor, its vast expanse broken up by more than a thousand newly discovered underwater volcanoes stretching from Hawaii to the Aleutians.
And to what does this vast treasure trove of data lead? For scientists, there is a broader understanding of how the ocean basin formed and continues to evolve. Molten magma from Earth's interior spews out at the mid-ocean ridges, spilling over to either side and hardening to rocky basalt. As the crust pushes away from the ridges, it cools and thins, forming new seafloor and thus "widening" the ocean here. As this portion of the ocean floor widens, a section of the seafloor elsewhere is slowly sliding beneath the crust, becoming part of Earth's magma once again. Plate tectonics, the theory of Earth's crustal plates, thus helps explain ocean formation.
New observations also give scientists a greater understanding of the dynamic nature of Earth's water and oxygen cycles and how planetary winds affect ocean currents. Data allow scientists to hypothesize about global weather systems, earthquake and volcanic activity, and climatic trends of global consequence. Understanding the interactions of the ocean and marine life gives us an indication of the planet's health and the effects of human activity.
The development of new technologies for underwater exploration has led to exciting and lucrative expeditions. Photographs of the doomed Titanic taken by remote cameras from a submersible craft as it probed deep in the North Atlantic captured the imagination of the world. Recently declassified information about the locations of sunken World War II vessels has attracted adventurers and investors who would like to bring up rich cargoes. The old romantic notion of diving for Spanish pieces of eight from pirate shipwrecks in the Caribbean has been replaced by the idea of using sonar and other sensors to locate sunken submarines carrying gold. But whether in pursuit of knowledge or profit, all of these activities contribute to our understanding of the ocean.