For centuries humans have looked to the skies and the space beyond as the greatest frontier for exploration. Having mapped most of the land on the planet, the next logical step for most is to go beyond the earth — to other planets and moons and, eventually, other solar systems and galaxies. What these dreamers forget is that while scientists have a fairly detailed understanding of the topography of the surface of the earth, more than seventy percent of the planet is under oceans and they have very little understanding of the topography of the ocean floor.
Scientists have devised several different methods for mapping the ocean floor. Early ocean exploration consisted of submarines exploring specific areas and mapping their findings. In 1951 the first survey of the Marianas Trench was completed by a British naval vessel. The Trench is considered to be the deepest point of any ocean, falling 10,923 below the surface of the Pacific Ocean. The depth was confirmed when, in 1960, a specially designed two-person vessel reached the actual bottom of the trench.
In 1995 scientists created a global ocean map that only included features larger than six miles (ten kilometers). This image was created by calculating the gravitational distortions these features created on the sea surface. Satellite mapping estimates the shape of the ocean floor by measuring the surface of the ocean and seismologists are able to use their instruments to calculate the thickness of sediment levels on the ocean floor.
The most accurate measuring system uses sonar. Ships and submarines send out sound waves to determine the depth and shape of the ocean floor as they travel over it. This type of survey is very time consuming. Each section of the sea must be traversed and mapped individually. Recent developments in sonar technology allow vessels to map larger areas using multiple beams. In such systems, a single ship can track a path as wide as fifteen kilometers. It would still take many decades to map the entire ocean floor in this manner, if an organized and systematic mapping project were devised. Instead, data is collected and shared from various sources, leaving large gaps between mapped areas. In most places, the gaps of uncharted ocean floor are larger than the charted areas, the average gap measuring 20,000 square kilometers of ocean floor.