A century ago, the shape of the ocean bottom was a mystery. Scientists lacked a good way to investigate it.

They could only measure depths with a weighted line, and this was done in just a few places, because lowering and raising the line took a lot of time and effort.

And yet, by feeling in the dark North Atlantic with their line, the scientists did detect an important feature.

This was a mountain range rising from the middle of the ocean floor. Recently, scientists devised a much better method of exploration, called echo sounding.

An instrument on board ship makes a series of ‘pings’-sound impulses that speed through the water in the form of compression waves.

These waves hit the bottom, echo back, and record their travel time in the form of a line. The line goes up and down, following the shape of the bottom.

Rift in the Ocean Floor:

Scientists crossed and re-crossed the Atlantic taking profiles with the echo sounder.

Working from these profiles, they were able to map the whole bottom. When their map was finished, it revealed a tremendous hidden feature of the Earth-a great long ridge of mountains running the entire length of the Atlantic.

The ridge divides the ocean basin into a western half, bordered by the Americas, and an eastern half, bordered by Europe and Africa.

The profiles show that the ridge is split down most of its length by an enormous rift, deeper and wider than the Grand Canyon of the Colorado River.

The ridge rises about miles from the ocean floor, with summits reaching to within a few thousands feet of the surface.

Several peaks emerge above the surface as islands. Among these are the Azores, which are the tops of old volcanoes.

Another high portion of the ridge forms Iceland, a lava plateau that is still growing as volcanic eruptions build it up.

The ridge follows a very active seismic zone. Of all the Earthquakes traced to the Atlantic basin, nearly all occur in this zone.

The shocks come from the rather shallow depth of 18 miles. Evidently, the Earth’s crust under the ridge is disturbed by forces that continually break it, causing Earthquakes and lava eruptions.

Similar ridges have recently been found crossing the floors of the other oceans. These ridges, too, mark zones of Earthquake activity.

In fact, they were discovered by taking profiles across seismic zones. The ridges of the several oceans link into one connected system 40,000 miles long, forming the Earth’s third great feature, after the ocean and the continents.

Continents Adrift