Due to low temperatures, lack of light, and pressure, the majority of the ocean floor is inhospitable to humans. However, technological advances have enabled scientists to map areas of the ocean floor. This technology is based on the same principal used by bats and beluga whales for getting around—sound waves and echoes. Sonar monitors and measures echoes to determine the distance to an object. Interest in sonar technology was largely influenced by war efforts during the early 20th century. The need to detect enemy submarines advanced sonar to a point where remarkable sea-floor topography was discovered.

Mid-Ocean Ridge

Before the invention of sonar, very little was known about the ocean floor. Early line sounding devices, which were weights attached to spools of rope, uncovered some elevation differences that lead people to believe the ocean floor had a varied topography. The development of sonar technology in the early 20th century confirmed this and uncovered more mountains along the sea floor. The discovery of the mid-ocean ridge, a mountain range at the bottom of the ocean, sparked great interest in the field of oceanography because it generated many questions. How does a feature of this size form on the ocean floor? What geologic processes are happening?

Today, Dr. Walter Smith's maps of the ocean floor show us that the mid-ocean ridge curves through all the oceans of the world like the seams of a baseball. Running down the middle of this mountain range is a valley called a rift.

Sea-floor Spreading

American geologist Harry Hess was very interested in mid-ocean ridges. He thought that by understanding how the mid-ocean ridge formed, he could finally discover the mechanism behind continental drift.

In 1960, Hess proposed the idea of sea-floor spreading. He hypothesized that the rift that runs like a spine down the middle of the mid-ocean ridge is a continuous series of vents, or cracks in Earth's crust. These openings enable lava to erupt from the mantle. As hot lava erupts into the cool sea water, it instantly cools and hardens, becoming new oceanic crust. Over time, successive eruptions push older solidified rock outwards, gradually spreading apart the mid-ocean ridge and moving continents. This was a remarkable theory, but at the time, nobody was able to find proof that lava was erupting from the rift of the mid-ocean ridge.

Finding the Proof

During more than 120 underwater expeditions, Dr. Bob Ballard has explored the changes happening on Earth that have been occurring for millions of years. In 1977, while investigating a small section of the mid-ocean ridge near the Galápagos Islands of Ecuador, he discovered a key piece of evidence to explain how and why the continents moved.

Venturing 2.7 km (1.7 mi) deep into the ocean and engulfed in total darkness, Dr. Ballard was searching for volcanic heat that could explain the formation of mid-ocean ridges. His team discovered what looked like the giant pipes of a church organ. These pipe-like structures, hydrothermal vents, continuously spewed darks clouds of minerals reaching temperatures of 350°C (662°F)! The high temperatures indicated that the rift was where the sea floor was literally being ripped apart and molten rock erupting through the surface to was forming new earth. Bob Ballard's discovery has helped shape our current understanding of how continents move, why earthquakes occur, and where and when volcanoes erupt.