Case Study: A Historical Perspective

The vastness of the ocean and the secrets of the submerged landscape contribute to its mystery. Seawater is opaque to light beyond a few hundred meters' penetration. Hence, there are no mountaintops one can scale to directly gaze at vast expanses of the abyssal seafloor.

- William B. F. Ryan, on the problems of mapping the seafloor

History of Seafloor Mapping

The earliest form of navigation on the sea was to keep within constant view of the land. Coastlines where ships sailed regularly were shown in clear detail on maps. Map makers simply guessed at the shapes of other coastlines. Source: National Oceanic and Atmospheric Administration, U.S. Department of Commerce
As a student of marine geology, one of the first things to learn is how we know what we know about the shapes of coastlines and the seafloor. Browse through the following timeline of ocean exploration efforts to find out how humans have developed techniques for mapping coastlines and the seafloor.

Early History

  • Around 300 BCE (Before Common Era), Alexander the Great compiled charts and documents about the oceans into the first library of marine science in Alexandria, Egypt.
  • By 600 CE (Common Era), Polynesians had colonized nearly every inhabitable island in the southern Pacific Ocean. Their navigation relied on observations such as wave motion against ships' hulls, flight tracks of birds, and distant clouds over potential land.
  • The Chinese invented the rudder, watertight hulls, and sophisticated sails on multiple masts.

The 1700s

  • The British Longitude Act of 1714 offered a large cash prize for anyone who could solve the "longitude problem."
  • In 1725, when fishermen could not "find" the seafloor, they assumed that the sea was bottomless. This highlighted the need for suitably equipped research vessels to map the seafloor.
  • In 1768, Captain James Cook set out on an exploratory voyage around the world. His voyage produced highly accurate maps and charts of islands in the Pacific as well as reports on marine life, geological formations, and ocean floor types.

The 1800s

First Bathymetric Map
First attempt at a bathymetric map showing depths of the Atlantic Ocean. Published by Matthew Fontaine Maury in 1855. Source: NOAA
  • In 1807, President Thomas Jefferson authorized the formation of an agency to survey the United States coastline.
  • The ocean bottom was thought to be very old. In 1832, a well respected geologist hypothesized that a wide range of the artifacts of past civilizations would be found on the seafloor once we had the technology to explore it.
  • In 1840, a depth measurement (sounding) was taken with a line of 2,425 fathoms (14,550 feet).
  • In 1867, deep dredge hauls yielded baskets full of living creatures. This disproved the common belief that the sea floor was void of living organisms.

The early 1900s

One of the earliest diagrams of echo-sounding in a published work. Source: F. Spiess' Die Meteor-Fahrt Forschungen, The Meteor Expedition (1928) by F. Speiss.

  • Echo sounding was invented. This technology measured the depth of the seafloor by generating sound pulses and measuring the amount of time they took to reflect back from the ocean bottom.
  • In 1960, two men in a manned submersible visited Earth's deepest ocean depth in the Marianas Trench.
  • A major development of the 1950s was the invention of the Precision Depth Recorder (PDR) at the Lamont Geological Observatory of Columbia University.
  • The discovery of a rift valley in the center of the mid-Atlantic ridge was one of the most important bathymetric discoveries ever made for developing the theory of plate tectonics. However, the discovery and its significance was not recognized for a year.

The 1960s

  • The three great tools of ocean exploration were invented in the '60s: the Deep Tow instrument system, multibeam sounding instruments, and research-capable manned submersibles.
  • The first Deep Tow instrument system was developed by Scripps Institution of Oceanography. It was tethered to a surface vessel then lowered and towed along just above the seafloor to collect and record information.
  • Multibeam sounding instruments that collect depth information along a swath of the seafloor instead of along a single line were the second major development of this period.
  • Improvements to manned research submersibles opened new worlds to human view. The Alvin submersible allowed scientists to explore ocean ridge systems. There, they discovered previously unimaginable communities of life that draw nourishment from the mid-ocean ridge environment.

Modern Era

  • The U.S. Geological Survey collects data from a variety of instruments to map the sea floor and its underlying geology. (Image provided by USGS).

  • Detailed satellite measurements that show small differences in ocean height have enabled scientists to develop a large-scale map of the ocean floor for most of our planet.

At the top of this page, you read a quote by William B.F. Ryan in which he focused on the problems of trying to measure and visualize the ocean floor. His quote actually ends by describing a solution to the problem that has been solved using today's technology:

... We visualize the hidden seascape with digital data sets, picture element by picture element, as tiles of a growing quilt, each stitched in the course of month-long expeditions.

-William B. F. Ryan (1992) "An Introduction - Down to the Sea in a Ship" Oceanus, Woods Hole Oceanographic Institution, MA