Vast oceans are actually thin layers covering the globe

Mar 29, 2016 by Scott McDowell

We all have a mental image of the mighty Atlantic – vast and abyssal with average depth of 2.4 miles and the Puerto Rico Trench exceeding 5 miles. Not surprisingly, the earth is called the Water Planet as 71 percent of its surface is covered by world oceans, adjacent seas and lakes.

Saline water makes up 96.5 percent of earth’s total water, while the small remainder is fresh water; either liquid or stored in ice.

Jumping topics for a moment – imagine a puddle 1 inch thick and 110 feet across. It would be a challenge to engineer a pool this thin, but nature has done it. Surprisingly, our Atlantic has exactly this ratio of its dimensions. At roughly 3,200 miles wide but only 2.4 miles deep, the Atlantic has a width-to-depth ratio of 1,333:1 – equivalent to the hypothetical puddle 1 inch thick and 1,333 inches (110-ft) across.

Here is an image representing all of the water on, in, and above the Earth. PHOTO/USGS

Here is an image representing all of the water on, in, and above the Earth. PHOTO/USGS

The Pacific Ocean has nearly twice the area of the Atlantic and its average depth is 21 percent greater than the Atlantic’s.

The Pacific’s width-to-depth ratio, 1,545:1, is comparable to the Atlantic’s ratio based upon an average depth of 2.9 miles and width of 4,400 miles. Consequently, the Pacific has physical scales equivalent to a 1-inch deep puddle that measures 129 feet across. Yes, our oceans cover most of the earth, but from a global perspective, they cover it in very thin layers.

Another way to appreciate the thin characteristic of our oceans is via comparison with a well-known sphere: an orange.

Most oranges have diameters of about 3 inches and a rind that’s 1/8th-inch thick. The radius of an orange is thus about 12 times the rind thickness.

In comparison, the earth’s radius (3,950 miles) is 1,650 times the thickness (depth) of the Atlantic draped over it.

The physical equivalent to this thin layer of water would be an orange having an exceptionally thin rind.

How thin? It would be about 1/5th the thickness of plastic food wrap. Our oceans are so thin they’re barely significant when you consider the volume and diameter of our planet.  

The name Water Planet is valid only when based upon visual characteristics.

The figure at top left, represents the volume of all water on the earth by the blue sphere, in proportion to the earth’s size.

As indicated, the volume of our oceans is only .012 percent of the earth’s volume or in other words, there is 800 times more solid matter on our planet than water.

In future articles I will describe fascinating ocean currents that slide around the globe at mid-depth and near-bottom levels while not having contact with the sea surface for thousands of years.

Scott E. McDowell has a doctorate degree in ocean physics, is a licensed captain and author of Marinas: a Complete Guide available at Contact him at




CORRECTION: Two equations in my prior article on wave speed were printed incorrectly.  Correct equations are given below:

Wave speed (ft/sec): S = where D = depth (ft);   G = gravity (32 ft/sec2)

Wavelength (ft): L = 5 * T2 where T is wave period (sec)


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