They say we know more about the moon than about the deep sea—they're wrong

"We know more about the moon than the deep sea."

This idea has been repeated for decades by scientists and science communicators , including Sir David Attenborough in the 2001 documentary series The Blue Planet . More recently, in Blue Planet II (2017) and other sources, the moon is replaced with Mars. As deep-sea scientists, we investigated this supposed "fact" and found it has no scientific basis. It is not true in any quantifiable way .

So where does this curious idea come from? Mapping the deep The earliest written record is in a 1954 article in the Journal of Navigation, in which oceanographer and chemist George Deacon refers to a claim by geophysicist Edward Bullard. A 1957 paper published in the Journal of the Royal Society of Arts states: "the deep oceans cover over two-thirds of the surface of the world, and yet more is known about the shape of the surface of the moon than is known about that of the bottom of the ocean." This refers specifically to the scant amount of data available on the topography of the sea floor and predates both the first crewed descent to the deepest part of the ocean, the Mariana Trench (1960), and the first moon landing (1969).

Credit: Alan Jamieson Read more

Almost a quarter of the world’s seafloor has been mapped in detail. Credit: GEBCO Read more

The bathyscaphe Trieste was the first crewed vessel to reach Challenger Deep, in 1960. Credit: US Navy Read more