Lesson 30
Exploring the sea-floor
How did people probably imagine the sea-floor before it was investigated?
Our knowledge of the oceans a hundred years ago was confined to the two-dimensional shape of the sea surface
and the hazards of navigation presented by the irregularities in depth of the shallow water close to the land.
The open sea was deep and mysterious,
and anyone who gave more than a passing thought to the bottom confines of the oceans probably assumed that the sea-bed was flat.
Sir James Clark Ross had obtained a sounding of over 2, 400 fathoms in 1839,
but it was not until 1869, when H.M.S. Porcupine was put at the disposal of the Royal Society for several cruises
that a series of deep soundings was obtained in the Atlantic and the first samples were collected by dredging the bottom.
Shortly after this the famous H.M.S. Challenger expedition established the study of the sea-floor
as a subject worthy of the most qualified physicists and geologists.
A burst of activity associated with the laying of submarine cables
soon confirmed the Challenger's observation that many parts of the ocean were two to three miles deep,
and the existence of underwater features of considerable magnitude.
Today, enough soundings are available to enable a relief map of the Atlantic to be drawn
and we know something of the great variety of the sea bed's topography.
Since the sea covers the greater part of the earth's surface,
it is quite reasonable to regard the sea floor as the basic form of the crust of the earth,
with superimposed upon it the continents,