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[ti:Exploring the Sea-Floor]

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[00:01.52]Lesson 30

[00:03.24]Exploring the sea-floor

[00:11.90]How did people probably imagine the sea-floor before it was investigated?

[00:20.08]Our knowledge of the oceans a hundred years ago

[00:23.21]was confined to the two-dimensional shape of the sea surface

[00:27.87]and the hazards of navigation presented by the irregularities in depth

[00:32.65]of the shallow water close to the land.

[00:36.48]The open sea was deep and mysterious,

[00:40.10]and anyone who gave more than a passing thought to the bottom confines of the oceans

[00:45.51]probably assumed that the sea bed was flat.

[00:49.62]Sir James Clark Ross had obtained a sounding of over 2, 400 fathoms in 1839,

[00:57.40]but it was not until 1869,

[01:00.25]when H.M.S.Porcupine was put at the disposal of the Royal Society for several cruises

[01:07.71]that a series of deep soundings was obtained in the Atlantic

[01:12.46]and the first samples were collected by dredging the bottom.

[01:17.08]Shortly after this the famous H.M.S.Challenger expedition

[01:21.56]established the study of the sea-floor

[01:24.00]as a subject worthy of the most qualified physicists and geologists.

[01:29.67]A burst of activity associated with the laying of submarine cables

[01:34.51]soon confirmed the Challenger's observation