National Geographic : 1948 Sep
Exploring the Mid-Atlantic Ridge 279 From the ocean floor three miles below the . surface, this flat-topped mountain rose grad ually and then moresteeply toaheight of about two miles (map, pages 280-281). At a point near its center we decided totry to get a sample of the bottom (pages 288-9). The depth was 841 fathoms, orabout amile. _ Using our big winch and cable, we lowered .. a coring tube. Thissteel pipe, 2/2 inches in diameter and about10feet long, brings up samples of the oceanfloor just as ahousewife I cores an apple. A hardened-steel cutting edge I was screwed on thebottom ofthe tube and I about 1,000 poundsoflead weights were at- I tached to the top todrive itinto the bottom. I To penetrate far, this tube must fall freely I during the last partofitsdescent. Accord- I ingly, a trigger hangs several feet below the I end of the tube. When the trigger touches I bottom, it releases aclamp holding the coring I tube to the wire andpermits afree fall. 1 Core Spans Millions ofYears To our astonishment, when we examined this core later in ourlaboratory atColumbia University it was found tohave spanned millions of years. Itcontained two distinct I layers. I The top eight inches proved tobearecent I| deep-sea sediment typical ofallthe ocean I bottom far from land where the depth isless I than 2,500 fathoms (nearly three miles). This sediment, called globigerina ooze, was dark cream-color and coarse grained, being rich in shells of the one-celled marine organisms called foraminifera. The remainder ofthe core was white and much finer-grained. Study showed ittobe a fine-grained chalkcontaining foraminifera of Eocene age. This meant that aninterval of60million years had gone by between the deposition of the chalk in the bottom ofthe core and the top eight inches ofooze and added greatly to the mystery of the origin and history of the sea mount. So far as I know,this isthe first time that sediments older than afew thousand years have been recoveredfrom considerable depths in any ocean basin. Our discovery of open-ocean sediments of Eocene age on a sea mount near Bermuda, far to the west of the Mid-Atlantic Ridge, is hard to reconcile with the Wegener theory of the formation of the Atlantic Ocean. Ac- Drawn byIrvin E.Alleman cording to that theory, advanced by the late Back from Bottom Comes an Eloquent Echo German scientist Alfred Wegener, the At- Asediment layer more than 500 feet thick gives lantic Basin was formed by the "drifting a"double echo." The difference intime between the two echoes indicates its thickness (page 280). To apart" of the continents upon the molten in- show toscale this depth of2% miles, the page would terior of the earth, and the Atlantic Ocean inhave tobe7feet long.