The Missing Piece

About 150 million years ago, during the breakup of a supercontinent that geologists call Gondwanaland,* South America and Africa began to drift apart, creating the Atlantic Ocean. There is convincing evidence for the once controversial theory that the two continents were once joined; geological features and fossil remains on opposite sides of the ocean show a remarkable match, and the shelves, or underwater plateaus, extending from each of the continents into the Atlantic form a near perfect fit, like adjacent pieces in a jigsaw puzzle. One piece of the puzzle, however, seemed to be missing. There was a deep indentation in the Mozambique plateau off Durban, South Africa, but no proof of a corresponding continental projection from South America. Last month it was announced that the missing land mass had been found; it is a fingerlike extension of the Falkland plateau, extending eastward from the Falkland Islands to a point 1,600 miles from Argentina.

Geologists Ian Dalziel of Columbia University and Peter Barker of the University of Birmingham led a multinational scientific team aboard the research ship Glomar Challenger this spring, probing the ocean depths east of the Falkland Islands. Lowering a coring drill 8,500 ft. to the bottom, they penetrated through 1,835 ft. of sediment before beginning to bite into the solid rock that they were looking for. Analysis of the core samples brought to the surface identified it as granite about 600 million years old. The find proved that the rock was continental shelf and not ocean basin crust, which is primarily basalt (solidified lava), which in the South Atlantic is no more than about 130 million years old.

From examination of fossils in the sediment cores found just above the bedrock, the geologists deduced that 150 to 200 million years ago, the Falkland plateau was dry land in a climate similar to that of the Mediterranean today. That evidence fitted in with earlier suggestions by other geologists that there had once been an inland sea in Gondwanaland similar to the Mediterranean and bounded by what are now South America, Africa and Antarctica. Then, as the continents began to separate, the area round the ancient sea gradually sank, reached its present depth about 80 million years ago, and remained hidden until the spring voyage of the Glomar Challenger.

Last week the Glomar Challenger again made news. Another team of geologists announced that in July a drill lowered from the ship in midocean, about 200 miles southwest of the Azores, had penetrated 1,910 ft. into the earth's hard crust under the Atlantic bottom sediment. It returned core samples from depths never before explored; the previous record penetration was 260 ft. into the submarine crustal rock. Said Geochemist William Melson of the Smithsonian Institution: "It was like probing into the unknown, getting samples we had thought about for years but had never been able to reach."

--Named after a region in India where many African-type fossils are found.

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