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The Geologic History of the Mediterranean

In 1970 geologists Kenneth J. Hsu and William B.F. Ryan were collecting

research data while aboard the oceanographic research vessel Glomar Challenger.

An objective of this particular cruise was to investigate the floor of the

Mediterranean and to resolve questions about its geologic history. One question

was related to evidence that the invertebrate fauna (animals without spines) of

the Mediterranean had changed abruptly about 6 million years ago. Most of the

older organisms were nearly wiped out, although a few hardy species survived. A

few managed to migrate into the Atlantic. Somewhat later, the migrants returned,

bringing new species with them. Why did the near extinction and migrations

occur?

Another task for the Glomar Challenger

’

s scientists was to try to determine

the origin of the domelike masses buried deep beneath the Mediterranean

seafloor. These structures had been detected years earlier by echo-sounding

instruments, but they had never been penetrated in the course of drilling. Were

they salt domes such as are common along the United States Gulf Coast, and if

so, why should there have been so much solid crystalline salt beneath the floor

of the Mediterranean?

With question such as these clearly before them, the scientists aboard the

Glomar Challenger processed to the Mediterranean to search for the answers. On

August 23, 1970, they recovered a sample. The sample consisted of pebbles of

hardened sediment that had once been soft, deep-sea mud, as well as granules of