Two thousand years ago, fishermen in the Aegean Sea off the island of Crete used huge stone tanks at the shoreline to keep their catch alive until they could take it to market.
The tanks had grates that kept the fish inside while the tides washed through, cleaning out stagnant water. The tanks are still there - more than 6 feet beneath the ocean's surface. But how did they get lower than the present sea level?Michael E. Lewis, associate professor of geology at Brigham Young University, and colleagues say a land bridge once connected an island 520 miles off the shore of Crete with mainland Crete.
His poster display on the subject was one of the highlights of the Geological Society of America convention held this week in the Salt Palace. About 4,000 geologists from across the country attended the sessions.
He said the archaeologist who has a permit to dig in the vicinity - an expert from the University of North Carolina - asked him if he and his team could find any physical and cultural evidence of a connection between an island off the northeastern coast of Crete and mainland Crete.
If the island was connected to the mainland at one time, "the idea is that . . . it would form a much better harbor, and that would have created a much better site for this village," Lewis said.
At the time of his field work, the summer of 1994, Lewis was with the University of North Carolina at Goldsboro, but he has been at BYU for the past year.
The island is where the town of Mochlos stood during the Bronze Age 5,000 years ago. Since then the town has shifted onto the nearby section of Crete itself. (Both Crete and the small outcrop are islands; Crete is far larger.)
"We were able to identify two sets of faults that placed the island in a down-dropped basin," he said.
He compared the island's earthquake faults with Salt Lake Valley, which is between the Wasatch Fault that runs through Salt Lake City and the Oquirrh Fault to the west.
The team mapped the contours of the land in detail, including finding exact depths of sections between the island and Crete. They located house walls the Minoans had built thousands of years ago. The walls were cut off at the present shoreline, but in those days they must have been back from the sea.
"We also found cultural evidence in the form of rock tanks carved into the surf zone," he said. "The water would slosh into the tank and slosh out." The tanks date to the times of the ancient Greeks and Romans.
Knowing how the tanks worked, Lewis realized at once they had to be the shore.
The researchers used computers to re-create the ancient shoreline, based on the assumption that the tanks were on the beach. The computer model exposed "a land connection between the island and mainland Crete," he said.
In other words, the earlier town of Mochlos was not on a separate small island at all but on Crete itself. Dry land extended between Crete and what is now the little island. The land bridge was substantial and rocky, rather than some transient sand spit.
In that earlier setting, Mochlos stood on a headland adjacent to a deep harbor, which made it an important trading and manufacturing center during the Bronze Age.
What happened to the sea level since then is not that the general ocean level rose dramatically, Lewis said, but that the island sank. In stages, deeper and deeper water filled in between it and Crete.
"An earthquake came along every now and then, and it would drop more," he said of the land between the faults' zones. "These Minoans occupied this site 5,000 years ago, and there's been a tremendous number of earthquakes in the 5,000 years."
Before the land sank, Mochlos must have had an excellent harbor. It could have been valuable to the whole Minoan civilization. "Rather than being just an obscure fishing spot, it was probably an important village, with trade links as far away as Egypt," Lewis said.