Human ancestor may have taken to sea.

An evolutionary predecessor of modern humans known as Homo erectus apparently used some type of seaworthy craft to reach the Indonesian island of Flores at least 800,000 years ago, according to a new study.

Most researchers treat the settlement of Australia by H. sapiens between 40,000 and 60,000 years ago as the earliest instance of systematic sea travel.

"Even at times when the sea level was lowest, water crossings were necessary to reach Flores from Southeast Asia," write archaeologist Michael J. Morwood of the University of New England in Australia and his colleagues. "We conclude that H. erectus in this region was capable of repeated water crossings using [sea]craft."

Fission-track dating of volcanic ash grains provided the estimated ages of two sites on Flores, an island located east of Java and Bali, the scientists report in the March 12 Nature. This dating method relies on counting the microscopic damage tracks that accumulate as uranium atoms spontaneously undergo fission, or splitting.

One Flores site, called Mata Menge, yielded 14 stone tools in a 1994 excavation and several more last year, Morwood's group reports. The artifacts lie in sediment that contains the bones of several ancient animals also found in Southeast Asia, such as large, elephant-like creatures, crocodiles, and giant rats. The Mata Menge finds date to between 880,000 and 800,000 years ago.

The second site, Tangi Talo, contains animal remains but no stone artifacts. The site dates to approximately 900,000 years ago.

The new evidence supports a couple of previous reports of stone artifacts on Flores attributed to H. erectus, discoveries that have been generally dismissed or ignored, the scientists say. The limited array of animals found in the ancient soil indicates that Flores was a relatively isolated island at that time, they theorize. A sea crossing from the mainland would have covered at least 11 miles, in their view.

H. erectus may also have made shorter ocean trips from Java. Some investigators place this hominid on Java as early its 1.8 million years ago (SN: 3/5/94, p. 150).

Other researchers now suspect that H. erectus crossed small stretches of the Mediterranean Sea beginning around 1 million years ago (SN: 1/4/97, p. 12).

"This is a very provocative new report," remarks anthropologist F. Clark Howell of the University of California, Berkeley. Dating and excavation techniques appear thorough, he notes. Drawings of the stone finds are "highly suggestive" of genuine artifacts, says Howell, though he cannot vouch for their authenticity with absolute certainty.

The existence of H. erectus in Indonesia around 800,000 years ago is not surprising, remarks archaeologist Stanley H. Ambrose of the University of Illinois in Urbana. Earth's crust has frequently shifted in this region, he notes, raising the possibility that a land bridge once connected the Southeast Asian mainland to Flores.