The tiny skeletal hand jutted from the sand as if beckoning the living to the long dead.

For thousands of years, it had waved unheeded in the most desolate section of the Sahara, surrounded by the bones of hippos, giraffes and other creatures typically found in the jungle.

A chance discovery by a team of American scientists has led to the unearthing of a Stone Age cemetery that is providing the first glimpses of what life was like during the still-mysterious period when monsoons brought rain to the desert and created the "green Sahara."

The more than 200 graves that have been explored so far indicate that, beginning 10,000 years ago, two different populations lived on the shores of a massive lake, separated by a 1,000-year period during which the lake dried up.

Among the scientists' most surprising discoveries has been a poignant burial tableau of a mother and two children with fingers intertwined, a find that is putting a surprisingly human face on the little-known people who enjoyed a brief visit to Eden in what is normally one of the most forbidding places on Earth.

The first to settle the area was a group of tall, powerfully built hunters, gatherers and fishermen called the Kiffian, University of Chicago paleontologist Paul Sereno said at a news conference today.

The group who followed the Kiffian was a physically smaller band of pastoralists called the Tenerian, who relied on fishing and hunting but also herded cattle, he said.

"They've managed to find these people," said archaeologist Anne Haour of the University of East Anglia in Great Britain, who was not involved in the research. "We've always suspected something was going on, but this is the first time it has been properly documented."

In addition to the graves, researchers found a massive collection of the remains of meals, tools, pots and other artifacts – the detritus of everyday life.

"This is a real find … for a time period that is not very well documented in that part of the world," said archaeologist Kathy Schick of Indiana University's Stone Age Institute. "It's just a gold mine of information."

The new findings were published today in the online journal PLoS One and in the September issue of National Geographic magazine.

The Sahara has been a desert for untold millenniums. But about 12,000 years ago, a faint wobble in the Earth's orbit and some other factors caused Africa's seasonal monsoons to shift slightly north, bringing rains to the Sahara and greening it from Egypt in the east to Mauritania in the west.

About 8,000 years ago, the rains retreated, leaving the region arid once again and causing it to be abandoned. A thousand years later, the rains returned for two more millenniums, before permanently retreating.

The newly discovered site, called Gobero after the Tuareg name for the area, lies deep within Niger's Ténéré Desert, a large region within the still larger Sahara. The site lay unobserved and untouched because it was literally "in the middle of nowhere," Sereno said. "There is absolutely no reason for anyone to go there."

Sereno had a reason, of course, a nearby table of 110-million-year-old sandstone "that has more dinosaurs in it of high quality than any other rock in the continent of Africa."

In 2000, Sereno and a small group of colleagues were on one of their periodic "forays" in which they would load up a Land Rover and travel as far from their main site as they could in one day, looking for new dinosaur bones.

"We were at the end of our rope," Sereno said, nearly out of water and ready to turn around, when he spotted a stone formation sticking up in the distance and decided to go just a little farther.

When they got there, they found animal bones lying scattered on the surface, exposed by the weather. Photographer Mike Hettwer wandered off to a trio of small dunes, then rushed excitedly back to the group.

"I found some bones," he told them. "But they're not dinosaurs. They're human."