Early Native Americans spent millenia living on the Bering Land Bridge now buried under water before they appeared in Alaska and the rest of the North America, researchers said Friday.

The finding provides answers to a long-running mystery about where the people who first set foot on the New World survived the last Ice Age after splitting from their Asian relatives 25,000 years ago.

"This work fills in a 10,000-year missing link in the story of the peopling of the New World," said Scott Elias from the Department of Geography at Royal Holloway college in London.

Insect and plant fossils found in the ancient Bering Land Bridge's sediment cores revealed that hundreds or thousands of people likely called central Beringia home for 5,000 years or more.

The theory, known as the "Beringia Standstill," was first proposed in 1997 by two Latin American geneticists and refined a decade later by a team led by the University of Tartu in Estonia that sampled mitrochondrial DNA from more than 600 Native Americans.

Mutations in the DNA indicated that a group of the Native Americans' direct ancestors were likely isolated for at least several thousand years in the Bering Land Bridge area.

- Shrub key to life -

The land bridge is now buried about 50 to 60 meters (160-200 feet) under the waters of the Bering and Chukchi Seas.

But thousands of years ago, the strip of land and nearby areas were covered in shrub tundra typical of modern Arctic Alaska, including dwarf willow and birch shrubs, mosses and lichens.

"We believe that these ancestors survived on the shrub tundra of the Bering Land Bridge because this was the only region of the Arctic where any woody plants were growing," Elias said.

"They needed the wood for fuel to make camp fires in this bitterly cold region of the world."

Elias, whose study was published in the US journal Science, explained that the population likely used dwarf shrub wood to help start a fire, then placed large mammal bones on top whose inner fats would help keep the flames burning for hours during frigid Arctic winter nights.

Many archeologists now say early humans first migrated to the New World about 15,000 years ago after retreating glaciers provided a path into North America through coastal and interior routes, though the subject is still a matter of debate.

Elias and his colleagues also analyzed certain beetle species living in specific temperature zones, which indicated that temperatures were relatively mild as the last ice age peaked, around 27,000 to 20,000 years ago.

"From my view the genetics and paleoecology data come together nicely," said University of Colorado Boulder researcher John Hoffecker, lead author of the study appearing in Science.

Hoffecker said the prehistoric inhabitants of Beringia may have hunted successfully in the uninhabited steppe-tundra region to the east and west.

Drier conditions and more grass in those areas likely fed many grazing animals such as steppe bison, horse and mammoth.