每日一文20180604

最新发现推测，最早来到美洲大陆的人类可能是沿着海岸线进入美洲内陆的，质疑了以前的沿着“无冰走廊”进入的说法。但是，目前，在新提出的海岸线上还没有发现人类骨骼和人工制品。不过，科学家对17000多年前的海豹骨骼化石进行碳放射性研究发现，在冰川后退后，露出海平面的沿海一带（黄线）已经成为动物的栖息地。

The first Americans could have taken a coastal route into the New World

Glacial retreat had cleared a path along Alaska’s shores by 17,000 years ago

BY BRUCE BOWER 2:00PM, MAY 30, 2018

DEICED PASSAGE  Rocks on an Alaskan island display smooth surfaces covered by cracks created when ice once moved over them. Alia Lesnek (shown) and colleagues have determined that ice on this and three nearby islands retreated about 17,000 years ago, just before ancient humans colonized the Americas.

Ancient colonizers of the Americas could have traveled down Alaska’s Pacific coast in canoes or other sea vessels around 17,000 years ago, a new study finds.

At that time, toward the end of the last ice age, glaciers冰川 had just receded后退 from a cluster of southern Alaskan islands, say geologist Alia Lesnek of the University at Buffalo in New York and colleagues. Life-supporting habitats appeared soon after the ice melted, the scientists report May 30 in Science Advances.

COASTING DOWN Analyses of rocks on four islands off southeastern Alaska’s coast (black rectangle shows location of the studied islands) indicate that humans could have reached the Americas around 17,000 years ago by taking a coastal route (orange) rather than going inland to an ice-free corridor (red).

The study is the latest to  weigh in发表又分量的意见 on the debate over how humans spread into the New World after arriving from Asia and reaching as far as Florida and South America by 14,500 years ago (SN: 6/11/16, p. 8; SN: 12/26/15, p. 10). Previous work has hinted暗示 that an inland内陆, ice-free corridor from Alaska through what’s now British Columbia and into the United States may not have contained enough vegetation and wildlife to enable human travel before around 12,600 years ago (SN Online: 8/10/16). New geologic evidence supports the idea of a coastal route, though Lesnek’s team found no human bones or artifacts on the islands.

Measures of chemicals that accumulate in rock due to cosmic radiation once glaciers retreat provided age estimates for when four Alaskan islands lost their ice coat. An open pathway for coastal travelers probably existed along the entire southeastern Alaskan coast roughly 17,000 years ago, the scientists say. Radiocarbon dates for a ringed seal’s remains found on a southern Alaskan island indicate that the seal lived about 17,000 years ago, suggesting the area became habitable soon after glaciers left.

Citations

A.J. Lesnek et al. Deglaciation of the Pacific coastal corridor directly preceded the human colonization of the Americas. Science Advances. Published online May 30, 2018. doi:10.1126/sciadv.aar5040.

Words：

glaciers冰川

reced后退

weigh in发表又分量的意见

hint暗示

inland内陆