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Colonizing the Americas via the Northwest Coast

It has long been accepted that the Americas were colonized by a migration of peoples from Asia, slowly traveling across a land bridge called Beringia (now the Bering Strait between northeastern Asia and Alaska) during the last Ice Age. The first water craft theory about the migration was that around 11,000-12,000 years ago there was an ice-free corridor stretching from eastern Beringia to the areas of North America south of the great northern glaciers. It was the midcontinental corridor between two massive ice sheets-the Laurentide to the west-that enabled the southward migration. But belief in this ice-free corridor began to crumble when paleoecologist Glen MacDonald demonstrated that some of the most important radiocarbon dates used to support the existence of an ice-free corridor were incorrect. He persuasively argued that such an ice-free corridor did not exist until much later, when the continental ice began its final retreat.

Support is growing for the alternative theory that people using watercraft, possibly skin boats, moved southward from Beringia along the Gulf of Alaska and then southward along the Northwest Coast of North America possibly as early as 16,000 years ago. This route would have enabled humans to enter southern areas of the Americans prior to the melting of the continental glaciers. Until the early 1970s, most archaeologists did not consider the coast a possible migration route into the Americans because geologists originally believed that during the last Ice Age the entire Northwest Coast was covered by glacial ice. It had been assumed that the ice extended westward from the Alaskan/Canadian mountains to the very edge of the continental shelf, the flat, submerged part of the continent that extend into the ocean. This would have created a barrier of ice extending from the Alaska Peninsula, through the Gulf of Alaska and southward along the Northwest Coast of North America to what is today the state of Washington.

The most influential proponent of the coastal migration route has been Canadian archaeologist Knut Fladmark. He theorized that with the use of watercraft, people gradually colonized unglaciated refuges and areas along the continental shelf exposed by the lower sea level. Fladmark's hypothesis received additional support from the fact that the greatest diversity in Native American languages occurs along the west coast of the Americans, suggesting that this region has been settled the longest.

More recent geologic studies documented deglaciation and the existence of ice-free areas throughout major coastal areas of British Columbia, Canada, by 13,000 years ago. Research now indicates that sizable areas of southeastern Alaska along the inner continental shelf were not covered by ice toward the end of the last Ice Age. One study suggests that except for a 250-mile coastal area between southwestern British Columbia and Washington State, the Northwest Coast of North America was largely free of ice by approximately 16,000 years ago. Vast areas along the coast may have been deglaciated beginning around 16,000 years ago, possibly providing a coastal corridor for the movement of plants, animals, and humans sometime between 13,000 and 14,000 years ago.

The coastal hypothesis has gained increasing support in recent years because the remains of large land animals, such as caribou and brown bears, have been found in southeastern Alaska dating between 10,000 and 12,500 years ago. This is the time period in which most scientists formerly believed the area to be inhospitable for humans. It has been suggested that if the environment were capable of supporting breeding populations of bears, there would have been enough food resources to support humans. Fladmark and others believe that the first human colonization of America occurred by boat along the Northwest Coast during the very late Ice Age, possibly as early as 14,000 years ago. The most recent geologic evidence indicates that it may have been possible for people to colonize ice-free regions along the continental shelf that were still exposed by the lower sea level between 13,000 and 14,000 ago.

The coastal hypothesis suggests an economy based on marine mammal hunting, saltwater fishing gathering, and the use of watercraft. Because of the barrier of ice to the east, the Pacific Ocean to the west, and populated areas to the north, there may have been a greater impetus for people to move in a southerly direction

【正确答案】 B

【答案解析】

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从西海岸殖民美洲

这种观念被人们接受很长时间了：美洲被一群来自亚洲的移民殖民统治着，他们在上一个冰河时代缓慢的跨越了一个叫做白令的大陆桥（现在白令海峡位于东北亚和阿拉斯加之间）。关于这些迁徙的第一个水路理论表明，大概在 11000 到 12000 年前，有一个不冻的走廊，它从白令海峡东部延伸到北美（大北部冰河的南部），连在两个巨大冰床间的半大陆性走廊，向西的 Laurentide 使往南的迁移成为可能。但是当生态学者 Glen MacDonald 证明一些用来支持不冻走廊存在的重要放射性碳时间不正确时，对于不冻走廊的信念就被粉碎了。他令人信服的主张那样的不冻走廊直到很久以后才出现，那时大陆冰开始最后的消退。

另外一种理论得到越来越多的人的支持，它认为可能早在 16,000 年前，人们使用船只，也许是那种兽皮做的小船，从白令沿着阿拉斯加海湾，然后沿着北美的西北海岸前进。这条路线使人类可以在大陆冰河解冻之前进入美州南部地区。直到 20 世纪 70 年代早期，大部分考古学家都不认为海岸可能是进入美州的移民路线，因为地理学家一开始就坚信整个西北海岸在上个冰河时代是被冰覆盖的。人们猜测冰从阿拉斯加、加拿大山脉向西延伸到大陆架的边界，也就是大陆延伸到海洋中而被淹没的部分。这样就形成了一个由冰构成的，从阿拉斯加半岛，经过阿拉斯加海湾，向南沿着北美州西北海岸延伸至今天的华盛顿州的冰层。

海岸移民路线的最有影响力的支持者是加拿大考古学家 Knut Fladmark。他认为通过船只的使用，人们逐渐殖民到没有冰冻的地方以及沿着大陆架的、由于海平面较低而裸露出来的地区。Fladmark 的假设从一个事实那得到了更多的支持，因为美国本土语言的最大多样性出现在西海岸沿岸，这就表明这个地区是人类定居时间最早的。

更多最近的地质研究证明了 13000 年前在英属哥伦比亚、加拿大主要海岸地区无冰区域存在和结冰。现在研究表明，直到上个冰河时代末期，阿拉斯加东南、沿大陆架内的大部分地区并没有被冰层覆盖。一项研究表明，除了在英属哥伦比亚东南部和华盛顿州之间的 250 英里的海岸地区以外，北美的西北海岸在大概 16000 年之前都是没有冰的。沿海的辽阔地区的冰川在大约 16000 年前开始融化，这就为 13000 前到 14000 年前的某一段时间内植物、动物和人类的迁移提供了一个海岸走廊。

海岸走廊假设近些年得到了越来越多的支持，因为一些大型动物（比如北美驯鹿，棕熊）的遗迹出现在阿拉斯加东南部地区，其时间为 10000 年到 12500 年之前。之前大部分科学家认为此时此地不适合人类生存的。如果一种环境能满足熊的繁殖，那么它就有足够的食物来源来供应人类的生存。Fladmark 和其他科学家都认为人类第一次乘船沿着西北岸到达美洲发生在冰河时代的晚期，可能早达 14000 年以前。多数最新的地质资料表明：13000 年至 14000 年前，人们殖民因低海平面而裸露的大陆架沿岸的无冰区域是可能的。

海岸假设提出了一个以捕食海洋哺乳动物、搜捕咸水鱼类、使用船只为基础的自然经济。由于东部是冰障，西部是太平洋，北部是移民区，所以有一股强大的力量促使人们往南方迁移。