During the peak of the last ice age, northeast Asia (Siberia) and Alaska were connected by a broad land mass called the Bering Land Bridge. This land bridge existed because so much of Earth’s water was frozen in the great ice sheets that sea levels were over 100 meters lower than they are today. Between 25,000 and 10,000 years ago, Siberia, the Bering Land Bridge, and Alaska shared many environmental characteristics. These included a common mammalian fauna of large mammals, a common flora composed of broad grasslands as well as wind-swept dunes and tundra, and a common climate with cold, dry winters and somewhat warmer summers. The recognition that many aspects of the modern flora and fauna were present on both sides of the Bering Sea as remnants of the ice-age landscape led to this region being named Beringia.

It is through Beringia that small groups of large mammal hunters, slowly expanding their hunting territories, eventually colonized North and South America. On this archaeologists generally agree, but that is where the agreement stops. One broad area of disagreement in expanding the peopling of the Americas is the domain of paleoecologists, but it is critical to understanding human history: what was Beringia like?

The Beringian landscape was very different from what it is today. Broad, windswept valleys, glaciated mountains, sparse vegetation, and less moisture created a rather forbidding land mass. This land mass supported herds of now-extinct species of mammoth, bison, and horse and somewhat modern versions of caribou, mush ox, elk, and saiga antelope. These grazers supported in turn a number of impressive carnivores, including the giant short-faced bear, the saber-tooth cat, and a large species of lion.

The presence of mammal species that require grassland vegetation has led Arctic biologist Dale Guthrie to argue that while cold and dry, there must have been broad areas of dense vegetation to support herds of mammoth, horse, and bison. Further, nearly all of the ice-age fauna had teeth that indicate an adaptation to grasses and sedges; they could not have been supported by a modern flora of mosses and lichens. Guthrie has also demonstrated that the landscape must have been subject to intense and continuous winds, especially in winter. He makes this argument based on the anatomy of horse and bison, which do not have the ability to search for food through deep snow cover. They need landscapes with strong winds that remove the winter snows, exposing the dry grasses beneath. Guthrie applied the term “mammoth steppe” to characterize this landscape.

In contrast, Paul Colinvaux has offered a counterargument based on the analysis of pollen in lake sediments dating to the last ice age. He found that the amount of pollen recovered in these sediments is so low that the Beringian landscape during the peak of the last glaciation was more likely to have been what he termed a “polar desert,” with little or only sparse vegetation. In no way was it possible that this region could have supported large herds of mammals and thus, human hunters. Guthrie has argued against this view by pointing out that radiocarbon analysis of mammoth, horse, and bison bones from Beringian deposits revealed that the bones date to the period of most intense glaciation.

The argument seemed to be at a standstill until a number of recent studies resulted in a spectacular suite of new finds. The first was the discovery of a 1,000-square-kilometer preserved patch of Beringian vegetation dating to just over 17,000 years ago—the peak of the last ice age. The plants were preserved under a thick ash fall from a volcanic eruption. Investigations of the plants found grasses, sedges, mosses, and many other varieties in a nearly continuous cover, as was predicted by Guthrie. But this vegetation had a thin root mat with no soil formation, demonstrating that there was little long-term stability in plant cover, a finding supporting some of the arguments of Colinvaux. A mixture of continuous but thin vegetation supporting herds of large mammals is one that seems plausible and realistic with the available data.

在上个冰河世纪的高峰时期，亚洲东北部（西伯利亚）和阿拉斯加被称为白令陆桥的广大陆块相连。这片陆地桥之所以存在，是因为冰川贮藏了地球上大部分的水，海平面比现在低了100多米。 在二万五千年至一万年前，西伯利亚，白令陆桥和阿拉斯加有着许多共同的环境特征。这其中包括常见的大型哺乳动物，由广阔的草原，风沙丘和苔原组成的常见植物群，气候为寒冷干燥的冬季和较为舒适的夏季。人们认识到，在白令海的两侧呈现出现代动植物的许多方面特征，作为冰河时代景观的遗迹，导致该地区被命名为白令海峡。 通过白令海峡，一群大型哺乳动物的捕猎者慢慢地扩大了他们的狩猎领地，最终在南美和北美殖民。考古学家们大体上同意这一点，但这就是协定的终止之处。这个考古学家普遍认同，但那是协议停止的地方。 在扩大美洲人口方面有一个广泛的分歧，那就是古生态学家的研究领域，但理解人类历史至关重要：白令海峡是什么样的？ 白令海峡的风景与今天的风景完全不同。广阔的海风吹拂的山谷，冰川的山脉，稀疏的植被和较少的水分，形成了一个相当令人生畏的土地。这块土地上有现已灭绝的猛犸象、野牛和马，以及一些现代版的驯鹿、麋牛麋鹿和赛加羚羊。 这些食草动物反过来支撑了一些令人印象深刻的食肉动物，包括巨型短面熊，剑齿猫和一大群狮子。 由于哺乳动物的出现需要草原植被，使得北极生物学家戴尔古斯里认为，虽然天气寒冷干燥，但一定要有广阔茂密的植被，以支撑猛犸象，马和野牛群的生活，此外，几乎所有的冰河时期动物都有牙齿，这表明它们适应了苔藓及地衣;但是现代植物苔藓和地衣不能支撑它们的生活，格思里还证明，这一景观一定经受了强烈而持续的风的影响，特别是在冬季。 他根据马和野牛的解剖来论证这一论点，因为它们无法通过深雪覆盖搜寻食物。他们需要用强风来除去冬天的雪，露出下面的干草。格思里使用“猛犸草原”这个词来描述这个景观。 相比之下，Paul Colinvaux基于对上一个冰河时期湖泊沉积物中花粉的分析提出了反驳。 他发现在这些沉积物中发现的花粉数量非常少，以至于在末次冰期的高峰时期，白令海峡风景更可能是他所谓的“极地沙漠”，那里几乎没有植被。这个地区绝不可能支撑大量的哺乳动物的生活，人类猎人也不可能。格思里反驳了这一观点，指出从白令海峡的沉积物中对猛犸象、马和野牛骨骼的分析显示，这些骨骼的年代是最紧张的冰川时期。 这个论点似乎处于停滞状态，直到最近的一些研究成果出现了一系列新的发现。 首先是发现了一个1000平方公里的白令植被的保存区，它的历史可追溯到1.7万年前，也就是上个冰河时期的顶峰时期。这些植物是在火山喷发后的厚灰中保存下来的。正如格瑟里所预测的那样，对这些植物的调查发现草，莎草，苔藓和许多其他品种几乎是连续覆盖。 但是这种植被有一个没有土壤形成的薄根垫，这表明植物的覆盖几乎不能长期稳定，这一发现支持了Colinvaux的一些论点。 一种连续稀疏的植物混合物能够支撑大型哺乳动物群存活，在现有的数据中似乎是可信的和现实的。