Where does the people come from?

According to wikipedia, the history is divided into four parts:
Pre-Columibian Era
European Colonization
Independence
Recent History

所以，可以问的第一个问题是：最初的人是哪儿来的？
下面是wikipedia的一段说明：

South America is thought to have been first inhabited by people crossing the Bering Land Bridge, now the Bering strait, though there are also suggestions of migration across the southern Pacific Ocean. Over the course of millennia, people spread to all parts of the continent. By the first millennium CE, South America’s vast rainforests, mountains, plains, mountain and coasts were the home of tens of millions of people.

CE也就是AD，是公元的非宗教性的名称：Common Era。AD是拉丁文， anno Domini (AD) ，有宗教色彩，表示“主诞生的那一年”。（当然这段与历史无关：））

也就是说普遍的观点是：南美洲的人都是外来人口。有人认为他们是通过一个叫做Bering Land Bridge的land bridge进入南美洲；有人认为他们是通过southern Pacific Ocean游过来的？坐船过来的？

这个很有意思。What makes them think so? How do they verify this?（这可以是个问题，不过作为历史了解性的Blog太过细节了）

关于Bering Land Bridge：

The Bering land bridge, also known as Beringia, was a land bridge roughly 1600 km (1000 miles) north to south at its greatest extent, which joined present-day Alaska and eastern Siberia at various times during the ice ages.

关于land bridge：

Land bridge is essentially a historical term; it refers to dry land exposed during periods of low sea level (see regression), connecting what are now separate continents or islands.

关于Ice ages:

...the last ice age ended about 10,000 years ago.

关于人类诞生的时间：

The view most widely accepted by the anthropological community is that the human species originated in the African savanna between 100 and 200 thousand years BCE, colonised the rest of the Old World and Oceania by 40,000 years BCE, and finally colonised the Americas by 10,000 years BCE.

所以人类诞生以后就在地球上走来走去，最后走过了亚洲，然后通过Beringia走到美洲。Sound reasonable.

准确地说是走到阿拉斯加，然后通过北美洲走到南美洲。是不是这样呢？我们假设板块运动学说是正确的，10000BCE的时候大陆是什么样子的？如果那时候和现在差不多，估计应该是从北美洲跑到南美洲了。