When and how did the first Humans arrive in the New World?

[desert]

I saw a documentary about this that posited a human presence in the Americas as long ago as 40,000 B.C., and presented evidence of human presence from 15,000+ years ago(footprints, tools) around the continents.

The documentary's theory was that people from Asia, Australia, and Europe basically sailed to the Americas on rafts and crude boats after 40000 or 30000 BC, and as evidence showed that the while some skulls of Americans 10000 years ago are similar to those of 1000 years ago, others are radically different (narrower, other skull stuff). So there were once multiple peoples dwelling in the Americas, but they all died out or were assimilated by a single one whose descendants we see today.

Then again, we all know how reliable these documentaries can be...

[Megas Methuselah]

That sounds like a pretty interesting documentry to watch, though.

[Fisherking]

I hope it is okay that I took this from the older Origin of Modern Humans thread:

It is not my intention to derail this topic but I read once in a scientific magazine that the first Americans were Australians.
A bit flippant, but they found sculls that were identical to Australian aborigine sculls.
I searched the Internet and found this article:

http://news.bbc.co.uk/1/hi/sci/tech/430944.stm

I had seen this article before but Sigurd had it cited so he deserves credit.

Some of this may also be linked to the major extension event of some 12500 years ago, along with most of the mega fauna.

When we think of human extension events we my want to look more closely at environmental conditions and event than just saying that other humans wiped them out. Man may be an efficient killer but he is also an efficient breeder and not too picky about who he breeds with. There should be evidence somewhere in the genitic record of even enemy groups.