There was a study published in Nature last year  that concluded that it took hundreds of years after the ice sheets receded and the route become passable before plants became established, and then later animals, to make it possible to survive off the land during such a trip.
We know that the Clovis culture was established before then, so if they or earlier people came by the land route then they must have brought their supplies with them.
That was before the invention of the wheel, so if they brought all their supplies with them for the journey it wasn't on wagons or carts. They only animals they might have had to help carry things were dogs, because no other animals were domesticated at that point.
So we're looking at carrying everything they need for the trip on their own backs or on crude sleds, possibly with the aid of dogs (and if they are bringing dogs, they have to bring all the food for the dogs, too).
This just seems to me to be too farfetched.
Now compare to coming by boats. With boats it is easy to bring plenty of cargo. Whatever food they bring with them can be supplemented with fish and other seafood they can catch on the way. Maybe they can even live entirely off seafood.
 I haven't seen the study itself freely online, but here's an article that goes into detail about it: http://www.history.com/news/new-study-refutes-theory-of-how-...
To be clear this refers to the fusion of the Laurentide (Canadian) and Cordilleran (Pacific NW) ice sheets but the caveats are this doesn't preclude travel into parts of Alaska and it's also possible there was some travel before the sheets were fused.
> brought all their supplies with them
Maybe they didn't have a lot of supplies? I mean people migrated all over Siberia and presumably many/most of them did so on foot.
> they have to bring all the food for the dogs
The traditional view was that they were following the food source. And presumably they kept the dogs around in the first place because (among other reasons) they help hunt and are also a food source.
> Whatever food they bring with them can be supplemented with fish and other seafood they can catch on the way. Maybe they can even live entirely off seafood.
This logic works with any food source though.
I genuinely don't know, but that seems surprising.
Regarding boats capable of crossing the ocean: Australia was settled 40,000 years ago, presumably by settlers who arrived by boat.
While they are obviously the end point of a technological development, Polynesian outrigger sailing canoes are both extremely efficient (some evidence points to them being the first craft to be capable of exceeding hull speed) and scalable. They're also a Stone Age technology
The Morris West book "The Navigator" is also interesting in this connection (though there is only a bit of discussion of the navigation topic in the book, it is not the main focus), and the book is a good read apart from that, both entertaining and for topics like human dynamics when on a voyage as well as when stranded on an island for a long period.
Update: Added link to his Wikipedia page:
I got a ride on a catamaran once, in South India, when our final year class (high school) was there at a beach on a picnic. Asked the fishermen to let me hop on, and they did. I was sitting in the front, astride the log, with my legs in the water almost up to waist level. We went out to sea for a kilometer or two at least, then came back after a while. Good fun.
It was something like this, but narrower in the front:
where it says that a British sailor created a reconstruction of that type of ship and sailed in it from Indonesia via Madagascar, and then around the Cape of Good Hope to Ghana. Reminded me of Thor Heyerdahl's Kon-Tiki voyage :), which I had read about in a National Geographic article about the voyage some years ago.
In all fairness, such evidence would be hard to find because at the time sea-level was 400 feet lower than it is today. It is likely that the best archaeological sites are now underwater. The article of course mentions this. In fact, the article mentions one location in British Columbia (Quadra island) where post-glacial rebound was so great that near-sea-level sites during the last ice-age are still above sea-level today. But that investigation is relatively recent.
Although in practice, actually finding them is hard. Note there are sites like this in Europe, too.
And we have consensus on this?
> Archaeology has now revealed that the wheel wasn’t invented until the 4th millennium BC – which puts it thousands of years after the first cities were built and after the invention of metallurgy, and its importance in determining the intelligence of a race is no longer rational.
Boats solve a more basic problem. No-one needs wheels - there are other means of transportation available.
Also, the above article points out that Mesoamericans seem to have independently invented the wheel, and even made wheeled toys.
You could say something similar about the Polynesians, although they came later
Ah, this might turn in to a "What has the wheel ever done for us" sketch after the style of Monty Python.
(Try making a decent sized wheel out of a plank - it'll shatter along the grain. Getting a snug 90 degree hole for the axle isn't trivial, either, and without that the wheel will wobble so badly it'll be largely useless.)
A solid one is easier to make, but will be very heavy and have severe durability problems.
You also have never seen a machine in your life. You have nothing at all to guide or inspire you.
Wheels might have been invented and then abandoned and forgotten multiple times, because they were too hard to make and not that useful.
From a piece of wood hanging on notched or Y shaped branches on which to hang meat for smoking/cooking to a spit to a pulley doesn't seem to far?
A simple barrow is a couple of sticks with a pulley. Though the utility over a simple dragged carrier is not much.
"Circumstantial evidence, such as the early settlement of Australia over 40,000 years ago, findings in Crete dated 130,000 years ago, and findings in Flores dated to 900,000 years ago, suggest that boats have been used since prehistoric times. ... The oldest recovered boat in the world is the Pesse canoe, a dugout made from the hollowed tree trunk of a Pinus sylvestris and constructed somewhere between 8200 and 7600 BC" - https://en.wikipedia.org/wiki/Boat
"The invention of the wheel falls into the late Neolithic, ... 4500–3300 BCE: Chalcolithic, invention of the potter's wheel; earliest wooden wheels (disks with a hole for the axle); earliest wheeled vehicles, domestication of the horse" - https://en.wikipedia.org/wiki/Wheel
Inventing a canoe or a raft is of course much easier than inventing the wheel, you just go on the shore of a river or at the seaside and you will find trunks or wooden pieces floating.
From that to have a boat capable of crossing an ocean there is a long way.
Also, the numbers would be important.
I would presume that leaving from a shore in search of another one (and knowing nothing on where that could be) would have been an extremely dangerous attempt, most probably taken by a handful of young males (hunters/gatherers, etc.) in the hypothesis that society was a male dominated one, possibly in very small/basic boats.
Then they would need to go back home, and then return bringing with them their spouses and presumably children.
Think of a future archaelogist in - say - 5,000 years time (after humanity and civilization collapsed) finding ONLY a hut with a few (perfectly conserved) surf tables and windsurfs.
From that finding to believe that windsurfs could be used for cross-sea or cross-ocean migrations there is somehow a large gap.
I don't understand what the point of your comment is.
The first humans in the Americas didn't need to cross an ocean. They needed to follow the shoreline. Even now the Bering Straight is only 90 km across. As the article points out, during the Ice Age, when the sea was lower, it was all land, known as Beringia. There was no "cross-sea or cross-ocean migration".
We know humans 60,000+ years ago could cross the Weber Line, which was also at least some 90 km wide, to get from Sunda to Sahul (which includes modern Australia). This migration to the Americas would have been easier than that.
Regarding male dominated society, hunter-gatherer cultures tend to be egalitarian. https://en.wikipedia.org/wiki/Hunter-gatherer#Social_and_eco... . One hypothesis is that male dominated culture is a result of agriculture, and specifically the horse and plow. http://voxeu.org/article/modern-gender-roles-and-ancient-far... . However, I this is a topic I know little about. I bring it up as an example of why I am confused about the point of your comment and where you're coming from.
I was actually supporting the idea that inventing the boat is (should be) easier than inventing the wheel BUT that between inventing the boat and actually being able of building big enough boats AND boats being able to cross large stretches of water AND actually using them to "migrate" a population there are some leaps.
The grandparent comment was not about "boats", was about "boats that can travel across the ocean" and the article was
about the hypothesis of a migration by boat.
They're easily big enough to cross the Bering Strait (in fact, before the Cold War, they did it routinely) and can be constructed completely from local materials (sea mammal hide covering, whale bones and driftwood for ribs -- modern umiaks often use metal fasteners, but traditional ones didn't).
Alaska Natives still prefer them for some tasks (e.g., whale hunting).
That requires neither a big boat nor one which can cross large stretches of water. That's why I didn't understand where your comment fit into the topic.
I mean, there are photographs from that era.
Yet it was how the Polynesians settled the Pacific.
Or they could simply have claimed, most archeologists believe the first ancient people to arrive in the lower 48, arrived by boat.
The context is they theoretically traveled along the littoral in boats vs some inland pathway on foot.
Early Americans apparently knew how to take full advantage of its abundant resources. At Monte Verde, once 90 kilometers from the coast, archaeologist Tom Dillehay of Vanderbilt University in Nashville found nine species of edible and medicinal seaweed dated to about 14,000 years ago.
"American" also describes the citizens of that one state with the word "America" in the name, which sometimes leads to ambiguity, but not here.