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I am making a game folowing the development of civilizations on an alien planet, however as i am almost done with the geography of this planet, i have come to realize that my continents which are seperated by oceans are quite far apart and i am starting to worry that early intelligent life would not be able to spread to all continents of this planet (after all humans took a while to spread to the Americas).

My question is therefore: how large could oceans be that humans could (for simplicities sake I will let my aliens be very close to humans) realistically migrate across with only technology comparable to what humans on earth used to settle the islands of the pacific. Would it be easier or more difficult for humans to migrate across water in warmer regions of the planet than colder and how close would the islands in the oceans have to be? (Assuming that all conditions, including weather and climate, is the same as on earth.)

edit: to specify slightly, i did make some calculations on the distances between my continents at the specific places I imagine that migrations would follow and they mostly fall somewhere between 2700 km and 6750 km, which might not be that far from earth after all, but as one answer points out, I do not know what effect the ocean currents would have.

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First off, humans in paleolithic times successfully colonized Australia long before agriculture and such. Even while island-hopping across Indonesia when the ocean level as 120m lower than today, that feat involved watercraft crossings of tens (possibly hundreds) of kilometers, and definitely involved crossings too far to see across. Its hard to say how far the longest crossing was, since we don't even know for sure how low the sea levels were, but I'm estimating the longest gap is Borneo to Sulawesi, at about 110km.

From the Mediterranean in Neolithic times, Cyprus, Crete, Malta, and other islands were settled 12000-10000 BC. Those crossings were a minimum of 75km of deep water and are more likely to have been done on purpose in a purpose build watercraft, as opposed to on accident or using a pile of logs.

Finally, by the time of the centuries AD, there were no longer any limits to how far they could travel by ocean. The Polynesians settled Easter Island ~900AD from either the Gambier or Marquesas, either 2600 or 3200 km away. Also the Polynesians traded sweet potatoes (at least) with South Americans sometime before European contact, another open ocean trek of 3000km or so.

The record holders are probably the Austronesians from Sumatra or Java who settled Madagascar in around 250AD. They may have taken outrigger canoes across the southeast trades in the South Indian ocean, meaning they had to do about 5500 km of direct ocean sailing to get to Madagascar; 5000km if they stopped at Maurutius or Reunion along the way...although there is no evidence of that.

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Hello and welcome to world building. Nice first question.

How far apart is "quite far"? I'll assume it's roughly the same distances that we have on earth today.

Sadly, i can only partially answer your question. I cannot give you a maximum size for an ocean that could be crossed. But i can quite positively tell you that all the pacific ocean was successfully crossed with the technology you describe. Please refer to the Kon Tiki Expedition. A norwegian researcher built a raft from basal wood, all with historical crafts and equipment, and crossed the pacific on a very long and historically famous journey. He travelled 101 days, and did roughly 7000 kilometers.

Later expeditions by other researchers managed to do even longer journeys of 10.000km and more.

Even though, one would expect a lot of these expeditions to fail, and especially since you wouldn't originally KNOW that there is land on the other side, it would be a daunting and dangerous task. Also you require correct currents to cover the necessary distance in a survivable time. But i think on most earth-sized planets, most oceans could be crossed by your aliens.

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