I’m trying to figure out when the boat was invented and when one could go for say, 50 miles over open water.
Well, Taiwan yield remains thought to date to about 50,000 years ago.
But the invention of the boat is likely much older than that. The main advantage of the boat is not that it enables you to sail off over the horizon and by chance discover an island that you had no idea was there; it’s that it enables you to travel up and down rivers, and along coasts, much faster, and with much greater loads, than would be possible by walking along the riverbank or the shoreline.
There were settlements around what is now the UAE 125,000 years ago. While it’s theoretically possible to walk there from the Great Rift Valley, it’s perhaps unlikely that that’s what happened.
According to this article, homo erectus was using boats and navigating open waters in Flores (in Indonesia) more than 800,000 years ago.
While the island was certainly colonized by crossing open water, according to the link the largest gap during times of lowered sea level was only 11.4 miles. It’s possible that humans may not have had boats that were ordinarily capable of crossing open water, but instead could have been using logs or rafts near the coast and were blown there inadvertently rather than getting there deliberately.
The island-hopping that populated Australi is estimated to have happened about 50,000 years ago; this included some serious crossings over the horizon, out of sight of land, so probably pretty advanced watercraft for the day.
Wikipedia says some experts think earliest Australian inhabitation was 125,000 years ago.
As soon as people discovered water, they no doubt discovered that any fool could bundle together some natural material into a flotation device, even to cross small streams. Thus, the boat would have been “invented” long before the ocean was ever even seen.
The first person that was drowning and grabbed onto a floating log that was passing by probably figured it out pretty quickly that this was a neat way to get to the other side.
And since such a boat - in the form of a crude raft - could have allowed humans to do one-way crossing of even reasonably large distances (e.g. the Torres Straight), we should perhaps be cautious of inferring nautical sophistication from evidence of early settlement.
While they weren’t humans, the current thinking is that Old World monkeys rafted over to the New World when South America and Africa were much closer together. Ironically, the first boat users were never able to rise to the occasion of building their own, while their Old World descendants went on to great success.
True, but they were probably the size of marmosets, and so didn’t need as big a “raft.”