I read a comment on a thread in a different subreddit saying that humans have been seafaring for 100,000 years. That sounds a little ludicrous to me. Do we have any idea how long humans have been using boats to travel on oceans?
/r/askscience would be a good place to crosspost this.
Humans traveled to Australia around 50,000 years ago. That's incontrovertible evidence that humans had seafaring boats by at least that time.
In 2010, human artifacts were discovered on Crete and dated to around 130,000 BC, which really pushes back the launch date on seafaring. Despite years of research, however, there is almost no other evidence of seafaring in the Mediterranean before about 15,000 BCE. Link and link about that.
Homo erectus reached Flores Island by 800,000 years ago. Flores has never been closer than about 20 km from the Asian mainland implying an unsuspected degree of familiarity with the water on the part of Homo erectus (and maybe leading one to the conclusion boats aren't all that hard?)
Source: Morwood, M. et al. 1998. “Fission-track ages of stone tools and fossils on the east Indonesian island of Flores.” Nature 392: 173-176