Question

What contributed the most to human migration more than ten thousand years ago?
Sturdy boats were invented.
Another Ice Age occurred.
A major volcano erupted in Africa.
A severe drought occurred.

Answer 1

I would say that the likely candidates are the first and the second option, the rest is not as likely to contribute to human migration.

Now, as far as I know, most Island-hopping happened actually in more primitive boats. Ice Age (that's my choice) allowed people to reach a whole new continent -America, by lowering sea level and freezing over Berin Strait - so I think this had the biggest influence!

Answer 2

The correct answer is that another Ice Age occured and contributed the most to human migration more than ten thousands years ago.

The Earth was going through an Ice Age phase more than ten thousands years ago and during that period as a result of the lower level of the seas along with the large ice masses, numerous land-bridges arised. Humans capitalized on those land bridges and used them to migrate to new territories.