Who Has the Burden of Proof?

[robvalue]

In your example, both sides are making claims, so I say both have the burden of proof for their individual claims. A sceptical, uninformed third party would believe neither claim until evidence was put forward.

As usual, I'd start with definitions and get both sides to say exactly what they think a "continent" is. It may be that they are both right, given the definition they are each using.