Consider a world that is much larger than Earth, but has Earthlike conditions on the surface. (Including gravity = 1g, by some suitable unobtainium.) Clearly, the surface could be covered in a large number of small continents and oceans, but I'm also interested in the possibility of larger ones.
Consider, specifically, a continent a million miles wide, surrounded on all sides by an ocean a million miles wide. What would conditions be like in the interior of the continent?
An obvious first guess is that nearly all the area of the continent would be far from the ocean and therefore, lacking a source of water, would be bone-dry desert.
On the other hand, thinking about it a bit more, there would surely be some water even in the center of the continent, by the second law of thermodynamics. If every water molecule were removed from the interior and dumped into the ocean, this would be a low-entropy state; some water will spontaneously diffuse over the whole area, until a state of maximum entropy is reached. In other words, as you journey from the coast toward the interior, the quantity of water per square mile will decrease for the first few thousand miles, but eventually reach a nonzero floor and stay there. So the second guess is that even the center of the continent will not be absolutely dry.
Then again, even though there is a nonzero quantity of water per square mile, that doesn't necessarily mean liquid water. Third guess: maybe the amount will be small enough that the humidity never approaches one hundred percent, so it all stays as water vapor and there is never any liquid water.
But there is differential heating between night and day, and between rock formations with higher and lower albedo. Wind blows across land of different elevations. Chaotic fluid dynamics applies. There is, in short, still weather. Could the weather ever concentrate water vapor enough to produce occasional rain?
Does it matter if there are some lakes and small seas? Consider a sea one thousand miles wide, in the center of the continent. It seems unlikely that it will matter whether the elevation is equal to the ocean half a million miles away. Either way, the water seems likely to end up scattered in the form of vapor across the whole continent. But then, what distinguishes that case from a much larger sea? If there is a sea half a million miles wide within the continent, that seems obviously likely to persist. What is the important factor distinguishing them?
What is the most effective way to keep a very large continent habitable, without chopping it up into a lot of ordinary continents?