This is sometimes known as the Argument From Complexity, or the Argument From Ignorance, or the Argument From Incredulity.
It has the form:
This a very weak form of argument, regardless of context. Basically, it says that if I don't know something, then no one else knows, and no one ever will.
In short, it is not actually a logical argument. It is simply an affirmation of bafflement or wonder. Suppose I leave a saucer of milk outside overnight. In the morning, the milk is gone. I can't think of anything but fairies that might have visited my yard. So, the missing milk is proof of fairies. Right?
It is also an affirmation of pessimism. Scientific breakthroughs occur regularly, but the arguer is confident that there will never ever be one about this subject.
Here's an example from The Blind Watchmaker: