in reply to Future historians will find that the material characteristic of the current era is...
I suppose it depends on what materials that we commonly use become less common in the future. Plastic seems obvious at first, but on further consideration I suspect that we've really only just *begun* to use plastic, and it will probably be rather a long time before plastics reach their peak. If so, the current era may end up with some other characterization.
Perhaps the more interesting question: which information formats will future historians associate with our era?