Humans have made 30 trillion tons of junk throughout modern existence. All that junk has a geological term: the technosphere, which is broken down into urban, rural, subterranean, marine, and aerial areas, Seeker reports. The goal was to quantify the scale and diversity of it all, as published in a paper in The Anthropocene Review this week. The research took a lot of estimation and some hypothetical paleontology. The aerial technosphere alone, for example, holds almost one trillion tons of carbon dioxide created by human activity. But they broke it down much further than that. They called each object, like a cellphone, technofossils. Consider the cellphone: 6.8 billion phones have been made, but even those could be divided into subcategories or technospecies, like iPhone or Samsung. (And then there are makes and models, too.) By that example and others like it, they estimate categorizing everything would require billions of classifications. The researchers admit this is a broad stroke figure, but it’s, quite literally, a massive undertaking. They even suspect it is “bigger than the number of living species on Earth,” which is kind of a haunting thought to sit with.