A new international study, published in *Science*, produces the first global maps estimating where arbuscular mycorrhizal fungi occur and how much fungal biomass their underground networks contain. The research focuses on arbuscular mycorrhizal fungi, which form extensive hyphal networks in soils and support plant growth by exchanging nutrients and water with most land plants. Across the planet, the study estimates that these fungi are widespread and reach extremely large total spatial scales, helping plants obtain resources while also drawing carbon into soils. This soil carbon storage is linked to climate regulation. The *Science* report also describes the networks as ancient, noting they have been forming for hundreds of millions of years. By combining large-scale estimation with newly compiled mapping approaches, the work aims to quantify the true extent of these subterranean systems rather than relying only on localized observations. Together, the reported results characterize the global distribution and estimated mass of these fungal networks and their ecological role in sustaining vegetation and influencing Earth’s carbon cycle.