Novel ecosystems are human-built, modified, or engineered niches of the Anthropocene. They exist in places that have been altered in structure and function by human agency. Novel ecosystems are part of the human environment and niche (including urban, suburban, and rural), they lack natural analogs, and they have extended an influence that has converted more than three-quarters of wild Earth [citation needed]. These anthropogenic biomes include technoecosystems that are fuelled by powerful energy sources (fossil and nuclear) including ecosystems populated with technodiversity, such as roads and unique combinations of soils called technosols. Vegetation associations on old buildings or along field boundary stone walls in old agricultural landscapes are examples of sites where research into novel ecosystem ecology is developing.