This project will study the chemistry of archeological waste in ancient archaeological deposits for clues on the development of animal domestication and associated growth in early human populations. From a geochemical perspective, archaeological sites are highly dynamical features, a complex and overlapping mixture of human and natural sediments and dissolved constituents. Tens of studies over the past two decades have explored these rich geochemical records, providing a new perspective on many aspects of human behavior and human surroundings, their use of space, and plant and animal management. However, such studies have generally overlooked the salt chemistry of ancient archeological sites, and its implications. This is a missed opportunity, especially in some arid land sites where post-occupation modification can be minimal and closed-system retention of some elements is likely. This project proposes to further develop a new way of looking at the geochemistry of arid land archeological sites as a whole, using mass balance modeling. This approach quantifies soluble salt additions and losses to a system to understand the onset and evolution of animal domestication. Results so far demonstrate the power of this model approach for understanding changes in site-use intensity and livestock management over an approximately thousand-year time span.The salt chemistry of the refuse is dominated by animal and human urine salts, which increased steadily over the long term occupation, a reflection of expanding human and domesticated animal populations. The project will also analyze dung biomarkers, ancient gut microbiomes, and pathogens (e.g. Salmonella) that are associated with human and animal waste at the site. This should lead to a better understanding the relationship between animal waste products and ancient pathogens and provide information about disease source and spread. This project will support training of three early career scientists in a variety of geochemical and field monitoring techniques. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.