Researchers collect samples at deep wells, such as this oil well in Utah, to improve our understanding of geochemical cycles and microbial life beneath Earth’s surface. Credit: Jennifer McIntosh Much of Earth's water is hidden hundreds of meters beneath our feet, among soil particles and deep within rock pores and fractures. Mining, oil and gas production, water wells , and other human activities involve extracting various fluids from or injecting them into the ground. Much attention has been pa...