Archaea are a group of single-celled microorganisms that are distinct from bacteria and eukaryotes. They are known for their ability to thrive in extreme environments, such as hot springs, salt lakes, and deep-sea vents. Archaea have unique biochemical properties, including distinct cell membranes and metabolic pathways. These organisms play essential roles in various ecosystems, particularly in nutrient cycling and energy production. Some archaea are involved in processes like methanogenesis, which produces methane, a potent greenhouse gas. Their study helps scientists understand the diversity of life on Earth and the potential for life in extreme conditions elsewhere in the universe.