 Microorganism, a micro-organism, or microbe, is a microscopic organism, which may exist in its single-celled form or in the colony of cells. The possible existence of unseen microbial life was suspected from ancient times, such as in Jain scriptures from 6th century BC India and the 1st century BC Bukan agriculture by Marcus Tarenti Eusebaryl. Microbiology, the scientific study of microorganisms, began with their observation under the microscope in the 1670s by Anton Yevann Levenhoek. In the 1850s, Louis Hastor found that microorganisms caused food spoilage, debunking the theory of spontaneous generation. In the 1880s Robert Koch discovered that microorganisms caused the diseases tuberculosis, cholera and anthrax. Microorganisms include all unicellular organisms and so are extremely diverse. Of the three domains of life identified by Carl Woes, all of the archaea and bacteria are microorganisms. These were previously grouped together in the two-domain system as prokaryotes, the other being deukaryotes. The third domain eukaryote includes all multicellular organisms and many unicellular progests and protozones. Some progests are related to animals and some to green plants. Many of the multicellular organisms are microscopic, namely microanimals. Some fungi and some algae, but these are not discussed here. They live in almost every habitat from the poles to the equator, deserts, geysers, rocks and the deep sea. Some are adapted to extremes such as very hot or very cold conditions, others too high pressure and a few such as Dano-Kakus-Radilaturans too high radiation environments. Microorganisms also make up the micro-BOTA found in and on all multicellular organisms. The December 2017 report stated that 3.4 billion-year-old Australian rocks once contained microorganisms, the earliest direct evidence of life on Earth. Microbes are important in human culture and health in many ways, serving to ferment foods, treat sewage, produce fuel, enzymes and other bioactive compounds. They are essential tools in biology as model organisms and have been put to use in biological warfare and bioterrorism. They are a vital component of fertile soils. In the human body micro-organisms make up the human micro-BOTA including the essential gut flora. They are the pathogens responsible for many infectious diseases and as such are the target of hygiene measures.