Microbes Quiz Bacteria, fungi and viruses are all considered microbes. (True or False) The human body has about 10 trillion cells but is "home" to about 100 trillion microbes. (True or False) Your intestines contain several pounds of bacteria. (True or False) Microbes make up 60% of Earth's biomass. (True or False) Microbes are the oldest creatures; first appearing on Earth about 3.8 billion years ago. (True or False) Microbes generate at least 50% of the oxygen in the atmosphere. (True or False) Less than 1% of the millions of microbial species have been identified. (True or False) Microbes outnumber all other creatures and make up most living matter. (True or False) Microbes thrive in extreme environments like hot springs, where few other life forms can exist. (True or False) Most microbes (95%) do not cause disease. (True or False) Microbes are studied as a source of new genes and organisms for bioremediation (healing environmental damage), biotechnology and energy production. (True or False) Microbial diversity can be used to study and predict environmental changes. (True or False)