Bacteria

Bacteria simply dominate the Earth. Scientists often refer to the Age of the Dinosaurs or the Age of Mammals or discuss the immense diversity and abundance of insects. But, bacteria are the oldest, most diverse, most abundant organisms on Earth. They always have been and, most likely, always will be.

Bacteria are able to live in a wide variety of environments. They have been found in the intestines of vertebrates, around volcanic vents at the bottom of the ocean, and in swamps where there is no oxygen. Though some bacteria are rather fragile and will be killed by soap and water, there are some species that are resistant to extreme temperatures, most antibiotics, and perhaps even the vacuum of space.

Of course, the bacteria of most interest to humans are the species that cause diseases. Most bacteria are quite harmless to humans, but a few cause diseases such as leprosy, cholera, and bubonic plague. Though viruses such as HIV, Hanta, and Ebola receive more media attention and research money, the bacteria that cause diseases have been around for a much longer time and have killed far more people.