a) On average, there is one virus particle for every bacterial cell on earth
b) The human body plays host to ten bacterial cells for each one of its own
c) Microbial cells have been in existence for at least 3.5 billion years
d) Metazoans originated at least 750 million years ago, but may be much older
e) There are 10 million microbes on earth for each star in the universe
