Most life on Earth is microbes. we've only just scratched the surface of the microbial realm. Probably less than .1% of microbes have been classified let alone cultured or had their genes sequenced, so really that microbial realm is a mystery. — Paul Davies Copy Share Image
The vast majority of terrestrial species are in fact microbes, and scientists have only begun scratching the surface of the microbial realm. It is entirely possible that examples of life as we don't know it have so far been overlooked. — Paul Davies Copy Share Image