Tree of life
In order to organise all of the forms of life on earth, scientists created the tree of life. All of the different types of organisms that now live on earth, or that we know once lived on earth, are included in the tree. Every group has its own branch: from mammals (including people) to birds and reptiles And the thick branches fan out into thinner branches for different species.
Enormous diversity
It’s a little different with microorganisms. For convenience, they’re all called ‘microorganism’, since they’re invisible to the naked eye. But that name doesn’t do justice to the enormous diversity within the group. Microbes make up a huge part of this tree of life. Life on earth once began with microorganisms, and they still make up more than two-thirds of the branches on the tree. Compared to these branches, the branches of visible life are small and thin.
Living or not?
As opposed to all other sorts of microbes on earth, viruses are not represented in the tree of life. Viruses don’t swim, don’t eat, don’t grow, and cannot reproduce independently. Viruses rely on a living host to do that. Because they lack all of these characteristics, many scientists do not recognise viruses as living organisms.