Question: Where did unicellular microorganisms evolve from?
About the article "Bacteria", section "Origin and early evolution".

Candidate passages:
Bacteria and Protists form two separate animal kingdoms, but both are fairly similar when compared.
Bacteria are prokaryotic microorganisms, while protists are a group of eukaryotic organisms.
Because both are microorganisms, both fall under the study of microbiology and special techniques are required for archaeologists to even see them.
Archaeologists, in order to find these microorganisms in a site, have to first take samples from the site and bring them in for lab analysis.
Once in the lab, they can use equipment such as optical microscopes, in order to actually see evidence of micro organic remains.
Archaeologists that look at these microorganisms do not actually find the living bacteria or protist, but instead find indentations left behind in material from where they had did.
Depending on where the indentations were in the strata, archaeologists can determine the age of the microorganisms. 
This section contains a list of publications on microbiology.
Microbiology is the study of "microorganisms", which are defined as any microscopic organism that comprises either a single cell (unicellular), cell clusters or no cell at all (acellular). 
Microbiology (from Greek , "mīkros", "small"; , "bios", "life"; and , "-logia") is the study of microscopic organisms, either unicellular (single cell), multicellular (cell colony), or acellular (lacking cells).
Microbiology encompasses numerous sub-disciplines including virology, mycology, parasitology, and bacteriology.
Eukaryotic microorganisms possess membrane-bound cell organelles and include fungi and protists, whereas prokaryotic organisms—which all are microorganisms—are conventionally classified as lacking membrane-bound organelles and include eubacteria and archaebacteria.
Microbiologists traditionally relied on culture, staining, and microscopy.
However, less than 1% of the microorganisms present in common environments can be cultured in isolation using current means.
Microbiologists often rely on extraction or detection of nucleic acid, either DNA or RNA sequences.
Viruses have been variably classified as organisms, as they have been considered either as very simple microorganisms or very complex molecules.
Prions, never considered microorganisms, have been investigated by virologists, however, as the clinical effects traced to them were originally presumed due to chronic viral infections, and virologists took search—discovering "infectious proteins".
As an application of microbiology, medical microbiology is often introduced with medical principles of immunology as "microbiology and immunology".
Otherwise, microbiology, virology, and immunology as basic sciences have greatly exceeded the medical variants, applied sciences. 
Historical classifications.
The first division of the protists from other organisms came in the 1830s, when the German biologist Georg August Goldfuss introduced the word "protozoa" to refer to organisms such as ciliates and corals.
This group was expanded in 1845 to include all unicellular animals, such as foraminifera and amoebae.
The formal taxonomic category "Protoctista" was first proposed in the early 1860s by John Hogg, who argued that the protists should include what he saw as primitive unicellular forms of both plants and animals.
He defined the Protoctista as a "fourth kingdom of nature", in addition to the then-traditional kingdoms of plants, animals and minerals.
The kingdom of minerals was later removed from taxonomy by Ernst Haeckel, leaving plants, animals, and the protists as a “kingdom of primitive forms”.
In 1938, Herbert Copeland resurrected Hogg's label, arguing that Haeckel's term "protista" included anucleated microbes such as bacteria, which the term "Protoctista" (literally meaning "first established beings") did not.
In contrast, Copeland's term included nucleated eukaryotes such as diatoms, green algae and fungi.
This classification was the basis for Whittaker's later definition of Fungi, Animalia, Plantae and Protista as the four kingdoms of life.
The kingdom Protista was later modified to separate prokaryotes into the separate kingdom of Monera, leaving the protists as a group of eukaryotic microorganisms.
These five kingdoms remained the accepted classification until the development of molecular phylogenetics in the late 20th century, when it became apparent that neither protists nor monera were single groups of related organisms (they were not monophyletic groups).
Some protists, sometimes called ambiregnal protists, have been considered to be both protozoa and algae, and names for these have been published under either or both of the "ICN" and the "ICZN". 
A unicellular organism, also known as a single-celled organism, is an organism that consists of only one cell, unlike a multicellular organism that consists of multiple cells.
Historically the simple single celled organisms have sometimes been referred to as monads.
The main groups of unicellular organisms are bacteria, archaea, protozoa, unicellular algae and unicellular fungi.
Unicellular organisms fall into two general categories: prokaryotic organisms and eukaryotic organisms.
Unicellular organisms are believed to be the oldest form of life, possibly existing 3.8 billion years ago.
Prokaryotes, most Protista, and some fungi, are unicellular.
Although some of these organisms live in colonies, they are still unicellular.
These organisms live together, and each cell in the colony is the same.
However, each individual cell must carry out all life processes to survive.
In contrast, even the simplest multicellular organisms have cells that depend on each other to survive.
Some organisms are partially uni- and multicellular, like "Dictyostelium discoideum".
The other can be unicellular and multinucleate, like Myxogastria and "Plasmodium".‘"Candidatus" Magnetoglobus multicellularis’, related to Deltaproteobacteria, is a multicellular prokaryote.
It is neither unicellular, nor a colony.
Most unicellular organisms are of microscopic size and are thus classified as microorganisms.
However, some unicellular protists and bacteria are macroscopic and visible to the naked eye.
Examples include: Xenophyophores, protozoans of the phylum Foraminifera, are the largest examples known, with "Syringammina fragilissima" achieving a diameter of up to  "Nummulite", foraminiferans "Valonia ventricosa", an alga of the class Chlorophyceae, can reach a diameter of  "Acetabularia", algae "Caulerpa", algae "Gromia sphaerica", amoeba "Thiomargarita namibiensis" is the largest bacterium, reaching a diameter of up to 0.75 mm "Epulopiscium fishelsoni", a bacterium