The Tree of Life is first mentioned at Genesis 2:9 in the middle of the Garden of Eden. Many ancient cultures mention a tree of life.  Evolutionists have long used a tree of life to describe the origin of life on planet earth, including Charles Darwin, who had only one illustration in his book, On the Origin of Species (1859) designated the 'tree diagram.' "The expression tree of life was used as a metaphor for the phylogenetic tree of common descent in the evolutionary sense in a famous passage by Charles Darwin (1872)." 
Evolutionists have drawn many ‘tree of life’ diagrams (Wikipedia reports nearly 500 published trees) and one such diagram below shows a ‘last universal common ancestor’ (LUCA) as the trunk and the three domains (bacteria, archaea and eurokoyte) as branches of that trunk.
All organisms are divided into two main divisions, prokaryote and eukaryote. The prokaryotes are further divided into bacteria and archaea. These are referred to as the three domains; bacteria, archaea (organisms without a nucleus) and eukaryote (organisms with a nucleus). The relationship between the three domains is of central importance for understanding the origin of life according to evolutionists. What is interesting about this is that the above tree diagram, as well as many others used by evolutionists, omit viruses and bacteriophages.
Viruses are by far the most abundant biological entities on Earth and they outnumber all the others put together. "The origins of viruses in the evolutionary history of life are unclear: some may have evolved from plasmids—pieces of DNA that can move between cells—while others may have evolved from bacteria."  "However, plasmids, like viruses, are not generally classified as life."  "A virus is a small infectious agent that replicates only inside the living cells of other organisms. Viruses can infect all types of life forms, from animals and plants to microorganisms, including bacteria and archaea."  Scientists debate whether viruses are "organisms at the edge of life” even though they replicate and contain DNA/RNA. So in the above tree diagram, viruses are included by inference because they exist in all living cells of the two main divisions of life but are not mentioned even though viruses outnumber both prokaryote and eukaryote.
Bacteriophages are ubiquitous viruses, found wherever bacteria exist. It is estimated there are more bacteriophages on the planet than every other organism on Earth, including bacteria, combined and have been around for 3 billion years. 
“The transition from non-living to living entities was not a single event, but a gradual process of increasing complexity that involved molecular self-replication, self-assembly, autocatalysis and cell membranes.” 
According to evolutionists, bacteria were among the first life forms to appear on Earth, and are present in most of its habitats, forming a biomass which exceeds that of all plants and animals. Archaea are particularly numerous in the oceans, and the archaea in plankton may be one of the most abundant groups of organisms on the planet. Archaea are a major part of Earth's life and may play roles in both the carbon cycle and the nitrogen cycle and are also part of the human microbiota, found in the colon, mouth, and skin. "Although probable prokaryotic cell fossils date to almost 3.5 billion years ago, most prokaryotes do not have distinctive morphologies and fossil shapes cannot be used to identify them as archaea....Since the Archaea and Bacteria are no more related to each other than they are to eukaryotes, the term prokaryote's only surviving meaning is 'not a eukaryote', limiting its value." 
Eukaryotes represent a tiny minority of all living things. However, due to their generally much larger size, their collective worldwide biomass is estimated to be about equal to that of prokaryotes. Eukaryotes evolved approximately 1.6–2.1 billion years ago, during the Proterozoic eon. ]7]
The age of the universe is generally accepted at 13.8 billion years, while the age of the earth is generally accepted to be 4.5 billion years. 
The last universal common ancestor (LUCA) "is estimated to have lived some 3.5 to 3.8 billion years ago in the Paleoarchean era, a few hundred million years after the earliest evidence of life on Earth,"
To simplify this timeline the following football field of 100 yards represents the age of the earth with the red H representing the birth of the planet, and the yellow V as the present day, with the timeline of 4.5 billion years. Each yard on this field equals 45,000,000 years (five years equals 225 million years, ten yards equals 450 million years).
The LUCA (blue L) would be placed on this timeline around the ten yard line near the red H with the prokaryotes showing up immediately following. The eukaryotes show up in the timeline around the 45 yard line on the yellow V side of the field.
The vertebrates show up during the timeline in the Cambrian period which is just shy of the ten yard line which is known as the 'Cambrian Explosion' that "produced the first representatives of all modern animal phyla." 
Figure 3: Football field timeline for the age of the earth and the two main divisions of life, prokaryote and urkaryote.
All three divisions still have life forms living today that are represented in the fossil record which is a timeline written in stone, a more reliable time line than any other. Some of the life forms found in this fossil record show extinct life forms, but many ancient life forms of plants and animals are extant and look exactly like those shown in the fossil record and are said to be billions of years old because the bacteria found in the fossil record are still extant today. The tree diagram on this page at Wikipedia depicts how archea and eukarya are more closely related to each other than to bacteria. Of course, there is no fossil record of the LUCA ever found, so it is presumed to have existed. Microbial mat fossils have been found in 3.48 billion-year-old sandstone from Western Australia, while biogenic graphite has been found in 3.7 billion-year-old metamorphized sedimentary rocks from Western Greenland. Recent studies have tentatively proposed evidence of life as early as 4.28 billion years ago. 
Why No Transitional Fossils?
A fundamental central thesis of evolution is the assumption of the descent of all living species from a common ancestor depicted in many of the published evolution tree of life diagrams. Usually the reason proposed by evolutionists why there are no fossil records of the transitions from the LUCA to the three major domains, not to mention the major transitions from fish to amphibian to reptile to birds and mammals, are simply excuses, since evolutionists point out they have evidence of bacteria fossils that are nearly 4 billion years old. Why are there no transitional fossils during this 4 billion year record? There are fossils in the Cambrian period of soft bodies like jellyfish, coprolites, earthworms, flatworms, priapulids, flowers, plants, and the list goes on. Why are there not any fossils before or during the Cambrian period indicating transitions? Why the Cambrian Explosion?
Tree of Life
The tree of life diagrams that evolutionists use illustrate 'a ladder-like progression from lower into higher forms of life.' i.e., LUCA > Prokarya and Eukarya [see Figure 2] and a typical tree diagram shown below in a biology textbook shows this lower to higher forms of life:
The diagram above shows a timeline starting at 550 mya to the fossils of mammals and birds, 400 million years, which is shown on the Figure 3 diagram in the yellow line from the eleven yard line to the three yard line. During these 400 million years there are no transitional fossils between these major life forms. Why are these transitional fossils missing? When a timeline is written in stone, the record stands out and speaks for itself. Another tree diagram example is below:
Firgure 5: Phylogenetic tree of all vertebrate animals
Image by David Lin, adapted from image by Petter Bøckman, Wikimedia Commons
When you look at the above tree it is assumed that the branches and leaves connected to the trunk extends its roots to the eukarote which shows up in the fossil record in Figure 3 near the 45 yard line (yellow side) without any fossil transitions connecting to the LUCA. Some transitional fossils may be proposed but they are debated by scientists whether they are the transitions hoped for. There is no consensus among evolutionists on how the fossil record supports the central fundamental assumption of the descent of all living species from a common ancestor. In fact, the fossil record supports the conclusion that life forms emerge from non living matter independently and completely separate from previous life forms. If evolutionists accept the concept of abiogenesis  with the LUCA, why couldn't this happen with other major life forms?
Indeed, a New York Times Magazine article, states, "The tree of life is not a tree." This article is about Carl Woese who is famous for defining the archaea and pioneered the work of molecular phylogenetics which Woese described in 1969 as an 'internal fossil record' and together with Charles E. Fox redrew the taxonomic tree into the three-domain system, based on phylogenetic relationships rather than obvious morphological similarities. The result of all this after many years of studying horizontal gene transfer is an unusual tree shown below:
Figure 6: Ford Doolittle’s reticulated tree. Image Courtesy of Ford Doolittle and the A.A.A.S.
Since the fossil record hasn't explained satisfactorily the central thesis of evolution that assumes the descent of all living species from a common ancestor, the evolutionists have turned to the study of phylogenetics to validate the theory. As David Quammen wrote in his book, The Tangled Tree: A Radical New History of Life, the evolution's tree of life is indeed tangled, difficult to explain at best, and looks in the above illustration more like a banyan tree.
Just because all life forms have some gene sequences in common does not necessarily mean that present day life forms all came from a common ancestor. The 'banyan' tree of life diagram as shown above, Doolittle's reticulated treee, simply shows that all life forms originated on earth and have elements in common, .i.e., nutrients, oxygen, etc. Bacteria, archaea and eukarya simply emerged independently and share common RNA/DNA traits. The tree of life comes out of earth's dust.
The deeper issue to the fundamental central thesis of evolution and the assumption of the descent of all living species from a common ancestor is whether the LUCA originates from abiogenesis and what causes abiogensis? If evolutionists believe that the LUCA orginated not on earth but somewhere in outer space, then you push this deeper issue so farther out that is beyond the reach of any scientific method to analyze. One article on this subject states, "some scientists contend that abiogenesis was unnecessary, suggesting instead that life was introduced on Earth via collision with an extraterrestrial object harbouring living organisms, such as a meteorite carrying single-celled organisms; the hypothetical migration of life to Earth is known as panspermia." . It is of interest to note, that while three nucleobases (adenine, guanine and uracil) have been discovered on meteorites, cytosine and thymine have not. Does it really make any sense to speculate that the five known nucleobases must have originated from outer space when all five exist on planet earth without any doubt? What caused the abiogenesis to occur way out in outer space?
If the abiogensis of the LUCA originated here on planet earth what caused this to occur? And what evidence is there that this cannot happen again and again with different life forms? In one article on abiogenesis it states, "Some scientists have proposed that abiogenesis occurred more than once."  Why does the evolutionist phylogenetic tree of life always assume a common ancestor? Why couldn't there be multiple trees of life? Is it because the evolutionists can't see the forest for the trees?
A Forest of Trees of Life
There are many biologists and scientists who have a forest of trees showing where life originated, i.e., example below:
Figure 7: Trees of Life
 Tree of Life, Wikipedia
Darwin and the Tree of Life: the roots of the evolutionary tree, Nils Petter Hellstrom, Archives of natural history 39.2 (2012): 234–252 Edinburgh University Press
 Virus, Wikipedia
 Plasmid, Wikipedia
 Bacteriophage Evolution and the Role of Phages in Host Evolution, Robert W. Hendrix, ASM Science
 Abiogenesis, Wikipedia
 Archea, Wikipedia
 Eukaryote, Wikipedia
 WYHAT (see end notes 3 and 4)
 Cambrian, Wikipedia
 LUCA, Wikipedia
 Abiogenesis, Encyclopedia Britannica