There is no easy way to describe what the first organism might be, because living things slowly evolved from the molecules without passing clear limits separating life from life. “There was no living thing yesterday, but it exists today.” There was no definite point in time when you could.
Here are some of the oldest fossils found so far:
They are thought to be at least 3.5 billion years old, perhaps even older. Microbiologists think that they look like modern bacterials, but to me, they seem to be blurred. In the next picture, the black-and-white diagram shows how microbiologists interpret these blobs.
It’s hard to be sure that they are real or not, with something fuzzy and obscure. In this case, researchers looked at the ratios of the different carbon isotopes and discovered that the fossils have the expected lighter carbon (C12) version. Living creatures prefer to use Carbon 12 on other forms; I can explain this more.
Indirect studies provide some information about what a scientist called LUCA, the last universal common ancestor. There are three areas of life, bacteria, archaea and eukaryotes. The first two are a group of complicated organisms arising from the combination of bacteria, eukaryotes, an archaeal and bacteria, which ordinary people call microbes.
On this basis, LUCA:
- You did not have a cell membrane, or at least there are organisms like this.
- Instead of DNA, RNA was used as genetic material.
- The DNA did not multiply, but it probably had some DNA.
- ATP is used for energy as modern organisms do.
- Produced proteins that use modern genetic code from RNA, possibly using transcription RNA as modern organisms do.
- Hydrogen combined with CO2 to produce both energy and organic chemicals. This diagram shows some of the biochemical pathways that LUCA may have.