A curious reader asked us what was the first species of living being to appear on Earth. Thank you for this fascinating question.
By responding, we will travel back in time to the infinity of the past! The first living beings appeared more than 3.8 billion years ago.
It is such a distant past. We (the human species) have existed for about 3 million years, so it is difficult for us to know exactly what the first species was like.
Still, we have a little idea:
The first living beings appeared very surely at the bottom of the oceans.
Life and its primordial components appeared near hydrothermal vents: chimneys through which gases escape from the bottom of the oceans and meet salt water.
This encounter allows quick and easy chemical reactions, some of which are still part of our metabolism (reactions that are found in our cells).
This primitive life could not move away from the hydrothermal sources because they are an inexhaustible source of energy (primitive food).
To make it go away, he had to create, among other things, a membrane that is like a suitcase to fit inside and store energy.
The details of this release are still little known to researchers. To know more, they are trying to recreate life, but they are also looking for clues, on Earth and in the oceans.
The most ancient fossils
It has been established that the oldest fossils come from bacteria that lived more than 3.4 billion years ago.
In fact, these fossils, the stromatolites, are mineral structures of limestone that were formed by colonies of bacteria.
Bacteria are very simple, a single cell where everything is mixed up inside. On the contrary, in the cells of our body, there are many arrangements to separate the activities of information storage, protein manufacture or “digestion”.
Bacteria dominated life on Earth for 1.5 billion years before more complex organisms appeared. It is not known if these bacteria were the first, the only ones, or how they lived.
The most recent ancestor of all known living beings
Fortunately, thanks to Darwin, who discovered that all living things are related, and thanks to Rosalind Franklin, Watson and Crick who photographed DNA, we can read the genes of all living things that now exist on Earth.
Thus we can compare the genes between species and play the game of differences, but also the game of comparisons.
This allows us to better understand who was the most recent ancestor of all known species.
In English, this common ancestor is called “LUCA”, after Last Universal Common Ancestor.
What is found identically in all living species?
We have learned that living beings are grouped into three main groups: bacteria, archaea and eukaryotes.
Archaea are similar to bacteria, they have been confused with bacteria for a long time, however their way of functioning is very different, we will talk about this a little later.
As for eukaryotes, they are all living beings whose cells have nuclei. We know that the first groups to appear are bacteria and archaea.
Eukaryotes appeared later, one or two billion years ago, and also have an eventful history.
But let’s go back to our first beings: bacteria and archaea!
Taking the game of comparisons one step further, we can describe everyone’s common ancestor.
Therefore the ancestor of bacteria and archaea, as a single cell already capable of reproduction, feeding like plants (of chemical compounds), loving hot water without oxygen, and with a membrane (remember, the membrane is like a suitcase to be transported).
This cell is capable of using the same energy as our cells and also contains genes.
It is good that at that time the Earth is dominated by the sea, dotted with a few volcanic islands.
Volcanic activity, very important, makes life in the water hell. The air is dense, cloudy and without oxygen.
One or more ancestors?
Except that bacteria and archaea do not have the same membranes! So, perhaps, LUCA had a simple membrane that was later modified.
But how can you be sure? How can you not consider several common ancestors, a “population” of cells with many different membranes (or bags), most of which would have died out to leave room only for bacteria and archaea.
The mystery surrounding the membranes is not the only one. Other characteristics are profoundly different between archaea and bacteria.
However, they share essential elements that suggest that their ancestors lived close to each other at one time or another.
In general, it is difficult to reconstruct the stages between the appearance of life and the appearance of cells, bacteria and archaea.
What was the diversity of these first living beings? How did they leave the hydrothermal vents?
I read in an article that at this stage of life, the dependencies and interactions between living beings were very important in number and intimacy. They could easily copy parts of their neighbors’ genetic information and create chimeras or hybrids (a mixture of two beings).
So, if you want to follow in the footsteps of the first living beings, you must know that you have to know not only about biology, but especially about chemistry.
To go further:
Among the first components of living beings, shared by almost all organisms, are found
- Energy in the form of ATP
- The Krebs cycle, which produces energy, ATP, from organic molecules (it is a sequence of chemical reactions), can also be reversed to produce organic molecules of ATP, RNA and DNA
The differences can be found, among others, in :
- Membranes capable of chemosis to store energy (like a hydraulic dam, but here we do not store water on one side but water with different electrical charges).
- The way to copy the DNA.
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