1.b.3 – What have been the next forms of life?

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December 14, 2009 — Riccardo Sabellotti - Giacinto Sabellotti

What have been the next forms of life?

The study of genetics leads us to think that all forms living today are descendants from a single common ancestor; all cells of all known organisms base in fact their operation on the same type of molecule, the DNA, which incorporates the same encrypted language: the genetic code.
This ancient ancestor, presumed similar to the existing bacteria, subject to different environmental conditions, adapted itself under the circumstances and gave rise to new species; these species have also done the same, producing always evolving chains ready for new branches.
One of the first activities of bacteria was the fermentation, which is the decomposition of sugars to create the necessary energy to all cellular processes; such process allowed the bacteria to live thanks to chemicals existing in the land and water. Some of these bacteria developed a capacity of the greatest importance: to absorb nitrogen from air and transform it into various organic compounds. Nitrogen is a component of protein present in every cell and even today all living organisms, to survive, depend on the bacteria that fix nitrogen.
The bacteria also developed photosynthesis, a process that became the source of primary energy for life, although very different from that practiced by the current plants. All these survival strategies allowed the bacteria not only to live and evolve, but also to begin to alter the environment, maintaining, through their adjustment processes, the conditions for the development of life.
A new type of bacteria at some point developed a new process of photosynthesis capable of extracting hydrogen from water, releasing oxygen in the air. But this oxygen became at some point too much; oxygen pollution produced, approximately two billion years ago, an unprecedented disaster and the whole bacterial organization had to reorganize in order to survive.
The crisis of oxygen started an evolutionary process that brought to the appearance of cyanobacterial, who used their oxygen, the harmful substance, through aerobics respiration, based on the consumption of that element. Life was forever changed and so the environment in which evolving; the amount of free oxygen in the atmosphere stabilized to 21 per cent and it is to be noted that if this value would go below 15 percent, nothing would burn and bodies, unable to breathe, would die; above 25 percent instead everything would burn, combustion would be spontaneous and the flames would swallow the Earth. From millions of years the community of bacteria and their descendants maintain oxygen in the quantity ideal for the life of plants and animals.
It should be noted that not always living beings can adapt to various situations that arise; in that case their chain stops, which means that not only there will not have new species, but also the old one can disappear, that is to extinct.
The enormous variety of life forms has made it impossible that all the species would extinct for inability to adapt; among many species there are always many who manage to survive and to further differentiate. This is demonstrated by the fact that bacteria not only still exist in large numbers and in every part of the planet, but they also produced new forms of life, so complex and so different from them, to be classified as separate groups; among these, there are the protistis, beings formed by a single cell like bacteria, but with a nucleus containing the DNA and other internal structures managing the activities of the cell; this structure is also that of cells that make up our body and the body of every animal or plant.
Encouraged by genetic studies, it is considered therefore that all living beings formed by many cells, called multicellular, derived from these beings, and every form of life visible to the naked eye can therefore be seen as a huge and complicated colony of protists.