One secrecy of Life.
On one of those reflective days in 2015, it came to my mind that – maybe – during this year a baby would be born that, once as an adult, would become the first human to put his/her footprint on our neighbouring planet Mars, searching for clear evidence of life – past or present.
And then I started wondering about how life on Earth might have come about...
Definition of Life.
To find a proper definition of life is tougher than I first thought. Consulting scientific sources gave me a vast amount of definitions, but all of them were challenged by peers. So, for the objective of this small article, let's not waste too much time on this and let us accept the following simple description of life:
"Life is a dynamic process, concealed in a closed unit (cell) that transforms energy and matter via self-sustaining chemical and physical activity in order to be able to increase in biomass, to constantly interact with its environment and to reproduce itself in an autonomous way – all this together, called metabolism".
Speculation about the start and first forms of Terrestrial Life.
All forms of life on Earth – past and present – as we know them today, have the same fundamental biochemical mechanisms. All of them use the nucleic acid transcription concept to proliferate and only the family of viruses does need a host for it.
It is widely accepted in the scientific community that this similarity of concept reflects a common descent, and recent consensus tends to accept the model of simultaneous synthesis of both vital components for life some 3,7 – 4,4 billion years ago: chains of molecules to create DNA/RNA for genetic coding and other chains of molecules to create a cell membrane.
It has been hypothesised that the geological conditions on Earth at that time, combined with organic molecules recently found in sediments, and reactive components supplied by meteorites during the Late Heavy Bombardment could have resulted in bio-molecules, like RNA, basis for the genetic code.
Fact is that microbial fossils from 3,48 billion years ago have been found in Australia and other clear indications for life – from 3,7 billion years ago in Western Greenland.
A hypothesis about the first forms of life is that it all started through a primitive blueprint for viruses, as we know them today. Viruses are sometimes called to be "at the edge of life" because they possess genes, evolve by natural selection and replicate, but they do need a host to replicate. Viruses seem to be a very old remnant of the first attempts of life to start up. Parallel to that, there must have been the concept of metabolism.
Random synthesis of complex organic molecules.
For those readers to which the hypothesis of randomly created complex organic molecules on Earth seems to be "an easy way out to explain a complicated matter", recent investigations resulted in a multitude of proven existence of complicated molecules on cosmic dust, comets, in stellar systems and in the atmosphere of some planets.
As it looks today, life might not be so "exclusive" to our Earth, but merely an "inevitable consequence of physics and chemistry" – even in space. For that reason, NASA's Curiosity and Opportunity rovers will now be searching for evidence of ancient life and organic carbon on the planet Mars and will start a searching program on complex organic matter in the universe.
Evolution and game-changing conditions.
Once the concept of genetic material, concealed in a closed unit – a proto cell – and metabolism, was generated, evolution could start. For millions of years, anaerobic cell population was the dominating species. Until...
Cyanobacteria started to proliferate about 3,5 billion years ago. They use photosynthesis to generate their food. A consequence of this metabolism is that oxygen is formed. At that time oxygen was a highly poisonous gas. The oxygen atmosphere that we depend on today was generated by numerous cyanobacteria, some 3 to 2,5 billion years ago. Before that time, the atmosphere had a very different chemistry, unsuitable for life as we know it today. Cyanobacteria live in the water, are quite small and they often grow in colonies large enough to be seen by the naked eye. One ancient witness of those colonies are the fossil stromatolites, a structure of calcium carbonate and cyanobacteria. Even today we can find those structures along shores with highly-saline water.
Cyanobacteria are also the cause for the huge iron ore mines we have today. As they generated oxygen as a by-product of photosynthesis, the iron dissolved in the oceans started to oxidise, resulting in iron-oxide (rust) that precipitated. Oceans at that time were brown and muddy. (One hypothesis about the red colour of the planet Mars is that it might be generated by iron-oxide, also formed by ancient oxygen-generating life forms, like on Earth).
Cyanobacteria are arguably the most successful group of microorganisms on earth. They even can incorporate themselves in other living organisms; in fact the chloroplast – the organelle that conducts the photosynthesis – in plants is a cyanobacterium, taken up by a green algal ancestor of the plants some 4-1 billion years ago. In this way, cyanobacteria were making food for the host in return for a home and doing so, they contributed to the origin of plants.
Mitochondria – the energy-producing components in a nucleus-containing cell – are the result of the engulfment of a complete bacterium.
Another important example of "captive evolution" is the incorporation of viral DNA/RNA into cells of higher life forms. In fact these higher life forms – mammals – have partially been created by the concept of "gene absorption" from a virus. Syncytin, a protein from a virus, has been demonstrated to have created the precursor for placenta cells, the very basic condition for the existence of mammals.
So, evolution may not only have made many small steps, induced by natural selection, but also may have taken quantum leaps by cell and gene absorption. For about 3 billion years, all organisms on Earth were microscopic, sometimes clogged together in a kind of slime. Complex organisms only appeared in the following 600 million years.
Life can survive and thrive in a wide range of conditions. On Earth, life has done extremely well, thanks to the very beneficial climatic conditions like temperature, humidity, geology, and a minimum of chemical and physical stress (acidity, oxidation, highly energetic rays, etc). If the concept of life does or did exist on other planets, it might not be similar to ours and not be so developed, but if we would find out that it does or did exist, then this would be far more meaningful than anything that we would have discovered until then.
The Secrecy of all Secrecies".
This small article about speculation on the origin of life might be challenging your beliefs and for some of you, maybe it is even shocking. By no means is this article a defamation of any thought, perception, logic or belief that anyone might have. On the contrary, although science is quite successful in providing answers to increasingly difficult questions, it will bump and bounce against the wall of the "Secrecy of all Secrecies"; about the origin of Matter, Energy, Space and even Time: "Where does this all come from?" or "What was before?" or "Who did create this?"
Source: Wikipedia, NASA