The reasoning is always as follows – if the earth were a little closer/further to the sun there would be no life. -Without the rotation of the earth there would be no magnetic field, without a magnetic field no protection against cosmic rays, life would not be possible without that shield. -etc. Plenty of reasoning that assumes that Earth is the ideal candidate for life to have. Makes sense given that so far we have only established evidence of life on this planet. However, Suppose I have a planet and on that planet it is full of minefields including associated signs. On this planet I plant simple life cells which follow evolution (we ignore the amount of time it takes for evolution for a moment) At some point we will get animals however many will die on the numerous minefields. At some point, an animal will associate the signs with not treading and thus gain an evolutionary advantage. Fast forward further in evolution and all animals susceptible to a mine will recognize the signs. If I reason in the same way, we would say, without the danger signs, no life is possible. While it is clear here that the reasoning goes the other way around, life has adapted to the circumstances. Replace the danger signs with a magnetic field and you can say that without that magnetic field evolution would simply have adapted to the higher radiation. Of course, to some extent, life has adapted to its environment through evolution. But the reasoning is always that the Earth is just perfect for life, and if you make even a small adjustment life could not exist. An unlikely opportunity really. Or suppose that life has adapted to its environment, a sudden change has catastrophic consequences because evolution takes time. Too big a change can mean the end of life.
Answer
We assume that the conditions on Earth make life possible. The main reason for this is that liquid water is present. Water is liquid between +0°C and about 90°C. Then there are possible chemical reactions that take place between substances that are soluble in water. And the chemical substances that can arise as a result are the basis of all life, namely the biomolecules from which all living things are built (nucleic acids, proteins, polysaccharides, phospholipids).
Conditions on our planet also changed at the hands of the living beings themselves. For example, originally there was no oxygen in the atmosphere. Oxygen was built up by photosynthetic unicellular organisms (cyanobacteria) and was initially toxic to the unicellular organisms living at the time. They had to adapt by developing chemical reactions to neutralize oxygen inside the cells. Later on, beings have evolved that need oxygen, etc. So, indeed, life does adapt well to changing conditions through the process of evolution.
Will a small adjustment make life impossible? That is indeed unlikely. But our planet has long had a formidable biodiversity. Meanwhile, many animal and plant species have become extinct in a short time due to human activity (on a much smaller time scale than was the case with earlier extinction periods). If this continues, biodiversity, the diversity of species, will continue to decline drastically. A lot of time is needed for new species to evolve. So if the changes are going too fast, it won’t be possible. Except for organisms with a very short life cycle, which can evolve much faster, such as bacteria.
The complete disappearance of all life on our planet, including single-celled organisms such as bacteria, may only occur if all the water on the planet is either frozen or evaporated.
Answered by
Prof. dr. dr. Luc Bouwens
Biomedical Sciences
Avenue de la Plein 2 1050 Ixelles
http://www.vub.ac.be/
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