Life did not suddenly come together like a tornado in a scrap heap. It also does not appear when you try all possible options before choosing the best one. All life arose on this rock floating in space beneath our feet through the slow, meandering trial-and-error method (which might perhaps be better called trial-and-error) by which evolution has occurred on Earth for the past four billion years. .
By the way, we’re not the only space rock in existence. There are eight planets in our solar system (until recently nine, until poor Pluto was demoted in 2006), as well as a number of dwarf planets (of which Pluto is now one) and hundreds of moons. Although the number of potential candidates for a celestial place to harbor life is very limited due to some specific conditions – liquid, atmosphere, protection from solar radiation – there are still some interesting contenders among them. Titan – Saturn’s largest moon – has a thick, nitrogen-rich atmosphere, complete with cirrus clouds and seasonal storms (although the rain is gasoline and the snow is pure soot). Ganymede – Jupiter’s largest moon – has a core of liquid iron orbiting around it, creating a magnetic field (Earth’s magnetic field forms a shield against the sun’s bright rays, which would otherwise destroy every bit of DNA and incinerate every living thing). Europa – another satellite of Jupiter – has an ocean of liquid water just below the surface, rich in salts and other components that have turned chemistry into our world’s biochemistry.
Bacteria have been around since the beginning of life and will continue to exist until the end of life on Earth, long after we become extinct
There are more candidates outside our little corner of the universe. The first exoplanets – planets outside our solar system – were discovered in the 1990s, and thousands more have been confirmed since then. Millions more are still waiting for classification. The Earth may be full of life, but the universe is full of planets.
It is impossible to calculate the probability of extraterrestrial life, because so far we have only taken a small sample of the universe. This is a question with only two possible answers: either there is life elsewhere in the universe, or we are alone. From a scientific point of view, this is a win-win situation: both answers are equally astonishing.
Most life on Earth consists of bacteria, small single-celled organisms that outnumber and mass more than any other life form. They are even more numerous on our bodies; We all host much larger numbers of bacterial cells than our human cells. Since they are much smaller than our cells, we are still very much human in terms of mass, but in numbers we are largely something else. Bacteria have been around since the beginning of life, and will continue to exist until the end of life on Earth, long after we become extinct. Given the dominance of bacteria, we think that these simpler life forms are good models for extraterrestrial life, but although we have great respect for bacterial life on Earth – and, more importantly, we are completely dependent on it – we have to admit that they are quite boring. Especially to look at, because they are too small to see.
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