Until today, Earth is the only known place where life has evolved. It is very likely that there is life in many other corners of the Cosmos. But would we know how to recognize it? Will it be similar to ours?
Perhaps there are ways of life very different from what we imagine. Even on Earth, biodiversity is very broad. From the simplest microorganism to the complexity of the human being, through plants, fish, insects, reptiles, birds, mammals ... Everything is life. It takes very different forms, but they always have something in common: all life on Earth is based on carbon chemistry, and it needs liquid water.
We assume that these requirements are necessary for any kind of life in the universe. But it may not be so. The science that studies what life on Earth can be like is called exobiology or astrobiology.
In Nature there are 92 chemical elements, which form all known matter, including living things. So any kind of life will be a combination of these elements. But can there be life without the support of an organic chemistry? That is, can there be life without matter? For example, life formed by electric or magnetic currents, plasma flows, etc.
Fred Hoyle's novel "The Black Cloud" raises the hypothesis of an interstellar cloud that comes alive. The organic molecules in the cloud remain bound by gravity and begin to interact as a single organism. It is only science fiction, but forces the question to be asked: what do we understand by life?
The limit is not clear. There is not even agreement on whether viruses are living beings or not. At the moment, Hoyle's example does not seem possible. Life needs matter, formed by organic chemistry. And the minimum requirement is that you have genetic information that can be transmitted when reproduced.
Once life appears, it evolves. It adapts to the conditions of the environment to survive. Biological evolution does not follow the same laws throughout the universe, but depends on the environment. Thus, in different environments, the evolution will be different.
Carl Sagan gives an example of the evolution of life on a gaseous planet. Life was born on Earth and adapted to its rocky environment. We could not live in another environment. But if life appeared on a gaseous planet, it would evolve differently. The physical and chemical laws would be the same as for us. But its evolution would produce very different ways of life. For example, there might be floating creatures, which are driven by gases. There would be different types of life, specialized in surviving in the different layers of the atmosphere.
Extremophiles are proof that life can exist under very different conditions. The laws of nature are universal, but evolution can take unimaginable forms. If we found life very different from ours, would we recognize it?
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