Are We Alone Research Paper

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Are we alone? Thoughts about astrobiology
There is life all around the planet, even in extreme habitats. How it is possible for organisms to survive in such extreme conditions? It is possible to have life out of Earth? How this life could be? To try answering these questions, it is necessary to look back to Earth’s history and its current environments and conditions, as well other places in the solar system, searching for tips in the complexity of organisms adapted to the extreme conditions for life beyond Earth.
Earth as known today is just temporally. The planet is always changing and once it was far different than it is now, it was an extreme habitat when life first appeared. The first fossil confirming life existence dates from 3.5 billion years ago [8]. However, the characteristics of this fossil indicate it was an organism reasonably evolved, suggesting that life appeared much prior in time. Even at present days is still hard to determine when the first life form appeared on Earth, since rocks older than approximately 3.5 Ga have been
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For instance, it was suggested that temperature in early Earth was higher than today, with an average of ocean water temperature above 50°C, proposing that life forms of this time should be tolerated elevated temperatures [8].
Although high/low temperature can be considerate an extreme condition, this is not the only factor that defines an extreme environment. It includes parameters such physical parameters (e.g., pressure, temperature and radiation) and geochemical parameters (e.g., pH and salinity). The natural or virtual arrangements of maximum or minimum values of these parameters (pH lower than 3, hydrostatic pressure above 20 MPa, temperature above 80°C, etc.), are challenging on development and survival of most life forms, denominate an extreme environment
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