Origins of Life
How and when life began on Earth, we do not know. Researchers believe that the beginning of life has been about 3.5 billion years ago in the deep sea. Here maybe the first organic compounds have been formed, from which single-celled organisms developed, and then more complex creatures emerged. According to other theories, also comets could have brought life to Earth. (Source: image and text wikipedia)
Conditions for life in the universe
Searching for other earthlike planets, the orbit of the planet is interesting. The orbit must be a circle around the sun to ensure same conditions for life throughout the year. Life as we know can develop on rocky planets.
Applies to the development of an eco-sphere:
Planet: liquid water must be stable. It must have enough mass to hold an atmosphere and oceans.
Sun: must have long life so that life can arise, not too much UV light may strike the surface of the planet.
Orbits: Gas giants may not cause chaos, their orbits should not be too eccentric. (Source: Dagmar Röhrlich - Hello, anybody out there? Spectrum Verlag 2009)
State of research
That there is intelligent life beyond Earth particularly you can conlude from the facts stated that only in the Milky Way there are 200 to 400
billions of stars, and this is just one of more than 100 billion galaxies. Furthermore our sun has no special features on planetary systems and also appears to be widespread. Thus, researchers suppose that there are many planets that offer similarly good conditions for life like our earth.
This is disregarded, however, because the time window of intelligent life perhaps is only a few million years. (Source: wikipedia)
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