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There is no solid evidence for the existence of life of any kind, let alone intelligent life, anywhere other than on Earth.
This is not for lack of looking, however. In 1952, Stanley Miller and Harold Urey attempted to simulate the early Earth’s environment within a sealed container. They combined water (for oceans), methane, ammonia, and hydrogen (like Earth’s early atmosphere), and an electric arc (for lightning bolts). They let the sparks operate for a week, then analyzed the contents.
They found amino acids (the building blocks of protein), some fatty acids and urea, all important chemicals for life-processes.
Further experimentation has shown that the same chemicals can be formed using different combinations of initial chemicals and energy sources.
This suggests that life is not uncommon in the Universe, since the important chemicals are not uncommon.
One way that scientists are looking for intelligent life is by looking for radio signals, usually referred to as SETI, the Search for Extra-Terrestrial Intelligence. In our galaxy, there are roughly 100 billion stars.
Even if only one percent of these could last long enough for life to evolve, and even if only one percent had planets that contained water, that’s still at least 100 million potentially life-bearing planets.
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