Most scientists think that there is a high probability that life exists somewhere else in the universe because there are so many galaxies (billions), and each galaxy may contain billions of stars. Therefore there is no reason to believe that earth is the only place in the entire universe suitable for the evolution...
Best answer: Most scientists think that there is a high probability that life exists somewhere else in the universe because there are so many galaxies (billions), and each galaxy may contain billions of stars. Therefore there is no reason to believe that earth is the only place in the entire universe suitable for the evolution of life and the only place in which life evolved from inorganic substances. We find amino acids, one of the building blocks of life, in meteors. The condition of the early earth favored the synthesis of organic compounds including protein. Similar conditions elsewhere on another planet in another solar system would probably result in the evolution of life.
However, since science relies on evidence, all scientists would agree that there is as yet no evidence of life outside of planet earth. It does not mean that there isn't any extraterrestrial life, but we simply have not found evidence of it yet, so we cannot say that there is extraterrestrial life either, regardless of how likely it may be. A few decades ago, there was no evidence that planets are found outside of our solar system, although scientists also reasoned that they almost certainly existed elsewhere in the universe. Now we have tons of evidence of other planets elsewhere because of new telescopes and new techniques designed to find them. Life, however, may be much harder to detect because even on our own planet, life only existed as single-celled, microscopic organisms for almost 3 billion years before the first multi-cellular organisms evolved. The only way to find them would be to have a physical sample of another planet and look through microscopes. Since the nearest star is too far for us to go to, it would therefore be impossible to sample other planets physically for evidence of microscopic life.
Only within the past 100 years or so did we invent radio waves to send signals outside of our planet, and humans have evolved 150,000-200,000 years ago. Therefore even if intelligent life were to exist elsewhere in the universe, they may be pretty rare and even rarer are life forms that knows how to send radio waves. Therefore it would be extremely difficult to find them. Therefore we will probably not know within our lifetime whether extraterrestrial life exists or not, even though some scientists are spending time searching for radio waves that may have been sent out by intelligent life elsewhere. Even more improbable are space aliens that are technologically so advanced that they traveled to our planet, not withstanding all those UFO stories.