I would be very surprised if the earth contained the only life in the universe. This is a list of the primary reasons why I think extraterrestrial life is likely.

1.The Miller-Urey Experiment and Joan Oro

The sheer ease with which the building blocks of life can be created, makes it easy to imagine life being created on other planets. Stanley Miller and Harold Urey were able to create 13 of the 22 amino acids that make up life. This was done by adding electricity to gases that were probably floating around in the atmosphere during early earth. Later on Joan Oro was able to create the nucleotide base adenine with water, HCN, and ammonia. Since then many other experimenters have successfully produced other DNA and RNA bases using similar experiments. While these RNA bases do not replicate, it would not be hard to imagine them forming something that could replicate. It would only have to happen once because… it would be replicating.

2. Our energy source, the sun, isn’t special.

In fact our sun is pretty much as average as you can get. It’s average sized, and average aged, and made of the typical materials believed to be found in most other stars.

3. There are other planets that can probably support earth-like life.

The earth is more unique than the sun, but there are probably many planets that are similar to earth. It is a small, rocky planet; Jupiter-like planets seem to be the norm in the universe. Even more unique is the abundance of water that is continuously in liquid form. For this to happen a planet must be kept in a narrow temperature range. We also have a moon that stabilizes our spin so that we do not have huge climate changes. Despite these unique factors, we are already finding planets that might be able to support life, and we haven’t even studied a speck of the universe.

4. Life might be able to form under conditions completely different from earth’s. This would make life on other planets even more likely.

Links:

There Are Other Lifeforms This shows drawings created by ancient cultures, that might be pictures of aliens and UFOs. This article also discusses statistics about who does and does not believe in aliens.

Earth-like Planets This article explains how earth-like planets are being searched for based on wavelengths.