It's "convenient" that we're the only planet in the Universe with life on it. Given there are trillions of planets out there.
Out of curiosity, how did you come to know we're the only planet with life on it? Not ONLY are there
So an average galaxy contains between 10^11 and 10^12 stars. In other words, galaxies, on average have between 100 billion and 1 trillion numbers of stars.
Now, how many galaxies are there? Astronomers estimate that there are approximately 100 billion to 1 trillion galaxies in the Universe. So if you multiply those two numbers together, you get between 10^22 and 10^24 stars in the Universe. How many stars? There are between 10 sextillion and 1 septillion stars in the Universe. That’s a large number of stars.
(source
http://www.universetoday.com/24328/how-many-stars/ )
...probably a lot more planets than a trillion, there is ALSO a lot more time than "now", so you can multiply that 10 sextillion (or up to a septillion) times
another 10 billion because this life could have happened 8 billion years
ago.
So given all those stars which might have planets, and all those years of past time as well as present,
I'm curious what made you conclude that you knew we were the only planet with life?
I think a better question to answer is how life actually came on Earth and how a single celled organism made life.
That is indeed a great question! An exciting one.
I've read several different ideas on how it could have happened using mechanisms that we understand. Any one of these
could describe what actually happened, and I wait with excitement as I read new experiments trying to demonstrate each theory to see if they can reproduce (if you'll pardon the pun) the event.
Several of these experiments have shown that the individual steps are quite possible. Excitement abounds as scientists continue the work. It's fascinating stuff!
You may enjoy reading at
Science News to browse articles on current science experiments. It's not an anti-religious, it's just straight science.