Question

What were the odds that life would begin on earth?

Answer 1

1 in `10^40`

Explanation:

Depending on your source, and their assumptions, 1 in `10^40`.
ALL of these are conjectures based on assumptions, and sometimes questionable statistical applications. The values derived are for discussion. Do not use them as any sort of “fact”.

1 in 1 in `10^40`, http://evolutionfaq.com/articles/probability-life
This may be the most realistic in terms of basic “life” requirements without specifying higher organisms.

http://www.science20.com/news_releases/the_mathematical_probability_of_life_on_other_earth_like_planets
The chances of intelligent life emerging is low – less than 0.01 per cent over four billion years. We may be the only case, but imposes different conditions and a definition of intelligence rather than simply life.

One of the best general discussions (including the fact that he doesn’t indulge in statistical evaluations) is by Dr. Stephen Hawking, here:
http://www.hawking.org.uk/life-in-the-universe.html