Life in the Universe part 4: On how many planets will life arise?

This is part of the Life in the Universe series of posts. Go here for the first one.

Don't know who to attribute this to... click for original
Part 3 discussed possibilities for the fraction of existing planets on which the conditions would at some point in their existence be suitable for life to develop. Now we need to look at the probability of life actually popping up on any one of these planets should such conditions exist.

Looking at our own planet, which so far provides us with the only information we have with regards to life, we see that the first living things appeared on Earth around 3.8 billion* years ago, which is very soon after conditions became suitable. Assuming that our circumstances are not in some way special** it seems that, given the right conditions, life finds it quite easy to get started: If it were particularly difficult, it would probably have taken longer to take hold.

So life, as Dr Ian Malcolm says in Jurassic Park, finds a way. Or at least it appears so from our admittedly limited data. So can this post be the first in which we are truly optimistic about the chances of life cropping up elsewhere in the universe? If so, it would not be wildly speculative to suggest that, given the right location and conditions, the chances of life arising may be close to, if not actually, 100%. That would mean that in the right place, with the right amounts and mixtures of heat, light and certain chemical elements***, life has to crop up, for reasons we haven't yet figured out.



Life in the Universe
This is the fourth in a series of posts about Life in the Universe, culminating in a discussion about the Drake Equation. The first post concentrated on the number of suitable stars formed each year. The next one will follow on from this one and discuss how many of these life-nurturing planets will see the development of intelligence.






* That's nine zeroes.
** A sensible assumption to make without further information to go on: why would things necessarily be different here than elsewhere?
*** That is, all of the planets that fit into the criteria discussed in the previous post in this series.

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