I'm okay with the Field of Dreams interpretation of astrobiology: "If you build it, they will come", so to speak. All you need is for life to take hold once and it'll take over a planet in just a few billion years. Of course, my own hunch is that suitable chunks of rock (planets, moons, etc) are somewhat more rare than the default value[1].
[1] I plugged in .1, among other variable changes. On the other hand, I got the number of communicating civilizations = .02, so either I'm too pessimistic or we're just really, really lucky.
I think there are far too many happen chances in evolutionary biology to say that an advanced civilization is inevitable; my rational mind has a LOT of trouble accepting that our current development is a long history of happen-stances beginning from life´s first development, but I see no viable alternative. But to think that given another Earth with life it would happen again? With all of the stretches that happen all along the evolutionary tree I find this absurd.
I concur. Fortunately, the Drake equation gives us separate variables for "develops life" and "develops intelligent life". The value I used for f_i was somewhat lower than they gave, but I also thought that f_c was higher, so it worked out as a wash.
Actually the only thing we know for sure is that life on Earth happened at least once. It is entirely conceivable that several alternatives to RNA-based life (precursor to DNA-based life) popped up in several different places but then were hopelessly out-competed by the RNA-based lifeforms. I am a biologist by training, and the more I studied biology and evolution, the more life appeared to me as a powerful (somewhat scary even) and inevitable process, rather than a "unique snowflake" that many of us commonly think it to be.
Life, given right conditions and enough time, seems to be about as inevitable as the eventual appearance of viral cat pictures on online forums, in other words.
I think there is little wrong with assuming that the probability of emergence of life given right conditions and enough time is one; however we need to be very careful with estimating how common (and how stable!) those conditions are in our galaxy in the first place. A good place to start would be to look at how many places similar to Earth are out there (which we are already doing).
I think there is little wrong with assuming that the probability of appearance of life given right condition and time to develop is one
Fair enough. It's a bit like the infinite monkeys in infinite typewriters scenario. Given enough time, sure, you'll have life. It's a question of how much time. Still, assuming all Eart-like planets will actually develop life given the time lapse of the existence of the Milky Way does still seems like a bold assumption.
I am not a geologist, but the Wikipedia article on the Late Heavy Bombardment (http://en.wikipedia.org/wiki/Late_Heavy_Bombardment#Geologic...) says that 100 million years is the time that an Earth-sized body would take to to cool down and form a crust (the bombardment basically tuned the Earth into a ball of molten magma).
I assume "Earth like" in this context means planets that resemble the only planet known to hold life at least enough to be capable of holding life themselves. The problem is we don't even know what that means exactly. It's also assuming that life can only exist in "Earth like" conditions.
Also, if Fraction of Earth‐like planets that develop life = 1 and Mars is an "Earth like" planet, are they assuming life evolved in Mars too or something?
in that case, value of 1 for "fraction of Earth‐like planets that develop life" is odd since we are far from confident that life ever developed on mars.
What we call atmosphere in Mars would pass for a very good vacuum in a classroom. Life could develop on a Mars sized body, but then the star would have to be far less active than our sun (so that the planet could retain a reasonable atmosphere)
