deletions | additions       diff --git a/Astrobiology.tex b/Astrobiology.tex  index 3fea4ec..ea68285 100644  --- a/Astrobiology.tex  +++ b/Astrobiology.tex 
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%cradles for life as we know it are common in the universe or Next step is characterizing these worlds, and finding %trace of life.   $f_l$ \textbf{How likely is the emergence of life}?   If life was impossible nobody would know about it. Similarly Similarly,  the fact that we exist see life  on Earth can not be used to draw conclusions on how probable this  islife  in the Universe. Think about it: Even if this probability Universe\footnote{If Earth  was extremely low and life existed the  only on one life-hosting  planet in the Universe, who's asking the question has cosmos, we would  necessarily have  to be on that planet.   The cool thing is that, statistically speaking, living there}.  However,  finding just another place outside the Earth  where life can be supported changes everything. Finding traces of life (even fossil) on Mars or on one of the moons of Saturn or Jupiter would demonstrate that the emergence of life (biogenesis) does not require a very narrow, unlikely set of conditions. \\ For Until that moment, and I strongly believe we'll see proof of  the time being existence of life in other regions of the solar system very soon,  an interesting argument that is used to constrain $f_l$ is the rapidity of biogenesis on Earth. That is how long it took for life to emerge once the conditions at the surface of our planet were "stable" enough. The argument is the following: imaginethis as  a lottery with life as  first prize being the appearence of life. Now if prize. If  the emergence of life is a  very unlikely outcome (requiring very specific conditions), then to win the lottery one has to play many times, just because the winning ticket is one out of very  many. If on the other hand winning the lottery is relatively easy (many winning tickets, or if you want many different combinations of the environmental conditions can lead to life) one needs to play just a few times before winning. It turns out that biogenesis on Earth was fairly rapid compared to geological times. Using a conservative upper limit of 600 million years required by life to emerge once the conditions were "stable enough", constrains the probability of biogenesis in terrestrial planets older than 1 billion years to be greater than $13\%$ \cite{Lineweaver_Davis_2002}. That is to say about 1 in 10 Earth-like planets in the habitable zone should develop life. $f_l \ge 0.13$ \\ %Having one data point, the Earth, doesn't give any statistical information: the solar system could well be an extremely %unlikely, or even unique, place in the Universe. As soon as you ask the question "Are we alone?" it means you are alive %and conscious, i.e. you are in a sweet-spot, and you can not make any claim about how common that might be. Beside the fact that one such place exists.