deletions | additions       diff --git a/Life Emergence.tex b/Life Emergence.tex  index c50621a..345e560 100644  --- a/Life Emergence.tex  +++ b/Life Emergence.tex 
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One of the most important factors in the equation is $f_l$, the fraction of Earth-like planets in the habitable zone that develop life. It is a measure of the likelihood of \textbf{life emergence}.  Here I will not won't  get into the interesting but complex debate about the definition of "life". Instead I will use an operative, somewhat restrictive definition: "life as we know it", loosely it". Loosely  meaning anything similar to what we've seen on Earth. One has to start somewhere. How can we estimate the likelihood of life emergence? If life was impossible impossible,  nobody would know about it. Similarly, the fact that we see life on Earth can not be used to draw conclusions on how widespreadis  life is  in the Universe, since Universe;  if Earth was were  the only life-hosting planet in the cosmos, we would necessarilyhave to  be living there. However, finding just another place outsidethe  Earth where life can be supported changes everything. Evidence of life (even fossil) on Mars or on one of the moons a moon  of Saturn or Jupiter would demonstrate that the emergence of life (biogenesis) does not require a very narrow, unlikely set of conditions. I strongly believe we'll see proof of the existence of life in other regions of the solar system very soon. Until that moment moment,  an interesting argumentthat is  used to constrain $f_l$ is the rapidity of biogenesis on Earth. The argument It  is the following: imagine a lottery with life as first prize. If the emergence of life is a very unlikely \textbf{very unlikely}  outcome (requiring very specific conditions), then to win the lottery one \textbf{one  has to play many times, just because times} to get  the winning ticket is one out of very many. ticket.  If on the other hand winning the lottery is relatively easy (many (either many  winning tickets, orif you want  many different combinations ofthe  environmental conditionscan  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. geologic timescales.  Using a conservative upper limit of 600 million years required by life to emerge once the for  conditions were to be  "stable enough", constrains enough" for life to emerge,  the probability of biogenesis in on  terrestrial (Earth-like)  planets is constrained to those  older than 1 billion years to be years,  greater than $13\%$ \cite{Lineweaver_Davis_2002}. That is to say is,  about 1 in 10 Earth-like planets in the habitable zone should develop life. \begin{quote}  $f_l \ge 0.13$ \\ \end{quote}\\  I am pretty confident life as we know it is widespread in the Universe: Microbial life is likely present in several places in our solar system as well as in a large fraction of the billions of planets in the cosmos.