deletions | additions       diff --git a/Let_s_recap_we_are__.tex b/Let_s_recap_we_are__.tex  index 794da36..c0668c9 100644  --- a/Let_s_recap_we_are__.tex  +++ b/Let_s_recap_we_are__.tex 
...
Let's recap: we are thinking creatures living on planet orbiting a pretty common star. Our home planet has been around for about 4.5 billion years, while the Universe has about 13.7 billion years. We \href{https://www.authorea.com/10997}{just learned} that there are some other 1~000~000~000~000~000~000~000 = $10^{21}$ planets potentially similar to the Earth in the cosmos, a number larger that the \href{http://www.npr.org/blogs/krulwich/2012/09/17/161096233/which-is-greater-the-number-of-sand-grains-on-earth-or-stars-in-the-sky}{ grains of sand} found in every beach and every desert on Earth.\textbf{ Earth.\\  \textbf{  Are we alone?} alone?}\\  To answer this question the scientist Frank Drake came up with his famous equation in 1961, have a look at \href{https://www.authorea.com/11048}{previous post} to see what it looks like. This equation allows to calculate the number of communicative civilizations we might be able to contact.