Here's how you know it's a small number, <br>the earth is 4.5B years old and humans with critical thinking skills took 4.49B years to show up... <br>We are only 1 of billions or trillions of species that have lived (if you count ALL life forms, including microorganisms) <br><br>...so this means that life begins with simple organisms , most likely, and it takes billions of years........<br><br>Something tells me there are many civilizations out there but they are in  different galaxies