A Question For Everyone: Is the truth out there?
The discovery of extra-terrestrial life would be something that would change all our lives forever. Actually seeing life from a different planet would be something that would, no doubt, terrify, shock, excite, and intrigue us like nothing else could. But then again, what are the chances of finding it?
There are various factors any hypothetical life-form would need to overcome in order for life to start. Developing is a whole other issue all together (as the universe is an ever-evolving place).
The "Rare Earth" hypothesis puts forth the notion that life like our own may be a very rare (if not singular), occurrence throughout all of time and space.
Why Life *Might* Be Rare:
The planet or moon (perhaps a number of moons orbiting other planets hold the potential for life) would need to be at the ideal distance from its parent star, this is called the habitable zone. Also, the star itself must meet a stringent list of requirements. It would need to be the right size and luminosity to help support the life as it evolves. It would also need to have the right sort of atmosphere and temperature, so that water wouldn't boil or freeze over. (On this note, a stabilized orbit is also a necessity. If the planet veers too far off course, the temperatures would be all over the place, which again, isn't conductive to life)
The habitable planet would benefit from having a gas-giant like Jupiter nearby to knock any potential harmful meteors off-course. It would need to have the right size, mass, axial tilt and rotational speed to have ideal exposure for photosynthesis and the right gravitational pull.
It would need to be in the galactic habitable zone, so it would need to be far enough from the heavily populated galactic center - or an other highly-populated area, for that matter - to avoid any collisions, or to prevent the planet from being bombarded with gamma radiation streaming from exploding stars, or from the outbursts of a central black hole.
Taking all this into consideration, when I was first reading about the "Rare Earth" hypothesis my hope started to fade a little as it dawned on me that the checklist is quite demanding for a planet to be given even the most remote consideration of it potentially harboring life like ours.
Having said that, these are only ideal conditions for us as we are now. This seems to put aside a massive part of evolution:
Over millions of years, species have evolved to adapt to their environment. We have fish and other exotic forms of life that can survive under immense pressures within the deepest depths on the ocean floor. We have algae that can survive in boiling temperatures. Then, we have the lovely tardigrades (also known as water bears), which can survive IN THE VACUUM OF SPACE.
So life could thrive in environments much different than that of our own blue marble. On top of this, there are more and more Earth-like exoplanets being discovered each day, just within our galaxy alone. This doesn't necessarily mean that Earth-like life has a fighting chance on any of them, but it also doesn't mean that there never will be!
The Principle of Mediocrity suggests that there is nothing special about us whatsoever, there's nothing uncommon about our particular position... to think that there isn't life in the depths of the cosmos would be crazy.
On a final note:
This article is merely meant to spike a sense of wonder, not to encourage you to wear tin foil hats and have Mulder and Scully on speed-dial!
"The human race is just a chemical scum on a moderate-sized planet, orbiting around a very average star in the outer suburb of one among a hundred billion galaxies."
~ Stephen Hawking