Listing the Things Neccessary for Human Life As We Know It on A Planet

If it also had Dinosaurs then the tiny mammals that evolve into being human beings would also need to have the planet hit by an asteroid to wipe out these larger LIFE FORMS so that the mammals could then proceed to become what we've become.

The STAR would also need to be a MIDDLE AGED Star like ours if the planet is also located in the GOLDILOCKS Zone, because in a couple of Billion years our STAR will also begin to grow into it's RED GIANT phase which means the temperature will rise and begin to boil away our oceans.

So the AGE of the STAR would also be an issue.

And this other planet in the Goldilocks zone would also need to be HIT just right ... and in the SAME PLACE as another PROTO PLANET hit us ... in order to form another moon like our moon.

And it would also need another GAS GIANT with GRAVITY like JUPITER ... our COSMIC HOOVER ... that SUCKS up most of the comets and other asteroids before they can make it into the center part of our Solar System and hit us.

Seems like there's just too many VARIABLES INVOLVED with the process needed for life forms like ours to exist on a planet.

And even IF a planet would have EXACTLY the same set of situations, there would also be the TIME FACTOR, which means our life form may also NOT EXIST at the same time as it would on another planet LIKE OURS in another SOLAR SYSTEM like ours, with a STAR the same size and age as ours, etc.

And the search for another EARTH like planet is also showing us how the arrangement of our planet in our SOLAR SYSTEM is also definitely NOT THE NORM.

Most STARS are also RED DWARFS and not STARS like our STAR.

Something like 70% of them are RED DWARFS.

So that also narrows things down a bit when it comes to finding a duplicate solar system and planet like ours.

Here's a couple more for your list:

FREE OXYGEN: The planet should definitely have some sort of process (e.g., stromatolites or other primitive life) that can produce atmospheric oxygen from the various oxides on the surface and/or in the oceans, since oxygen, when left to its own devices, likes to combine with things (e.g., rusting any exposed iron). This isn't just for breathing; even with a magnetic field, a planet still needs an ozone layer or something like it to keep the sun's UV radiation from frying whatever is wandering around on dry land.

IT MUST ORBIT A RELATIVELY MASSIVE SUN. If the sun is too small, e.g., a red dwarf, it will definitely live for a long, long, long time, but it will be so cool in temperature that the planet would have to be so close to the sun that it would be tidally locked, like our moon is to Earth, so one side is perpetually hot and the other side is in eternal frozen night.

- Weather/water cycle
- an appreciable atmosphere with a significant greenhouse gas effect (but not one that is too strong, or the planet may become hellish like Venus)
- An elliptical orbit(but not so elliptical that it takes the planet too far away from, or too close to, its star)
- metallicity/metal content in the star (with out it, the likelihood of terrestrial planets developing decreases)
- A gas giant must be located further out, instead of in the inner solar system (we don't want a gas giant hogging up the habitable zone)

Cram it with walnuts, ugly!

A very interesting topic, this! It seems to me that many don't fully appreciate what an amazing coincidence it is that we exist at all, even on a planet seemingly perfect for life, like our own Earth.

It might just be that life in its simplest form comes into existence quite easily, but how probable is multicellular life at all, let alone life forms with vertebrae, let alone mammals, LET ALONE humanoids? After all, even this planet went through almost four billion years of dullness before the Cambric explosion were to happen.

About the pretty unlikely chain of events that led to us, I highly recommend this: http://www.amazon.com/Rare-Earth-Complex-Uncommon-Universe/dp/0387952896

You might not agree with the writers' hypothesis, but nonetheless it's a fascinating and highly enlightening read.


Don't breathe air. Birds *beep* in it!