While the possibility for life is hugely likely, given the immense time and enormous quantity of planets, the evolution of intelligence is another matter. That requires even greater overcoming of limitations. Intelligence requires sophisticated cells. The development of such sophistication is an immensely unlikely event on a par with that of the formation and incorporation of DNA.
On this planet the incorporation of DNA took place early on when the Earth had cooled and conditions were right. The formation of Eukaryotic cells (sophisticated cells that would support complex multi-celled life) requires two incredible occurrences. Firstly they have to incorporate or evolve cellular powerhouses to provide energy. On Earth this happened when bacteria (that were mitochondria-like) became symbiotically incorporated into cells. Secondly they have to have incorporated chlorophyll-rich chloroplasts to break down water to release oxygen and produce food.
The plants incorporated chlorophyll rich bacteria symbiotically. In so doing they changed the atmosphere of the planet and the oxygen enabled life to become more complex.
These two limiting factors are incredibly difficult leaps.
Not only do planets have to be in the ‘Goldilocks Zone’ and have given rise to life that incorporates DNA (or its equivalent) but it would also have to evolve through these two other immensely difficult bottle-necks in order to achieve the complexity necessary for intelligence.
The consensus is that this will only occur on an incredibly small number of occasions.
Fortunately – with the zillions of planets out there and the colossal periods of time involved even the most unlikely events will occur. That is what is so incredibly awesome.
All things are possible given enough time and an almost infinite system.
There are probably billions of planets on which life will have occurred and there are likely to be hundreds of thousands of planets out there supporting intelligent life!
Which is more scary? Having a universe with other intelligent life or that we are the only ones?
If there is intelligence out there! How do we contact it?