[ugh]

Wikipedia has a helpful timeline of life on Earth: http://en.wikipedia.org/wiki/Timeline_of_evolution#Basic_tim...

You would most likely meet completely unintelligent microbes on Earth. Or no life at all. Maybe some stupid animals or plants.

The likelihood of meeting intelligent life during the existence of this planet is something like 0.004 percent (200,000 years of intelligent life on a 4.5 billion year old planet), the likelihood of meeting nothing but microbes is greater than fifty percent. It’s consequently only reasonable to expect most alien life to be microbes.

Older intelligent civilizations could certainly exist on older planets but the age of the universe is only 14 billion years. If the average planet is something like 7 billion years old (based on the naive assumption that planets form at a constant rate) then it is only reasonable to expect that most intelligent life out there existed for no longer than something like 2.5 billion years. Oh, and past mass extinctions on Earth cast serious doubt on the ability of complex life to survive for very long. Microbes, on the other hand, are undisturbed by asteroids and volcanoes.

That’s not human arrogance. That’s just how it looks to be at the moment.

Should we find an Earth-like planet sometime in the future and detect oxygen in its atmosphere I would expect to meet microbes, not intelligent beings. (We will certainly be able to detect Earth-like planets very soon and we might even be able to detect whether those planets have oxygen but we will probably never be able to actually go there so this point is kind of moot.)

[moe]

That’s not human arrogance. That’s just how it looks to be at the moment.

Human arrogance I say (and that is not aimed at you personally).

We're making assumptions based on a ridiculously small and sparse amount of knowledge. We assume the universe is 14 billion years old, we assume other lifeforms are carbon based like us and evolve the same way we do, we assume faster-than-light travel is not possible.

I don't see how this is any different to how we assumed the earth is flat, just a few hundred years ago.

In the grand scheme of things we simply don't know enough to make anything but the wildest guesses about alien intelligent life. Considering ourselves to be the pinnacle of evolution at this point seems very naive.

[manicbovine]

It's much different from assuming a flat earth. There has always been good and readily available data supporting the hypothesis of a non-flat earth. Various cultures have used this data to realize that the earth is not flat.

Our dataset about life is ostensibly limited to earth-based life. If we abandon available data, we are limited to making wild untestable conjectures.

What is the alternative? Should we just stop thinking about it?

[ugh]

Nobody assumes that humans are any kind of pinnacle of evolution. I never said that, the submission never said that. There is a difference between “most life out there is probably microbes” and “all life except for life on Earth is microbes”.

It’s a wild guess (astrophysicists would take exception, however, with the assertion that they got the age of the universe wrong) but it’s also the best we have. And there is nothing wrong with that and it is not arrogance.

[nandemo]

> Wikipedia has a helpful timeline of life on Earth:

Err, I had no idea that flowers appeared later than mammals and birds. Is that a well-known fact that I should've learned in high school?

[ugh]

Flowers are complicated, their late arrival is not really surprising. 130 million years is also not exactly recent. It’s not like some cavemen lived in a world without flowers.