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Earth-Like Planets In Our Neighborhood
goran72 sends in a story out of the Chicago AAAS meeting contending that Earth-like planets with life-sustaining conditions may be spinning around stars in our galactic neighborhood — we just haven't found them yet. "'So I think there is a very good chance that we will find some Earth-like planets within 10, 20 or 30 light years of the Sun,' astrophysicist [Alan Boss]... told his AAAS colleagues meeting here since Thursday. ... The images from those new planets, he added, should identify 'light from their atmosphere and tell us if they have perhaps methane and oxygen. That will be pretty strong proof they are not only habitable but actually are inhabited. I am not talking about a planet with intelligence on it. I simply say if you have a habitable world. ... Sitting there, with the right temperature with water for a billion years, something is going to come out of it. At least we will have microbes,' said Boss."
The human body contains about 100g of DNA. You're saying about 2E15 grams, or 20 trillion human body's worth, of DNA is not only released into the atmosphere but then escapes the earths gravitational pull and enters interplanetary space.
Sounds unlikely.
... exchange communication once every 10 years,...
We could give them, say, the entirety of Wikipedia, and they could give us their equivalent. Write up a "rosetta stone" with a bunch of pictorial/mathematical representations of words, and so on. Probably doable. Conversation back and forth will seem frustratingly slow, but there's no limit to the amount of info that can be streamed across.
Mind you the chances that we will be in the near vicinity of a civilization that communicates by radio waves that we can pick up is possibly quite slim- we've only been doing it for less than a hundred years. They could be in our equivalent of 1750 and we'd never hear a peep.
I would think that we wouldn't just send "Hi" and wait for a response. I think we would constantly be sending them information and let them learn what we are sending. We would hope they would do something similar.
All right, What The Hell?
For a planet to "shed" anything except perhaps hydrogen or helium, that stuff has to overcome escape velocity, which (until rockets were invented in the 20th century), requires an (volcano or meteorite) that would incinerate any complex organic compounds and render DNA a fine ash.
Plus, Google will tell you that the following comes out to 44%, as an above poster already said:
(4 billion years) * (2 billion tons per day) / (5.9736Ã--10^24 kg) in percent
Less than 1% of Earth's mass is at a temperature that even permits life to exist. As for the part that actually consists of life, you can measure it in parts per million and still need scientific notation.
From scarped cliff or quarried stone she cries "A thousand types are gone, I care for nothing, no not one."
we have no reason to suspect that there is life beyond this planet.
No reason to suspect? It goes like this. There is life on this planet. Therefore probability of life > 0. There are many, many, many stars in our galaxy, countless in the universe. No matter how small the chances are, given the size of the universe and since we have proven that the probability is greater than 0, it's inconceivable to imagine that we're the only ones.
In fact, the only reason to be arrogant enough to say that we're the only ones would be religious nonsense.