Are Aliens Living Among Us?

pickens writes "In recent years scientists have begun to view the existence of life outside of our solar system as ever-more likely. If life does emerge readily under terrestrial conditions, then perhaps it formed many times on our home planet. To pursue this tantalizing possibility, scientists have begun searching deserts, lakes and caverns for evidence of earth-bound 'alien' life-forms, organisms that would differ fundamentally from all known living creatures because they arose independently. Microbes have already been found inhabiting extreme environments ranging from scalding volcanic vents to the dry valleys of Antarctica. Other so-called extremophiles can survive in salt-saturated lakes, highly acidic mine tailings contaminated with metals, and the waste pools of nuclear reactors. Although 'alien' microbes might look like ordinary bacteria, their biochemistry could involve exotic amino acids or different elemental building blocks so researchers are devising tests to identify exotic microbes. If shadow life is confined to the microbial realm, it is entirely possible that scientists have overlooked it."

Re:The odds aren't as poor as you think

[russ1337]

And I counter your offer with This [wikipedia.org]

Excerpt:

It is widely claimed that a common bacterium from the human mouth, Streptococcus mitis, survived for two and a half years on the Moon inside the Surveyor 3 camera, to be detected when the camera was returned to Earth on board the Apollo 12 capsule. However, this claim cannot be sustained in the light of several lines of evidence:
* Streptococcus mitis lives in the mouth; there is no evidence that it can survive for long even in terrestrial environments outside the human body.
* Streptococcus mitis, like other oral streptococci, is a mesophile; it cannot survive outside of a narrow temperature range centered on human body temperature. It is not an extremophile nor does it produce endospores. It could not survive on the moon.
* Even extremophiles are unlikely to survive the extremes of temperature on the surface of the Moon (mean surface temperature day 107C; mean surface temperature night -153). Surveyor 3 would have gone through over thirty day-night cycles on the Moon, each one provoking freeze-thawing of bacteria. Applying multiple cycles of freeze-thawing is a commonly used technique for breaking open bacterial cells.
* There is evidence to suggest ................(read the wikipedia article for the rest)

Re:I'm an alien, I'm a legal alien...

[Ralph Spoilsport]

Sting didn't write that. It's by Godley and Creme. The original is FUCKING BRILLIANT. G&C are awesome.

RS

Re:flip side

[keithius]

How about just "ugly bags of mostly water? [wikipedia.org]"

Re:this has already been shown!

[porpnorber]

Nah, mitochondria are like tapeworms (but more useful); they pass all the tests for being 'regular' life—they even have DNA. It's the fact that they do have their own DNA that's interesting, in fact; that's the strongest evidence for their having once been independent organisms. But we share a fairly recent common ancestor—they're just bacteria.

Re:this has already been shown!

[rizole]

A quick scan on wikipedia [wikipedia.org] and it looks like mitochondria are just symbiotic cells inside another cell and are basically made of the same stuff as you me and every other living thing including their own DNA. I'm simplifying horrendously here but I don't think you can assume life has evolved more than once because of mitochondria.