Are alien lifeforms already on Earth?

Paul Raven @ 21-11-2007

A cluster of Escherichia coli bacteria Is the emergence of life a localised one-shot fluke, or does it happen all over the place? It’s not a question we can answer with certainty yet, but that’s probably why it’s such a fascinating thing to ponder. Scientists in the latter camp suggest that life may have arisen here on Earth more than once, and according to Scientific American they are engaged in a search for examples of Terran microbial lifeforms which aren’t (or rather weren’t) based on the building blocks of the biology that we’re more accustomed to – which might add evidence in favour of the emergence of extra-terrestrial life. [Via Slashdot] [Image from Wikipedia]

Of course, some of the creatures that have existed on Earth that were based on the familiar biological patterns can still seem pretty alien, if only in the B-movie/pulp magazine manner – 2.5 meter long monster sea scorpion, anyone?

[tags]life, biology, science, extraterrestrial[/tags]
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One Response to “Are alien lifeforms already on Earth?”

  1. Phil says:

    A couple of interesting points from the article:

    (1) “…it was a bacterium with the surprising ability to chemically alter the amino acids and sugars of the wrong handedness so as to make them digestible.”

    This strongly suggests that the bacterium regularly encounters molecules of the wrong-handedness, but all known life produces molecules of the correct handedness. If there were a lot of the “wrong” molecules hanging around out there, then these conversion enzymes would be very common in bacteria. So where are the wrong molecules coming from?

    (2) “The Murchison meteorite, a cometary remnant that fell in Australia in 1969, contained many common amino acids but also some unusual ones, such as isovaline and pseudoleucine. (Scientists are not sure how the amino acids formed in the meteorite, but most researchers believe that the chemicals were not produced by biological activity.)”

    Complex organic compounds travel through space on rocks and crash onto planets. Should such a rock crash onto a primordial Earth-like planet, it could kickstart “life.” Thus there’s a good chance that life is common in the universe.