So....I am always thinking that it is so amazing that with the universe being so big, how can We (humans) be the only possible lifeforms in the universe, much less the only intelligent sentient forms of life here on earth??
A story I read just a minute ago put fourth an interesting concept. Hmmm....
I have copied the story here (in it's entirety) for everyone's viewing pleasure....
Happy Tuesday
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Goodbye Mars, Hello Earth
By PAUL DAVIES
Sydney
WHEN I was a student in the 1960's, anyone who believed that there might be life on other planets was considered a crackpot. Now all that has changed. To claim that life is widespread in the universe is not only respectable, it also underpins NASA's ambitious astrobiology program. Find another Earth-like planet, astrobiologists say, and life should have happened there too.
NASA is spending billions of dollars to search for life on Mars, the most Earth-like of our sister planets. But we may not need to go all the way to Mars to find another sample of life. It could be lurking under our very noses. No planet is more Earth-like than Earth itself, so if life started here once, it could actually have started many times over.
Geologists believe life established itself on Earth about four billion years ago. Australian rocks dated at 3.5 billion years contain fossilized traces suggesting that microbes were already well ensconced by then. But the ancient Earth was no Garden of Eden. Huge asteroids and comets mercilessly pounded the planet, creating conditions more reminiscent of hell. The biggest impacts would have swathed our globe in incandescent rock vapor, boiling the oceans dry and sterilizing the surface worldwide.
How did life emerge amid this mayhem? Quite probably it was a stop-and-go affair, with life first forming during a lull in the bombardment, only to be annihilated by the next big impact. Then the process was repeated, over and over. As the bombardment began to abate and the impacts diminished in severity, so isolated colonies of primitive microbes sheltering deep underground managed to cling on. One of these colonies was destined to become life as we know it.
What about the preceding life forms? Were they all completely destroyed? It's possible that pockets of microbes could have survived in obscure niches until the next genesis, opening up the tantalizing prospect of two or more different forms of life co-existing on the same planet. Although they would compete for resources, one type of life is not necessarily bound to eliminate the rest. After all, within the microbial realm of "life as we know it," many different species make a living side by side.
Thus, microbes from another genesis - alien bugs, if you will - could conceivably have survived on Earth until today. The chances are that we wouldn't have noticed. Under a microscope, many microbes appear similar even if they are as genetically distinct as humans are from starfish. So you probably couldn't tell just by looking whether a micro-organism is "our" life or alien life. Genetic sequencing is used to position unknown microbes on the tree of life, but this technique employs known biochemistry. It wouldn't work for organisms on a different tree using different biochemical machinery. If such organisms exist, they would be eliminated from the analysis and ignored. Our planet could be seething with alien bugs without anyone suspecting it.
How could we go about identifying "life as we don't know it"? One idea is to look in exotic environments. The range of conditions in which life can thrive has been enormously extended in recent years, with the discovery of microbes dwelling near scalding volcanic vents, in radioactive pools and in pitch darkness far underground. Yet there will be limits beyond which our form of life cannot survive; for example, temperatures above about 270 degrees Fahrenheit. If anything is found living in even harsher environments, we could scrutinize its innards to see whether what makes it tick is so novel that it cannot have evolved from known life.
Identifying alien organisms in more equable settings would be a much harder challenge, especially if they use the same basic molecules as familiar life - nucleic acids and proteins. But there is one sure-fire giveaway. The building blocks of proteins, called amino acids, are all lopsided in the same distinctive way. Viewed in a mirror, these "left-handed" amino acids would appear right-handed. Such mirror-image molecules exist, but the life forms we are familiar with don't use them. Most biochemists think it is just an accident that "life as we know it" selected the left-handed version. If this supposition is correct, then there is a 50-50 chance that alien life would have picked the opposite handedness. Such "anti-life" would eat "anti-food": right-handed amino acids and other mirror molecules. This offers a simple way to filter out known life from anything alien. Prepare a culture medium of anti-food and see if anything flourishes. Of course it's a long shot, but it is easy to try, and scientists at the Marshall Space Flight Center are now testing the response of microbes from various extreme environments to a bowl of anti-soup.
Even if alien life has not endured to the present day, it may still have left its mark. Geochemists have identified organic detritus from ancient microbes in rocks as old as 2.7 billion years. Alien organisms might have left remnants containing peculiar suites of molecules or produced distinctive geochemical alterations like unusual mineral deposits.
These remnants would still give us a genuine second sample, a form of biology that is unrelated to familiar life. By comparing the way evolution works in both cases, we could identify which features of life follow from general principles and which are just accidents of history.
But there is a more profound dimension to this research. Nobody knows how life began. Somehow a mixture of lifeless chemicals assembled itself into a primitive organism, presumably through a long and complex sequence of chemical reactions. Our ignorance of this process is so great that scientists can't even agree on whether it was a gigantic, one-time fluke, or the expected and frequent outcome of intrinsically bio-friendly natural laws, as the astrobiologists hope. Jacques Monod, a Nobel Prize-winning biologist, was adamant that life is a bizarre accident confined to Earth. On the other hand Christian de Duve, another Nobel laureate, declares life to be "a cosmic imperative," bound to occur wherever Earth-like conditions prevail.
The discovery of a second sample of life on Earth would confirm that bio-genesis was not a unique event and bolster the belief that life is written into the laws of the cosmos. It is hard to imagine a more significant scientific discovery. Our view of the universe and our place within it would be forever transformed, and we would at last have the answer to the biggest of the big questions of existence: Are we alone?
Paul Davies, a professor at the Australian Center for Astrobiology at Macquarie University, is the author of "The Fifth Miracle: The Search for the Origin and Meaning of Life."
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