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Old 01-29-2017, 06:01 PM
Leah S Leah S is offline
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Join Date: May 2008
Posts: 17
Default Life on Other Planets – A Biologist’s Viewpoint

At the PAS meeting on January 19, Dr Lauren Edgar shared some very interesting information about the discoveries of the rover “Curiosity”, including the possibility that there might have once been a measurable amount of water on Mars. A PAS member asked whether they had found any signs of life, and added, “maybe primitive life, like amebas…”

I would like to comment on this as a biologist (M.Sc., Zoology).

While it is known that water is essential for life, the presence of water does not necessarily guarantee the development of living organisms. The equation doesn’t work both ways. Just as – you need to buy a ticket in order to win the lottery, but having a ticket won’t guarantee that you will win the jackpot.

Even “primitive” organisms, such as protozoans and bacteria, are incredibly complex. They must carry out all functions of a full organism, with only one cell to do it! For example, they must be able to ingest food, digest it, and metabolize it to release energy, in a way that the energy can be utilized afterwards to power other activities. They must be able to eliminate waste products, and to manufacture proteins – both structural proteins and enzymes (which are proteins that carry out various reactions). They must be able to detect stimuli and respond to them, e.g. moving towards food or away from danger. And they must be able to duplicate their DNA and undergo mitosis (cell division), which is quite a complex choreography.

In “higher” organisms, specialized cells (arranged in tissues and organs) carry out various functions. But a one-celled organism must do it all!

Scientists have not yet found an explanation for how life was spontaneously generated on our own planet, much less on others. The logistics are against it, even in a nurturing environment such as Earth, which has had a moderate temperature and large amounts of liquid water for billions of years. Just to give one example: a protein is a chain of hundreds of amino acids, but not every series of amino acids is a functional protein, just as not every series of letters is a real word. The specific order of various amino acids in the protein chain determines its 3-dimensional structure, which in turn will determine whether it is a functional protein, and what it will be able to do. And a living cell, even the smallest bacterium, requires many different kinds of functional proteins, and many identical molecules of each one. Even if we imagine a pond or lagoon that is full of amino acids ready to randomly organize themselves into protein chains, it would be highly unlikely for even one functional protein molecule to spontaneously appear, much less several different kinds, with several identical copies of each – just as we do not usually find one of Shakespeare’s sonnets (or even one logical sentence) spontaneously appearing in a bowl of alphabet soup. The “pond full of amino acids” is theorized for the purpose of justifying the spontaneous generation of the first life, but there is no sign that any such pond ever existed. Also, besides the mystery of how the first proteins arose, the origin of the genetic code in DNA is another mystery.

So the jump from inanimate matter to life is quite large, even under ideal conditions. If it were easy for life to be generated, we would expect to see life arising on Earth several times in its history; instead we see it appearing only once, and all living things today are descended from that one event.

Some people point to extremophiles (organisms that can survive in hostile environments, such as high temperature, pressure, or acidity) as evidence that life can be spontaneously generated even in extreme environments. However, it is important to realize that the ancestors of today’s extremophiles originally lived and developed in a much more nurturing environment. After living cells already existed, some of them were able to adapt to extreme conditions as well. But they did not originate there.

I believe that NASA and other organizations encourage people to believe that life can easily be spontaneously generated on any planet that has water, or even other solvents (such as moons with an “ocean” of liquid alcohol or methane); and for a very prosaic reason. Suppose NASA wants to ask for funding for a space probe to explore the geography of a planet or moon. As an astronomer, I would find that fascinating, but the response of the general public is: “Didn’t we already launch a space probe once? Why should we spend money on another space probe when we can spend it on another baseball stadium!!!!” But if NASA says, “we want to send a space probe because we think we might find *water*! And you know that if there’s water, there’s got to be life – at least primitive life!” – people open their wallets and ask, “how much do you want?”

I think that even if this is what they are “selling” to the public, as astronomers we should at least be aware of the true probabilities regarding the spontaneous generation of life on other planets.
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