The discovery of extraterrestrial life of any size would likely be one of the most significant events in the history of humanity. Such a finding, particularly if within our own Solar System, would suggest that life is common throughout the universe and that the terrestrial biosphere is not a hopelessly rare phenomenon.

The chances that a planet, or perhaps a moon, in a nearby star system harbors intelligent life forms and that technological civilizations span our galaxy would increase dramatically, simply because of the large number of living worlds available.

After all, even if only one out of every thousand living worlds were able to produce intelligent life, if there were billions of living worlds then we would still be left with millions of places where intelligent beings have evolved.

So, the discovery of Martian life for instance, even if we are talking about Martians so small that they could be seen only with a microscope, would have serious implications when viewed in the context of our search for extraterrestrial intelligence (SETI).

But in addition to giving SETI a very good reason for optimism, the study of extraterrestrial microbiology would and should move beyond merely finding that ET microbes exist and, if it does, it can impact the lives and health of all people.

The study of life from another planet is sure to advance our understanding of biology and affect biotechnology and medicine in ways that we can hardly begin to imagine.

Despite the diversity of terrestrial life, all life on Earth is basically the same. All life forms on Earth share a common core of biochemical reactions that are ancient and whose hereditary molecular coding has changed little while similar coding, unrelated to these reactions, has changed a lot in the course of evolution.

In all terrestrial life forms, this hereditary coding is preserved in the form of long molecules, called DNA and RNA. While each organism carries a different message in its DNA, all messages are written and read according to a common language that we call the genetic code.

Indeed, it is because of the commonality of DNA and the genetic code used to read it that it is possible to clone a gene from one species and make it work inside an organism of a different species.

The genetic code is the same for all life on Earth because the molecular machines that read and decode DNA inside all terrestrial organisms are all programmed to use the same language.

Of course, these molecular decoding machines are themselves part of the most ancient biochemical workings of all cells on Earth. Therefore, the DNA of every terrestrial life form contains instructions for making the decoding machinery that is used to read the instructions!

Life that is native to another planet will not necessarily speak our genetic language. It may, for example, have evolved to work according to a different genetic code.

If this were the case, then a gene for a particular protein from an alien life form, when inserted into a terrestrial bacterium, would not produce the same protein that it produces in the alien.

Moreover, the alien life might operate not only according to a different language but an entirely different alphabet. In other words, it may use something other than DNA to encode its genetic instructions.

Considering the fact that we've understood how our own genetic alphabet (DNA) and language (the Genetic Code) work for only a half century and what this understanding has already done for biology and medicine, the implications of discovering other living systems are staggering.

When viewed from this perspective, all life on Earth amounts to but a single datum. We are currently mining this one datum for all we can get from it, which is a lot.

But our knowledge of biology is still as limited as our knowledge of chemistry would be were it based on experience with only one element, such as neon or argon. We would be experts on neon but there would be no atomic theory and no periodic table.

That means we would not understand chemistry as a universal science, based on fundamental laws that are as predictable on the other side of our galaxy as they are here on Earth.

Similarly, by studying our single datum in biology, we can become experts on how one type of life does things. And we should do this since it is our own type of life. Indeed, before we know it, this course of action may lead to the creation of an artificial bacterium from scratch in the laboratory.

People are working on this now and it would be the no less than the creation of life from non-living ingredients. But, although such a project would result in a new species, it would still be our own kind of life and it would be created by imitating nature, without necessarily understanding the role of all of the ingredients.

In contrast, our second datum in biology, which could come from Mars, might teach us an entirely different way of running a cell. This knowledge could be very powerful, as we would be able to compare two of nature's approaches to life, each having emerged from non-living chemistry independent of the other.

Then we may finally begin to understand life, not as a special case in which this gene is required to do this or another gene is required to do that, but as a fundamental property of the universe.