All my life I have wondered about the possibility of life elsewhere. What would it be like? Of what would it be made? All living things on our planet are constructed of organic molecules — complex microscopic architectures in which the carbon atom plays a central role. There was once a time before life, when the Earth was barren and utterly desolate. Our world is now overflowing with life. How did it come about? How, in the absence of life, were carbon-based organic molecules made? How did the first living things arise? How did life evolve to produce beings as elaborate and complex as we, able to explore the mystery of our own origins? And on the countless other planets that may circle other suns, is there life also? Is extraterrestrial life, if it exists, based on the same organic molecules as life on Earth? Do the beings of other worlds look much like life on Earth? Or are they stunningly different — other adaptations to other environments? What else is possible? The nature of life on Earth and the search for life elsewhere are two sides of the same question — the search for who we are. In the great dark between the stars there are clouds of gas and dust and organic matter. Dozens of different kinds of organic molecules have been found there by radio telescopes. The abundance of these molecules suggests that the stuff of life is everywhere. Perhaps the origin and evolution of life is, given enough time, a cosmic inevitability. On some of the billions of planets in the Milky Way Galaxy, life may never arise. On others, it may arise and die out, or never evolve beyond its simplest forms. And on some small fraction of worlds there may develop intelligences and civilizations more advanced than our own. Occasionally someone remarks on what a lucky coincidence it is that the Earth is perfectly suitable for life — moderate temperatures, liquid water, oxygen atmosphere, and so on. But this is, at least in part, a confusion of cause and effect. We earthlings are supremely

An honest man, armed with all the knowledge available to us now, could only state that in some sense, the origin of life appears at the moment to be almost a miracle, so many are the conditions which would have had to have been satisfied to get it going. But this should not be taken to imply that there are good reasons to believe that it could not have started on the earth by a perfectly reasonable sequence of fairly ordinary chemical reactions. The plain fact is that the time available was too long, the many microenvironments on the earth's surface too diverse, the various chemical possibilities too numerous and our own knowledge and imagination too feeble to allow us to be able to unravel exactly how it might or might not have happened such a long time ago, especially as we have no experimental evidence from that era to check our ideas against.

An honest man, armed with all the knowledge available to us now, could only state that in some sense, the origin of life appears at the moment to be almost a miracle, so many are the conditions which would have had to have been satisfied to get it going. But this should not be taken to imply that there are good reasons to believe that it could not have started on the earth by a perfectly reasonable sequence of fairly ordinary chemical reactions. The plain fact is that the time available was too long, the many microenvironments on the earth's surface too diverse, the various chemical possibilities too numerous and our own knowledge and imagination too feeble to allow us to be able to unravel exactly how it might or might not have happened such a long time ago, especially as we have no experimental evidence from that era to check our ideas against. Perhaps in the future we may know enough to make a considered guess, but at the present time we can only say that we cannot decide whether the origin of life on earth was an extremely unlikely event or almost a certainty — or any possibility in between these two extremes.

An example of such emergent phenomena is the origin of life from non-living chemical compounds in the oldest, lifeless oceans of the earth. Here, aided by the radiation energy received from the sun, countless chemical materials were synthesized and accumulated in such a way that they constituted, as it were, a primeval “soup.” In this primeval soup, by infinite variations of lifeless growth and decay of substances during some billions of years, the way of life was ultimately reached, with its metabolism characterized by selective assimilation and dissimulation as end stations of a sluiced and canalized flow of free chemical energy.

[W]e can't agree among ourselves, as an origins of life community, what were the conditions... under which life arose on earth. ...Within the field itself, probably the leading candidate... would be terrestrial geothermal systems, starting with and powered by UV radiation. There's been a lot of rather beautiful chemistry... in a terrestrial environment in some kind of geothermal pool... and cyanide chemistry, it works well as chemistry. The problem I have with that is that it doesn't link up very well to biochemistry of cells. I'm a biochemist and I would like to see some continuity between and , and there's not much there, to me. That doesn't mean that it's wrong. It's just that... [I] would like to see some continuity.

The first living organisms on Earth doubtless arose in an aqueous environment, and the course of evolution has been shaped by the proper­ ties of the aqueous medium in which life began.

Not only did life originate on earth very early in its history as a planet, but for the first two billion years, Earth was inhabited solely by bacteria.

Looking from the astrobiology perspectives, life on Earth started early—just about as soon as it could. The more we learn about the origin of life, the more we realize it may be a likely outcome any time you have the right ingredients. However, if you look at the history of life on Earth, let’s say you put it on a twelve-hour clock, up until four o’clock it was just a world of microorganisms, from four to five o’clock that’s the era of plants coming onto land and animals and creatures in the sea, then after five o’clock until about ten o’clock this will be a world of only microorganisms again. So, in fact, our planet is in its late middle ages in terms of life on the surface. Then from ten o’clock until about midnight, the world will be completely desolate, devoid of life as the sun is running out of its nuclear fuel in the center and its outer atmosphere is expanding. The point is that our world has had big life for only a small slice of its existence and the portion of that which has had technology is even smaller. I think life is presumably abundant everywhere; the most common form is likely going to be microbial life. In addition, the distances are so vast that unless other civilizations have developed both a means of crossing those distances quickly and the desire to do so, plus the energy capability, I don’t know if we’ll see alien intelligence in our lifetime.

The probability that at ordinary temperatures a macroscopic number of molecules is assembled to give rise to the highly ordered structures and to the coordinated functions characterizing living organisms is vanishingly small. The idea of spontaneous genesis of life in its present form is therefore highly improbable, even on the scale of the billions of years during which prebiotic evolution occurred.

The origin of life happened in significantly less than 500 million years. ...Six days was once a popular hypothesis. ...A process that happens quickly is a process that is in some sense likely... this evidence suggests that the origin of life was in some sense easy, in some sense sitting in the laws of physics and chemistry.

If you search the scientific literature on evolution, and if you focus your search on the question of how molecular machines—the basis of life—developed, you find an eerie and complete silence. The complexity of life’s foundation has paralyzed science’s attempt to account for it; molecular machines raise an as-yet-impenetrable barrier to Darwinism’s universal reach.

What I am trying to do is to present a unified scientific view of life; that is, a view integrating life's biological, cognitive, and social dimensions. I have had many discussions with social scientists, cognitive scientists, physicists and biologist who question that task, who said that this would not be possible. They ask, why do I believe that I can do that? My belief is based largely on our knowledge of evolution. When you study evolution, you see that there was, first of all, evolution before the appearance of life, there was a molecular type of evolution where structures of greater and greater complexity evolved out of simple molecules. Biochemist who study that have made tremendous progress in understanding that process of molecular evolution. Then we had the appearance of the first cell which was a bacterium. Bacteria evolved for about 2 billion years and in doing so invented, if you want to use the term, or created most of the life processes that we know today. Biochemical processes like fermentation, oxygen breathing, photosynthesis, also rapid motion, were developed by bacteria in evolution. And what happened then was that bacteria combined with one another to produce larger cells — the so-called eukaryotic cells, which have a nucleus, chromosomes, organelles, and so on. This symbiosis that led to new forms is called symbiogenesis.

Organic life, we are told, has developed gradually from the protozoon to the philosopher, and this development, we are assured, is indubitably an advance. Unfortunately it is the philosopher, not the protozoon, who gives us this assurance.

Life is not found in atoms or molecules or genes as such, but in organization; not in symbiosis but in synthesis.