What are the origins of life on Earth? How did things go from non-living to living, from something that could not reproduce to something that could? How can a collection of inanimate atoms become animate? How did organic molecules achieve a high enough level of complexity to be considered as “living”? The short answer is: we do not really know how life originated on this planet. The longer answer, however, is much more interesting.
The study of the origin of life on Earth or, more specifically, how life on Earth began from inanimate matter, is technically known as abiogenesis (as opposed to biogenesis, which is the process of lifeforms producing other lifeforms, and as opposed to evolution, which is the study of how living things have changed over time since life first arose).
The modern definition of abiogenesis, however, is concerned with the formation of the simplest forms of life from primordial chemicals, rather than the old Aristotelian concept of abiogenesis, which postulated the formation of fully-formed complex organisms by spontaneous generation. It becomes, then, the search for some kind of molecule (along the lines of RNA or DNA) that is simple enough that it can be made by physical processes on the young Earth, yet complicated enough that it can take charge of making more of itself, which is probably what most people would recognize as constituting “life”.
The first living things on Earth, single-celled micro-organisms or microbes lacking a cell nucleus or cell membrane known as prokaryotes, seem to have first appeared on Earth almost four billion years ago, just a few hundred million years after the formation of the Earth itself. By far the longest portion of the history of life on Earth, therefore, has involved the biochemical evolution of these single-celled micro-organisms, bacteria and archaea: we can find individual fossilized microbes in rocks 3.4 billion years old, yet we can only conclusively identify multi-celled fossils in rocks younger than 1 billion years.
It is presumed that, over a few hundred million years of evolution, pre-biotic molecules evolved into self-replicating molecules by natural selction. While some aspects of the subject are well understood, others remain clouded in mystery and are the source of much contention among scientists. Although much progress has been made, there is still no single definitive theory.
Life, for all its complexity, is woven out of just 30 or so different molecules, constructed from some of the most abundant elements in the universe: oxygen, hydrogen, carbon, nitrogen, sulphur and phosphorus. However, no one has yet succeeded in synthesizing a “protocell” using basic components which would have the necessary properties of life (something which has been made much of by religious creationists and anti-evolutionists), although recent work work, such as that of Jack Szostak at Massachusetts General Hospital and the Howard Hughes Medical Institute, may be about to change that.
The beginnings of life is, strictly speaking, a matter of biology not physics, and essentially unrelated to most of the rest of the content of this website. I have included a brief discussion of it here, however, partly because it is another aspect of modern science which many people find confusing and puzzling, partly just because I find it really interesting (for which I made no apologies!), and partly because we are, after all, made of “stardust”.
Today I'd like to start a discussion on the ways certain kinds of questions present formidable challenges to the conventional scientific method of explanation, based on hypotheses and empirical validation. Given that the topic is vast and space short, I will divide the discussion into three parts (at least). Although there may be many questions that pose a challenge to the scientific method (for example, the much-debated questions of morality and altruism), I am interested in a trio that can be grouped as the "three origins questions": cosmos, life, and mind.
Working with any of these can fill many lifetimes of research, without any promise of success. In fact, how we measure success in answering any of these questions is already part of the challenge. They each invoke different areas of research, with different operational principles and scientific methodologies. Even so, there are points in common, and it is to those that I turn today, and in subsequent blog posts. (There have been many books and essays written on these three issues, taken together or separately. At the end I provide a list of further reading.)
The first point in common is that not so long ago these three questions were not considered scientific. On the contrary, the origin of the Universe, of life, and of mind were thought to be the result of divine work, products of supernatural intervention. Which god or gods were responsible depended (and still does to the vast majority of the world population) on your particular faith. Differences aside, in any religion only an entity that transcended space and time could create the cosmos, which exists within space and time; only an immortal entity had the power to create life; and only an omniscient power could endow His creatures with intelligence and a sense of being.
The confrontation with natural processes is immediate: Nature is within space and time, living entities are not immortal and no one is — or can be — omniscient. (Although the World Wide Web, allied with global human intelligence and powerful search engines, could, in some sense, be called a proto-omniscient entity. Stuff for another week.)
For this reason, it is not at all surprising that scientists encounter such resistance when they state that they are near — or at least making progress — in answering such questions without recourse to divine intervention. According to the scientific viewpoint, the origins of the cosmos, of life and of mind are natural processes that obey material laws and principles. Their complexity and our current lack of answers do not mean that such questions are completely beyond the reach of science, or that such questions can only be addressed through religious belief. In science, ignorance is the pre-condition to knowledge; to not-know is the pathway to knowing.
Perhaps the proper way to phrase the question is not whether science can provide answers to the three origins but how far it can go in answering them. For it may very well be that science can only go part of the way. To see why, let's begin with the one that may, perhaps, be the "easiest" of the three, the origin of life.
Although we are far from understanding the details (see guest blogger Wim Hordijk's recent contribution to these pages), it seems clear that the transition from non-life to life follows from the increasingly complex chemical reactions that took place on primal Earth: at a certain point, networks of chemical reactions became self-sufficient and, partially isolated within protective membranes, were able to absorb energy from the outside environment and to produce copies of themselves with some efficiency. We certainly don't know how this happened here some 3.5 billion years ago (or even earlier).
More to the point, unless someone offers a formal proof that there is only one biochemical pathway toward life — a possibility that I consider highly unlikely — we will never be able to know exactly how life emerged here. At best, we can come up with viable scenarios of the origin of life given the conditions prevalent on primal Earth (another challenge in itself, to find those out).
So, the question of the origin of life, at least in the exact way (or ways, for it may have happened more than once) in which it emerged here or in any other planetary platform out there, is not answerable scientifically. Does this mean that science can't help us understand the origin of life? Not at all. We can only understand the origin of life through science, even if this understanding is necessarily limited. Of the three origins questions, the origin of life is still the most tractable, given that we can simulate conditions and chemical reactions in the laboratory with some degree of control.
Contrary to the origin of the Universe or of mind, the origin of life is a problem we can attack from the outside in. It is for this reason that I call it the "easiest" of the three, although there is nothing easy about it.
Molecular biologists like Gerald Joyce, from the Scripps Research Institute in La Jolla, and Nobel laureate Jack Szostak from Harvard University, among many others, are making spectacular advances toward understanding life. They can manipulate RNA and DNA and coax them into enacting the game of life, that is, respond and adapt to environmental pressure as the theory of evolution dictates; they can strip away cellular structures and genes from living cells to search for the minimum living system; Günter von Kiedrowski in Germany was able to construct auto-catalytic chemical sets that show self-replicating abilities.
These experiments are not yet creating life in the laboratory. But they are certainly steps in the right direction. Even if we will not be able to explain exactly how life emerged on Earth, science still offers the only pathway toward understanding.
A writer wannabe. I am interested in writing short stories. I regard myself primarily as a poet. I love the arts. I am passionate about preserving the territorial integrity of Vietnam against the current Chinese quiet take-over.
