"Where did this first primal cell come from? Did Darwin have any answer to that?"
"I said, did I not, that he was a very cautious man. But as regards that question, he did permit himself to propose what one might call a qualified guess. He wrote:
If (and O, what an if!) we could picture some hot little pool in which all manner of ammoniacal and phosphorous salts, light, heat, electricity and so forth were present, and that a protein compound were to be chemically formed in it, ready to undergo even more complicated changes ..."
"What then?"
"What Darwin was philosophizing on here was how the first living cell might have been formed out of inorganic matter. And again, he hit the nail right on the head. Scientists of today think the first primitive form of life arose in precisely the kind of 'hot little pool' that Darwin pictured."
"Go on."
"That will have to suffice because we're leaving Darwin now. We're going to jump ahead to the most recent findings about the origins of life on earth."
"I'm rather apprehensive. Does anybody really know how life began?"
"Maybe not, but more and more pieces of the puzzle have fallen into place to form a picture of how it may have begun."
"Well?"
"Let us first establish that all life on earth--both animal and vegetable--is constructed of exactly the same substances. The simplest definition of life is that it is a substance which in a nutrient solution has the ability to subdivide itself into two identical parts. This process is governed by a substance we call DNA. By DNA we mean the chromosomes, or hereditary structures, that are found in all living cells. We also use the term DNA molecule, because DNA is in fact a complex molecule--or macro-molecule. The question is, then, how the first molecule arose."
"Yes?"
"The earth was formed when the solar system came into being 4.6 billion years ago. It began as a glowing mass which gradually cooled. This is where modern science believes life began between three and four billion years ago."
"It sounds totally improbable."
"Don't say that before you have heard the rest. First of all, our planet was quite different from the way it looks today. Since there was no life, there was no oxygen in the atmosphere. Free oxygen was first formed by the photosynthesis of plants. And the fact that there was no oxygen is important. It is unlikely that life cells--which, again, can form DNA--could have arisen in an atmosphere containing oxygen."
"Why?"
"Because oxygen is strongly reactive. Long before complex molecules like DNA could be formed, the DNA molecular cells would be oxydized."
"Really."
"That is how we know for certain that no new life arises today, not even so much as a bacterium or a virus. All life on earth must be exactly the same age. An elephant has just as long a family tree as the smallest bacterium. You could almost say that an elephant--or a human being-- is in reality a single coherent colony of monocellular creatures. Because each cell in our body carries the same hereditary material. The whole recipe of who we are lies hidden in each tiny cell."
"That's an odd thought."
"One of life's great mysteries is that the cells of a multicellular animal have the ability to specialize their function in spite of the fact that not all the different hereditary characteristics are active in all the cells. Some of these characteristics--or genes--are 'activated' and others are 'deactivated.' A liver cell does not produce the same proteins as a nerve cell or a skin cell. But all three types of cell have the same DMA molecule, which contains the whole recipe for the organism in question.
"Since there was no oxygen in the atmosphere, there was no protective ozone layer around the earth. That means there was nothing to stop the radiation from the cosmos. This is also significant because this radiation was probably instrumental in forming the first complex molecule. Cosmic radiation of this nature was the actual energy which caused the various chemical substances on the earth to start combining into a complicated macro-molecule."
"Okay."
"Let me recapitulate: Before such complex molecules, of which all life consists, can be formed, at least two conditions must be present: there must be no oxygen in the atmosphere, and there must be access for cosmic radiation."
"I get it."
"In this 'hot little pool'--or primal soup, as it is often called by modern scientists--there was once formed a gigantically complicated macromolecule, which had the wondrous property of being able to subdivide itself into two identical parts. And so the long evolutionary process began, Sophie. If we simplify it a bit, we can say that we are now talking of the first hereditary material, the first DNA or the first living cell. It subdivided itself again and again--but from the very first stage, transmutation was occurring. After aeons of time, one of these monocellular organisms connected with a more complicated multicel-lular organism. Thus the photosynthesis of plants also began, and in that way the atmosphere came to contain oxygen. This had two results: first, the atmosphere permitted the evolution of animals that could breathe with the aid of lungs. Secondly, the atmosphere protected life from the harmful cosmic radiation. Strangely enough, this radiation, which was probably a vital 'spark' in the formation of the first cell, is also harmful to all forms of life."
"But the atmosphere can't have been formed overnight. How did the earliest forms of life manage?"