The origin of the biosphere

The biosphere is the ensemble of the life-supporting regions of the terrestrial globe. It is made up of the oceans and fresh waters, plus the atmosphere and the layer of soil (spread over the continents) that contains organic matter. Water is the predominant component of the biosphere, in which the atmosphere plays an important role, and where the many compounds of carbon are essential because they are needed by life. In the outer crust of the Earth, however, inorganic carbon is by far the most abundant component, in the form of carbonates (limestone, dolomite, etc.). Heat easily decomposes carbonates and frees carbon in the form of carbon dioxide (CO2); thus this process is the principal source of volcanic CO2.

For a long time, the origin of the biosphere remained a mystery, because no fossil trace exists from the first billion years of the Earth's evolution.

The nervous system

Living organisms learned very early on that the detection of changes happening in their environment was essential if they were to survive. Some photosynthetic algae had already learned how to move by wagging their flagellum, in order to look for places where lighting was optimal. The first multicellular organisms increased their chances of survival by detecting changes in their own body, and thus coordinate the response from their different cells.

Contact between one cell and its neighbors developed in the plants by means of enzyme exchange; that is, in a purely chemical way. It is a very slow process which leads to tropisms (such as the flower that turns toward the Sun, or the foliage that seeks light). But tropisms are too slow for animals; quick reactions for attack or defense are essential. A faster communication system appeared: some cells specialized in sending swift electrical impulses from one cell to another, as if along an electric wire. The nervous system began to emerge.

The life of the stars

At the time when the first quasars showed their dazzling brilliance, there were still no atoms of carbon, nitrogen, or oxygen, no metals in the Universe, nor any solid stuff (earth, rocks, etc.). It is tempting to think that the extreme temperatures reached in the accretion disks of quasars would have already produced new elements. But we must remember that the rings that reached a sufficiently high temperature were eventually absorbed by the black hole and disappeared from our Universe before having had a chance to make complex molecules.

The first stars formed out of a gaseous mixture of about 76% hydrogen and 24% helium, plus a few traces of rare light elements, such as lithium, or rare isotopes like deuterium or 3He. Table 3.1. Major thermonuclear reactions within stars, classified by increasing ignition temperature, from 10 million degrees for hydrogen, up to 6 billion degrees for iron

The minimum stellar mass able to reach this ignition temperature is indicated in solar mass units M⊙.

The grand beginning

Let us summarize the initial events in their chronological order. First, we can imagine a quantum fluctuation in the void, which began everything. The perfect symmetry of the little bubble of pure energy is unstable and breaks up spontaneously. We follow it at the instant when it is still smaller than a proton. It inflates exponentially while creating its space–time dimensions and, after 10-32 second, it is already larger than the present Solar System. This exponential ‘inflation’ (see Appendix F) creates all the matter and all the radiation still present in the Universe.

After that, the phase transition ends. The change of state has forever broken the initial symmetry. From now on, only the nuclear forces will remain confined between the quarks, whereas the forces of gravity and electromagnetism now act at a distance. The Universe will continue its expansion in an almost linear manner, restrained merely by gravitation, right up to the present.

But where did all this energy come from, with its ability to create the enormous bulk of matter and radiation that we see in the stars and the galaxies?

From the Big Bang to the human brain, it has taken the universe some fifteen billion years of cosmic, physical, chemical, and biological evolution to reach a stage where, on our own little speck of dust, it is beginning to look into itself and ponder its origin, nature, and significance.

How did it all happen? What is known, suspected, or assumed of each of the steps whereby time and matter first arose out of nothing, elementary particles condensed out of the original plasma, and, out of them, in turn, the atoms of the various elements came to be? Of the steps whereby galaxies were born, spawning billions of stars, many probably surrounded by planetary systems? Of the steps whereby, on one particular planet, which happened to combine a special set of physical conditions, life emerged and evolved, finally leading to conscious, thinking beings?

How much of this extraordinary history is due to deterministic forces, how much to chance? Did it happen only once? Or does the cosmos contain many planets that have given rise to life, perhaps even to intelligent life? What is it about the cosmological constants that endows our universe with its unique properties? Is only one such universe possible? Or are there many universes, of which ours happens to bear life and mind, and thus to be knowable, because of a special combination of cosmological constants? What triggered the Big Bang? A creative act of God? Or just randomly fluctuating nothingness?

The evolutionary thread

This book has tried, chronologically, to tell a history of the Universe that began with the Big Bang and continues up to our existence. In spite of many uncertain details and incomplete interpretations, the remaining gaps have not obscured a clear thread of ascent toward a greater and greater complexity, going from atoms to molecules to life, from bacteria to animals to humans, from early cultures to societies to civilizations.

It now remains for us to ponder on the vistas that we have opened up, in order to try to see what they reveal, and to understand the nature of what could still be concealed. Still following the thread of chronology, as long as it remains useful, let us first consider what could have happened before the Big Bang.

The ‘Augustinian era’

In 1952, George Gamow wittily proposed calling the period that might have occurred before the Big Bang the ‘Augustinian era’, because Saint Augustine was the first to raise the question of knowing what God did before He created Heaven and Earth.

Matter is made up of two kinds of elementary particle, quarks and leptons, each having six varieties divided into two groups of three:

Quarks

Leptons

Usual matter

Mesons

Forces of nature

Four types of force of different symmetries occur among matter particles; these forces are carried by particles of a new kind:

1. (1) electromagnetism, carried by the photon (light, X-rays, γ rays, etc.)

2. (2) the weak force is carried by three particles: W+, W- and Z0

3. (3) the strong force is carried by eight ‘colors’ of gluons

4. (4) gravitation is carried by the graviton

The standard model unifies electromagnetism and the weak force, as if the three particles W+, W- and Z0 were actually heavy photons.

The existence of the top quark had been predicted for a score of years; it was finally observed in 1994, completing the list of elementary particles.

Humankind has just awoken to the cosmic origins of the human adventure and I have striven to reconstruct this story as science now sees it. In order to keep it accessible to the enquiring reader, I have not used mathematics but followed the thread of chronology.

Recently, it has become possible to tell this story without leaving too many gaps. At the beginning of this century, the different natural sciences, originating in the same discipline of natural philosophy, had become specialized; they were cut off from one another. Now, physics, cosmology, astronomy, chemistry, geology, paleontology, biochemistry and biology are coming together again.

So my thread follows the Universe from the moment of its beginning; I tell how its expansion led to the formation of the galaxies and stars. The pursuit of the thread shows us how life could finally emerge, through the most probable cosmic processes, while using the most abundant elements made in the crucible of the stars' cores.

I have tried to keep the story simple; I cannot say that I have always succeeded. Occasionally, I had to cut short explanations that might have become tedious. The pages that seem too difficult can be skipped; in order to help the reader to follow the thread to the final goal, I have tried to give short summaries throughout the book.

The purpose of the first chapter is to familiarize the reader with the extremely large and the extremely small.

The standard model does not try to explain the cause of the Big Bang. It starts from the present conditions of average density and temperature in the Universe. If we go backwards in time, the Universe was smaller; its density and temperature can be computed for some typical epochs in the past.

1. (1) Average density. The present Universe is very unhomogeneous, so that its average density can be estimated only by using a very large volume, for instance, a cube of 500 million light-years on each side, for which the total mass of millions of galaxies can be assessed. The average density found by this method is a little less than 10-30 g/cm3.

2. (2) Average temperature. There are now still 3 billion photons at 2.7 K in the fossil radiation coming directly from the Big Bang, for each hotter photon arriving from the stars. These stellar photons are therefore the insignificant and negligible traces left by the fireworks from the primordial explosion. The average temperature of the Universe is 2.7 K.

3. (3) Expansion velocity. Its rate is given by the Hubble constant, H, which can be taken, for instance, as H = 25 km/second per million light-years.

In Table E.1, results have been rounded to the nearest factor of 10. The Universe cooled, as for example in an explosion gases cool as they fill a larger and larger volume, so that it is easy to compute the temperature and density at different times in the past.

Excerpts of the letter referred to in this note appear in Appendix C.

Dear Colleagues,

Though the attached letter to prospective participants of your Colloquium provides most of the essential information, let me emphasize that the success of the Colloquium will depend on the skills of the moderators.

The attached letter will be mailed to all prospective panelists together with the invitation. We hope that its message is clear, and that it will make your chore easier.

As soon as the final composition of your panel of discussants is clear, we will ask you to contact them and to obtain a rough outline of the issues they wish to present. Thereafter, it will be up to you to coordinate the sequence of presentations, and to familiarize all panelists with the issues to be considered.

Hopefully, you will be able to prevent talks that exceed 10 minutes. If the discussants adhere to the time schedule, there will be 40–50 minutes for a general discussion with questions from the audience.

Most scientific meetings involve more than one type of event. One can look at these events as building blocks, and it is their combination and placement that will be instrumental for the success of the meeting (see Chapter 5). The following listing is arbitrary and merely highlights options that can be modified to suit a particular situation.

Scientific events

Lectures

All good lectures have one thing in common: they are not too long. It seems that all over the world the attention span has shrunk during recent decades. Blame it on our hectic lifestyle or the impact of the mass media: most people get restless when lectures exceed one hour.

To prevent monotony, lectures (with the possible exception of Main Lectures) should be followed by a discussion period and a break. The length of the break must vary with the circumstances, as detailed in the following sections. However, even ‘Short Communications’ should be scheduled at least three minutes apart. During sessions with several consecutive lectures, one or two extended breaks are definitely indicated (see below).

Within a series of lectures, it is imperative to leave the time slot unused if a speaker does not show up, unless the change can be announced well in advance. Otherwise, participants may miss the event. Any change of schedule during a meeting is likely to cause confusion.

Punctuality of lectures is a must when parallel sessions are held. A cautionary example: At an international conference convened in a country known for its ‘relaxed’ lifestyle, the projectionists appeared routinely late after lunch and resumed their jobs at different times.