The Privilege of Life on Earth

For years scientists such as the late Carl Sagan have — even complex, intelligent life — are so easily met that there must be millions and millions of Earth-like planets existing in the universe. According to this view, the Earth is a "mediocre" planet, just one of a countless multitude peppering the cosmos. Adherents of this view have called the principle that Earth-like planets were easily formed the "Copernican Principle," or the "Principle of Mediocrity." Implicit in their adherence to the "Copernican Principle" was an anti-Christian bias, built upon their desire to demote the special status of Earth as revealed in Sacred Scripture.

But recent advances in science are demonstrating that life demands very particular conditions which are quite difficult to meet. In fact, these conditions must be met not only on a planet, but in the solar system and galaxy which support it. Dr. Guillermo Gonzalez, a fellow of the Discovery Institute — the Seattle-based think tank on Intelligent Design — is one of the leading researchers in this area. With Discovery Institute fellow Jay Richards, he is currently working on a book which argues not only that Earth was designed for complex, intelligent life, but that the position of the Earth makes it the best observation point from which intelligent inhabitants might view the universe. "What better mandate could we have for the scientific enterprise than to discover that the universe is set up for it?" he asks.

Dr. Gonzalez is an Assistant Research Professor of Astronomy at the University of Washington in Seattle, Washington, where he received his PhD in Astronomy in 1993. He has received a number of fellowships, grants, and awards from such institutions as the University of Washington, Sigma Xi (a scientific research society), and the National Science Foundation, and has published over forty articles in refereed astronomy and astrophysical journals.

You are involved in a kind of "Copernican Revolution" in astrophysics — or better yet, a revolution that seems to undermine the "Copernican Principle." Just what is the Copernican Principle, and how does your work throw it into question?

Gonzalez:   The Copernican Principle derives its name from Nicolaus Copernicus, the famous Polish astronomer of the 16th century. So let's look at the so-called Copernican Revolution first. Copernicus postulated the modern heliocentric model of the solar system — that is, with the sun at the center rather than the Earth.

But the Copernican Principle, sometimes called the "Principle of Mediocrity," takes the comparatively trivial physical statement — that the Earth is not the physical center of the universe or any sub-cluster of matter — and moves into the realm of philosophy and theology. Not only do we not occupy the physical center of the universe, we have no special qualities whatsoever. We are only a mediocre planet!

But we are not a mediocre planet?

Gonzalez:   No, not at all. The claims by many Copernican Principle advocates over the centuries, that life is commonplace on other celestial bodies, has been a spectacular failure. Just about every other body in the solar system (including the sun) has been claimed, at one time or another, to harbor intelligent life. Today, we know this not to be the case. There is also widespread doubt that even the simplest kinds of life, such as bacteria, could exist anywhere else in the solar system.

So what we have, with the Copernican Principle, is the expansion of legitimate physical data to unjustified metaphysical conclusions. Just because the Earth is not the physical center of the universe does not mean that it is an ordinary planet — merely one of the millions or billions of planets capable of supporting life?

Gonzalez:   That's right. Since it is Earth's ability to support life that many take to be its most important quality, it is clear that this is a major failure of the metaphysical version of the Copernican Principle if the actual conditions which support life are so rare that they may only exist for Earth.

We might say, then, that while the Earth is not the physical center of the universe, it seems, paradoxically, that it is the "center" in a more significant sense.

Gonzalez:   Yes. If you consider the Earth in the "parameter space" of habitability, then we are very near the "center." Unfortunately, no one else has made this obvious observation. On the contrary, today scientists with anti-religious agendas continue to employ the historically revisionist and empirically discredited metaphysical Copernican Principle as a club to beat down anyone who publicly expresses religious ideas.

These scientists see the extraordinary nature of the Earth as a threat?

Gonzalez:   Yes. And they have made public statements denouncing such views as "Pre-Copernican."

How does your work fit into all of this?

Gonzalez:   My work, in part, deals with astrobiology from an astronomer's viewpoint. I simply follow the empirical evidence wherever it will lead me, and I try not to let philosophical preconceptions color my interpretations. Over the past decade, I have amassed a body of data that continues to reveal the Earth's uncommon qualities.

What discoveries made you first suspect that Earth is no ordinary planet?

Gonzalez:   My interest in the general topic of astrobiology began about 10 years ago, when I began reading about studies of the long-term maintenance of Earth's climate. I quickly learned that there are multiple factors that affect the Earth's climate on many time scales, all of which had to exist for life to exist. Oddly enough, the available studies by other scientists only included a few of them. I was beginning to realize that the stability of Earth's climate is not a simple "given."

In other words, the climate of Earth, a climate capable of supporting life, is the result of many complex, interrelated factors. Could you give us a few examples?

Gonzalez:   Since the 1960s the data from planetary probes have been showing us the tremendous diversity among the planets in the solar system. Among Earth's unique processes in comparison with the terrestrial bodies are planetary-scale plate tectonics, a hydrological cycle coexisting with land, and a strong magnetic field.

First, as has been known for 20 years, planetary plate tectonics recycles carbon such that its concentration in the atmosphere does not reach very high or very low levels over long time scales. If carbon dioxide levels are too high the Earth becomes too hot, but if they are too low it becomes too cold. In addition, complex oxygen-breathing creatures cannot tolerate too much carbon dioxide.

Now an active planetary interior, which causes the movement of the "plates" of the Earth's crust, is driven largely by heat generated by radioactive decay of long-lived radioisotopes. But the presence of such radioisotopes in a planet cannot just be assumed. How many radioisotopes a planet starts with will depend on its formation details and when it forms in the history of the universe. Planets forming in the future will be endowed with fewer radioisotopes.

This active planetary interior also builds up the continents, which are absolutely essential for life. Without continents we would have a "water world" which would not be able to get mineral nutrients to its sunlight-drenched surface.

On top of all this, the radioisotopes also maintain a partly liquid metallic core, which generates the planetary magnetic field. Without this magnetic field the Earth's atmosphere would not be protected from harmful cosmic ray particles.

We could also look at the size of the Earth as a parameter that must be fine-tuned. Too small a planet and it loses its internal heat too quickly to keep its interior active. Too big a planet and it will have too much water and too thick an atmosphere. Even seemingly minor influences on life, such as the Moon, are being found to have a strong connection. The Moon stabilizes the tilt of the Earth's rotation axis. Without this stabilization, global temperatures would vary over a much greater range.

So the road to life on Earth was not easy and wide, but according to the most recent scientific data, difficult and narrow?

Gonzalez:   Exactly. The trends in astrobiology research continue to narrow the parameter space that a planet must fit into if it is to support life.

What about our solar system? Is it extraordinary as well?

Gonzalez:   Before answering this question, I think it is helpful to split the question into two parts: the sun and the planets. It is relatively easy to compare the sun's properties to those of other stars. In 1999 I compiled a list of properties of the sun and compared them to other nearby stars for which we have reliable data. It turns out that the sun is quite anomalous in several respects, including its mass, light variability, galactic orbit, and composition. Much of this has been known for a couple of decades, but astronomers still make statements like, "the sun is just an average star" in their introductory textbooks.

Just how extraordinary is our sun?

Gonzalez:   For example, the sun is among the 9 percent most massive stars in the galaxy. Its galactic orbit is more nearly circular than about 80 percent of nearby stars its age. It also has more heavy elements than about three-quarters of stars its age.

How does the extraordinary nature of our sun affect life on Earth? Can you give us some examples?

Gonzalez:   If the sun were more variable in its light output, we would suffer greater temperature variations on the Earth. There is mounting empirical evidence that the Earth's climate is quite sensitive to variations in the sun's luminosity. For example, the Little Ice Age during the 17th and 18th centuries is now believed to have been the sun's doing.

Had the sun not had such a large endowment of heavy elements, a terrestrial planet as big as the Earth could not have formed. Or if we had been orbiting one of the much more common low-mass red-dwarf stars, rather than the sun, we would have been blasted by the radiation from their flares.

Let's move on to the second part, concerning the planets.

Gonzalez:   I won't be able to answer the second part until we have the ability to detect Earth-mass planets around other stars. At present, astronomers are detecting Jupiter-mass planets around nearby stars. These discoveries are quite surprising, especially to advocates of the Copernican Principle who were expecting all other planetary systems to look like ours. It turns out that Jupiter-mass planets in large circular orbits are the exception, not the rule.

What is so important about a circular orbit?

Gonzalez:   If we were looking at our solar system from a distance, Jupiter is the only planet we would be able to detect. Jupiter is the most massive planet in our solar system, and it has a nearly circular orbit. This is a good thing, because a less circular orbit would make the solar system less stable.

Just to clarify, are planets with the mass of Jupiter rare, or is it just the circularity of Jupiter's orbit that is rare? And is a Jupiter-mass planet more or less likely to sustain life than a planet the size of Earth?

Gonzalez:   Only about 4 percent of nearby stars are found to have Jupiter-mass planets. While life cannot exist on a Jupiter-like planet, Jupiter does play important roles in the Earth's habitability. It delivered water and carbon-containing molecules to the Earth early on by deflecting asteroids towards it. It has also been deflecting comets from the inner solar system, lest the Earth suffer too many collisions at later times. So even though a Jupiter-like planet cannot sustain life, complex life could not exist on Earth without Jupiter.

These are some amazing instances of fine tuning! Well, let's put the two parts of the original question back together again. Is there any interesting relationship between stars and planets in regard to the possible existence of life?

Gonzalez:   Yes. One area of research I am involved with is the relationship between the compositions of stars and the presence of planets. I discovered in 1996 that planet-hosting stars have a very different composition than stars without planets. I took a bit of a risk in making the link when I did, given the small number of extra-solar planets known at the time. I was, in part, motivated by my rejection of the metaphysical Copernican Principle and my knowledge of the sun's atypical composition. Today, a star's composition is seen as the single most important determining factor of whether massive planets are present. The sun's composition turns out to be anomalous both with respect to stars with planets and stars without planets.

Are you saying that you need a particular kind of star before you can have an Earth-like planet?

Gonzalez:   You need a star with just the right concentration of heavy elements — too much, and giant planets will form in the wrong places or with non-circular orbits; too little, and neither Earth nor Jupiter will form. Incidentally, the planetary system most like ours is that around the star 47 Ursa Majoris. It is interesting that this star is the closest match to the sun among the roughly 60 stars with known planets.

And what about our galaxy? Is it extraordinary as well?

Gonzalez:   Our galaxy too is atypical. But again, most people are unaware of this, except for a few specialists in extra-galactic astronomy. For example, our galaxy is among the 1 percent most luminous galaxies in the nearby universe.

What effect does luminosity have on the Earth? Why is it important?

Gonzalez:   The concentration of heavy elements correlates with the luminosity of a galaxy. More luminous galaxies have more heavy elements, and, thus, are more likely to have Earth-mass planets.

How are others in your field reacting to your arguments? I am assuming that you are challenging scientific orthodoxy, at least in astronomy?

Gonzalez:   They don't know what to make of these evidences. They don't deny the data, but they don't quite know how to fit it into their worldviews. A number of my colleagues have congratulated me for my work. Some astronomers who were originally skeptical have moved in my direction as the evidences have continued to accumulate.

From your writings, I see that you are not a fan of the search for extraterrestrial life, especially intelligent life. Why?

Gonzalez:   I have changed my views on the question of extraterrestrial intelligence (ETI). I grew up reading science fiction and watching science fiction movies like most others of my generation. So it was only natural that I would come to believe in ETI. I started to become skeptical of ETI in the early 1990s as I was beginning to study the requirements for habitability. This, combined with Fermi's Paradox, convinced me that we are alone, at least in the Milky Way galaxy. I first wrote publicly about the reasons for my skepticism of ETI in a Wall Street Journal op-ed on July 16, 1997. It was an unsolicited piece, which I was strongly motivated to write by what I saw as a strong bias in favor of ETI both in the popular press and the scientific community in this country. Later, I was invited to write more extensively on my views in Society, a sociology journal. My article was published in the July/ August 1998 issue.

Having been on the other side of this issue for many years, I know what kinds of arguments people put forth to defend their views of ETI. They are extremely weak arguments, and the motivation comes mostly from wishful thinking. Many researchers involved in the search for ETI, called "SETI," simply don't want to accept evidence that will reduce the probability of their success. In addition, there is a very deep and open hostility to religious views (especially Christian ones) among many SETI researchers. I don't like to name names, but the rantings of the late Carl Sagan are in evidence in the many books he wrote on the subject. He was particularly fond of revising history to fit his anti-religious ideological agenda.

Let's return to some previous questions. You've worked with astronomer Donald Brownlee and geologist Peter Ward, who put forth the "Rare Earth hypothesis" in their book Rare Earth: Why Complex Life is Uncommon in the Universe. What is the Rare Earth hypothesis?

Gonzalez:   The Rare Earth hypothesis simply proposes that Earth-like planets capable of supporting complex life are not as common as many astronomers have believed.

Is it only astronomy that seems to be leading to the conclusion that Earth is rare?

Gonzalez:   No. The more inclusive discipline of astrobiology is tending that way. Astrobiology is really an interdisciplinary topic, which includes astrophysics, biochemistry, celestial dynamics, climatology, comparative planetology, life in extreme environments, among others. It is ironic that some astrobiologists would come to the position of our rarity, given that most in this field are motivated by the hope of one day finding intelligent life on another planet. About the only field that has produced evidence in the other direction is extremophile research. But, at the same time, we've learned that Mars, today, appears to be sterile, even though it probably got a helping of Earth's microbes early on via meteorite transfer.

Are you in complete agreement with Ward and Brownlee's hypothesis?

Gonzalez:   I am not in complete agreement with a couple of aspects of their version of the Rare Earth hypothesis.

First, I am more skeptical than Brownlee and Ward about the existence of simple life on other worlds. They seem to downplay the great difficulty origin-of-life researchers are having in understanding how life first arose from a naturalistic perspective.

Second, I believe the most important implication of this hypothesis is that the cosmos is designed. Brownlee and Ward conclude that their hypothesis should move us to have greater concern for the environment since "good planets are hard to come by." While I agree this is a worthwhile implication, it is hardly the most significant one.

There are just too many "coincidences" to believe that the Earth came about by chance — and so consequently it must have had a designer?

Gonzalez:   The case for this is becoming stronger every year. And, I have not yet mentioned all the examples of hyper-fine-tuning of the physical constants necessary for even one habitable planet in the universe. Add these, and the case against chance is extremely strong.

You've published a recent technical paper with Ward and Brownlee proposing the concept of a "Galactic Habitable Zone," as well as an article in Scientific American (October, 2001). What is the Galactic Habitable Zone?

Gonzalez:   The Galactic Habitable Zone (GHZ) is the region of the Milky Way galaxy — our galaxy — where habitable planets are most likely to exist. We've taken into account the elemental requirements for building habitable planets and the astrophysical threats to life. The elemental requirements set the outer boundary of the GHZ, while the threats set the inner boundary.

So if we imagine our galaxy as a big spinning disk, or pinwheel, solar systems with habitable planets have to be a certain distance from the center of the galaxy: neither too close nor too far away?

Gonzalez:   Correct. To build an Earth, you must have a sufficient concentration of heavy elements available. For astrophysicists, by the way, heavy elements are anything heavier than helium; so not only strontium, lead, and so on, are heavy elements, but also those elements directly essential to biological life, such as oxygen, carbon, and nitrogen. Heavy-element content varies widely in the galaxy. Stars forming close to the center of the galaxy are endowed with more heavy elements than our sun, while those outside our solar system's orbit have less. Since, as I said, the creation of planets around stars depends on having the right initial concentration of heavy elements, there should be few Earth-like planets in the outer regions of the galaxy, because sufficient heavy elements simply are not available there.

But a solar system with a habitable planet cannot form too close to the center of the galaxy either. A galaxy contains dangerous places, such as its center. The galactic-scale threats to life can be divided into two types: comet impacts and transient radiation events. The latter group includes supernovae, gamma-ray bursts, and outbursts from the vicinity of the giant black hole at the center of the galaxy. In addition, if we were closer to the galactic center, more comets in the outer reaches of our solar system would be perturbed easily by passing stars and other massive objects, so that they are more likely to "visit" the inner planets and threaten the Earth with impacts. All these threats are greater in the inner regions of the galaxy.

So if you take into account the threats in the inner galaxy, and, the radial gradient in heavy element abundance in the galactic disk, the net effect is a ring-shaped GHZ.

So, by comparison to the whole galactic "disk," the Galactic Habitable Zone is a relatively thin ring-shaped zone. Just to add some perspective, if the galaxy were a dinner plate with a diameter of 8 inches, then where would the GHZ be, and how wide would it be?

Gonzalez:   If the disk were a dinner plate, it would be a little less than a tenth of an inch thick. I can't yet say how large the GHZ is. At most, it contains about 10 to 20 percent of the stars in the Milky Way. This does not mean, however, that every star in the GHZ will have habitable planets! Obviously, we are inside the GHZ. We are located about half way out to the edge of the visible disk.

Have other astronomers simply overlooked all these amazing connections?

Gonzalez:   I am continually amazed by how poorly even astronomers understand the galactic-scale requirements for a habitable planet. For example, in 1974 Carl Sagan and Frank Drake transmitted a radio message to the Great Globular cluster in Hercules. It was a public-relations event, as they both knew at the time that a return message would not be expected for tens of thousands of years. What they did not seem to realize is that a globular cluster, even though it contains hundreds of thousands of stars, does not have sufficient heavy elements to build Earth-size planets, and even if you could form an Earth, the stars are packed too close together to allow stable circular planetary orbits. A globular cluster is the last place in the entire galaxy I would look for ETI!

You've recently come up with something even more daring. You believe that the Earth is not only rare, but is privileged as well. What do you mean by that?

Gonzalez:   One could say that the Earth is one of the privileged few planets that can host intelligent life, or one could say we are privileged as one of the few or only intelligent life in the universe. But there's more.

Starting in 1998, I noticed that certain phenomena are better observed on the Earth's surface than from other places in the solar system. I first noticed this with total solar eclipses. It turns out that of the nine planets and roughly 70 moons in the solar system, the Earth is the best place to observe total solar eclipses. The Earth also happens to be the most habitable place in the solar system. This suggested to me that perhaps habitability generally correlates with observability/measurability. So to test this hypothesis I looked at fields ranging from geophysics to cosmology, and I found many more confirming examples. I am in the process of writing up my findings in book form, with Jay Richards, of the Discovery Institute in Seattle.

I received a grant from the Templeton Foundation in 2000 to study the correlation between habitability and measurability. Our book will be the first fruit of that study, and I plan to follow it up with several research papers.

What do other scientists think of the possibility that the Earth is a Privileged Planet?

Gonzalez:   I have not yet discussed my hypothesis with many scientists; I want to wait until we complete our book. But I can say that the idea that we and our home planet are somehow privileged is repugnant to moderns. They seem to think that anyone who holds to this view is guilty of great hubris and arrogance.

I have a couple of responses to this. First, the truth of a claim is independent of any perceived hubris. Second, most scientists have imbibed deeply of historically revisionist fictions associated with the metaphysical Copernican Principle. As a result, any claim that puts the Earth on a pedestal is seen as a direct assault on the Copernican Principle, which is one of their central guiding principles.

What, then, does all this mean for Christians? What has it meant for you as a Christian?

Gonzalez:   If we are right, then ours is the strongest empirical evidence for purpose in the universe to date. And what purpose is it? It is simply that the universe was designed for scientific discovery by intelligent life. What better mandate could we have for the scientific enterprise than to discover that the universe is set up for it? Naturalism — what is often called "materialism" — does not provide an adequate basis for science.

For Christians, this will bring the long story of science full circle, back to its Judeo-Christian roots. It is still not widely known that the historical origins of modern science were largely Christian, and most of the great scientists of the past four centuries were devout believers. I view this last century-long dance with naturalism as a temporary malady.

As a lifelong Christian and a lifelong lover of scientific discovery, I see this discovery as a partial answer to my childhood questions. Since I was a child, my faith has supported my love for science and vice versa, and I was guided, in part, by an intuition that there was something profound about the cosmos that pointed towards God.

I have not yet discussed my hypothesis with many scientists; I want to wait until we complete our book. But I can say that the idea that we and our home planet are somehow privileged is repugnant to moderns. They seem to think that anyone who holds to this view is guilty of great hubris and arrogance.

I have a couple of responses to this. First, the truth of a claim is independent of any perceived hubris. Second, most scientists have imbibed deeply of historically revisionist fictions associated with the metaphysical Copernican Principle. As a result, any claim that puts the Earth on a pedestal is seen as a direct assault on the Copernican Principle, which is one of their central guiding principles.

What, then, does all this mean for Christians? What has it meant for you as a Christian?

Gonzalez:   If we are right, then ours is the strongest empirical evidence for purpose in the universe to date. And what purpose is it? It is simply that the universe was designed for scientific discovery by intelligent life. What better mandate could we have for the scientific enterprise than to discover that the universe is set up for it? Naturalism — what is often called "materialism" — does not provide an adequate basis for science.

For Christians, this will bring the long story of science full circle, back to its Judeo-Christian roots. It is still not widely known that the historical origins of modern science were largely Christian, and most of the great scientists of the past four centuries were devout believers. I view this last century-long dance with naturalism as a temporary malady.

As a lifelong Christian and a lifelong lover of scientific discovery, I see this discovery as a partial answer to my childhood questions. Since I was a child, my faith has supported my love for science and vice versa, and I was guided, in part, by an intuition that there was something profound about the cosmos that pointed towards God.