Billions of Planets, But Only One Earth

First, our planet was ousted from the center of the universe, then our sun was found to be only one of many suns in an immense galaxy; next came the discovery that our galaxy is just one of countless stellar systems in the cosmos.

Following upon these findings, one of the longstanding assumptions of modern science has been that, given the billions of stars in our galaxy and the billions of galaxies in the universe, there must be countless other planets out there teeming not just with life, but intelligent life at that. Human beings, on this assumption, would be nothing special. Carl Sagan once conjectured that, in our own humble galaxy alone, there must be a million civilizations of creatures intelligent enough for interstellar communication. This conjectured plurality of worlds and intelligent creatures seemed to threaten the central Christian doctrine of the Incarnation. If God himself is united to human nature in our world, how is he dealing with other intelligent creatures elsewhere in the cosmos? Does the Incarnation apply to them? Is it just a local phenomenon? C.S. Lewis wrote his famous Space Trilogy as an imaginative exploration of this very difficulty.

Now along come Peter Ward and Donald Brownlee to upset scientific orthodoxy and reinvigorate us monotheists. Earth, they claim, is no run-of-the-mill planet. We are "not so ordinary as Western science has made us out to be . . . . Our global inferiority complex may be unwarranted." Against the common view that we are all too common, they offer the rare-earth hypothesis the paradox that life may be nearly everywhere in the universe, but complex life almost nowhere. By "complex," they mean anything above the microbe. Furthermore, since the rarity increases as the complexity increases, "intelligent animal life must be rarer still." Earth, then, is not ordinary at all; indeed, it is quite extraordinary, and even more exceptional is the existence of intelligent life.

If the rare-earth hypothesis is right, human beings may be the most unlikely phenomenon in the universe. "If some god-like being could be given the opportunity to plan a sequence of events with the express goal of duplicating our 'Garden of Eden,' that power would face a formidable task," declare Ward and Brownlee. "With the best intentions, but limited by natural laws and materials, it is unlikely that Earth could ever be truly replicated. Too many processes in its formation involved sheer luck . ... [T]he physical events that led to the formation and evolution of the physical Earth ... required an intricate set of nearly irreproducible circumstances."

How so? Well, if you want any kind of life on a planet, you've got to have a sun, and not just any sun will do. It has to be the right distance from the center of the galaxy. If it's too close to the star-dense center, it will likely be sterilized by a supernova, an exploding star. If it's too far away, it will be too poor in heavy elements, the building blocks of a habitable planet. Your sun will also have to have the just right mass; otherwise, the planets orbiting it will be too close or too far away to sustain life. For these and other reasons, Ward and Brownlee declare, our rare earth required a rare sun.

Shall we add the presence of Jupiter? If you don't want your planet to be bombarded by comets and asteroids, you'd better have a "sweeper." Because of its great mass, Jupiter cleans interstellar debris from our solar system. Without it, the Earth would likely be continually pummeled and therefore lifeless. Let's also add that, if Jupiter were any closer to its sun, as other Jovian-type planets generally are, it would have crushed the Earth. Another happy accident!

We have a glimpse of how rare the conditions surrounding our planet are, but the conditions of Earth itself are rarer still. According to the authors, getting life, microbial life, might be relatively easy. Therefore, such non-complex life may very well be abundant in the universe. But complex life is both difficult to attain and maintain. To begin with, you need an atmosphere, surface water and a constant but narrow range of temperature. Attaining and maintaining these require an immensely complex dance of factors the right amount of initial carbon available, a molten core of the right elements and temperature, the presence of a sufficient magnetic field and other factors too numerous to mention.

In addition, if you want to maintain the conditions of life over sufficiently long periods of time, say, multiple millions of years, you have to avoid all kinds of catastrophes all too common on other planets. Earth, unlike many other planets, has managed to escape such destruction.

On top of all this, we, the Earth, actually have complex life, the existence of which is far, far more unlikely than the conditions which allow it. When we string together the list of all these improbable conditions and events, the authors claim, the probability of creating a planet with complex life approaches zero. The actual presence of Earth, given the extremely complex and interrelated conditions which allowed its birth and continuation, is near miraculous. Science, it would seem, is leaning back toward faith: We really may be the only rational animal in the universe after all.

In regard to Christian theology, the most helpful thing about the arguments of Ward and Brownlee is that they are not trying to be helpful at all. They show no evidence of being Christian, or even being vaguely theistic, but argue from the perspective of evolutionary-based scientific materialism. No one can accuse them of stacking the deck in our favor. The cards are dealt by nature itself.

Read this book if your experience of the faith has become rather perfunctory and you could use a shot of awe and wonder over our creator, God. He's in here, if only between the lines, on every page as sure as he's in the heavens.