Our Planet Is Teeming with Life; Does That Mean the Universe Is Too?

(A moose in Grand Teton National Park)

While on a recent drive from Idaho to Colorado, I was struck by something so amazing and yet so ordinary that, for most of us, it’s hardly worth mentioning—something we take for granted in our day-to-day lives and yet is all around us, intertwined with almost every experience we have.

The insight was this: our planet is teeming with life! As I drove down the small two-lane highway, I couldn’t help but notice the countless varieties of grasses, wildflowers, and trees, each shooting up majestically toward the sky according to its own kind’s height tolerances. And, of course, there were critters and megafauna of all sorts as well, both wild and domesticated: birds, ground squirrels, and antelope of the wild variety, and cattle, llamas, and alpacas of the domesticated variety.

No matter where you go on Earth, there is life, from the depths of the ocean to the arctic tundra, from the highest mountaintop to the bubblingest and boilingest geothermal vents. And while we still don’t understand the precise conditions needed for life to arise from nonliving matter, it’s clear that life on our planet has flourished and has proven to be most robust, even when faced with the most seemingly inhospitable of environments.

One of the biggest questions in astrobiology is whether life is frequent or rare in the universe. Are the conditions necessary for life to originate so specific that life is unlikely to have arisen anywhere else besides Earth, or perhaps in very few other places? Or is life so easy to generate that the universe is teeming with life just as much as our planet is, at least on the millions and millions of presumably Earth-like planets in their stars’ habitable zones?

As I drove along the twists and turns of the Wyoming mountain pass between Idaho and Colorado, I couldn’t help but think that the ubiquity of life on our own planet demonstrates that not only that Earth is hospitable to life but that the universe as a whole must be hospitable to life. At the risk of making an unjustified leap of logic in the form of a hasty generalization from the lone datapoint of life on Earth to the inevitability of life elsewhere in the cosmos, it seems to me that the diversity of life on Earth and the corresponding diversity of the environments in which Earth’s many lifeforms are found makes it likely that life will be found in millions and millions of nooks and crannies in the universe, in anyplace analogous to the homes of Earth extremophile life forms, from the vast oceans beneath the ice of Europa to the primordial ooze of amino acids on some neighboring exoplanet.

It saddened me a bit along the drive that I will likely not live to find out the answer to this fundamental question of astrobiology: whether life elsewhere in the universe is nonexistent, as common as life on Earth, or far rarer than the most precious jewel. And yet, I can’t help but think that humanity will know the answer to this question one day, if only in the far future when all that’s left of me are these words and my long-decayed remains beneath the ground, from which new life will eventually spring as well—itself a lovely poetic thought.

The Drake Equation

(The Drake equation provides a quantitative framework for calculating the likelihood of finding and communicating with intelligent lifeforms elsewhere in our galaxy.)

Scientists of all sorts love their equations, and astrobiologists are no exception. The favorite equation of astrobiologists is the Drake equation, which is supposed to provide a means for calculating the probability of finding and communicating with intelligent lifeforms elsewhere in the our own galaxy, taking into account as many of the relevant variables possible, such as the rate of star creation in our galaxy, the fractions of those stars that have planets, the percentage of those planets that are likely to support life, and so on.

For reference, here is the Drake equation and a key to interpreting the many variables it contains:

The Drake Equation: N = R_∗ · f_p · n_e · f_l · f_i · f_c · L

• N = The number of civilizations in our galaxy with which communication might be possible
• R_∗ = The average rate of star formation in our galaxy
• f_p = The fraction of those stars that have planets
• n_e = The average number of planets that can potentially support life per star that has planets
• f_l = The fraction of planets that could support life that actually develop life at some point
• f_i = The fraction of planets with life that actually go on to develop intelligent life (civilizations)
• f_c = The fraction of civilizations that develop a technology that releases detectable signs of their existence into space
• L = The length of time for which such civilizations release detectable signals into space

(Source: The Drake Equation, The SETI Institute)

The problem, of course, with the Drake equation is that the values of most, if not all, of the variables (except perhaps the rate of star formation in our galaxy) are unknown. Nonetheless, the Drake equation provides a useful framework for thinking about the factors that are relevant to the presence of life in general, and intelligent life in particular, elsewhere in the galaxy besides on our own planet, no matter how ubiquitous life is here on Earth.

Still, despite the fact that attempts to formulate the question mathematically are relatively fruitless until we begin to fill in the relevant data points empirically, which may take hundreds, thousands, or even millions of years, I can’t shake my intuition that if life is so common here on Earth, and if there is nothing special about the laws of physics here on Earth, then the conditions for life to arise must have been duplicated countless times elsewhere in the galaxy and in the universe as a whole. It thrills my imagination beyond words to think of a universe full of lifeforms, sentient or not, and however similar or dissimilar to the life forms we are used to on Earth with their seemingly endless varieties and species-specific ways of being.

Prescientific intuitions, however, aren’t science, and real scientific inquiry and discoveries must naturally take precedence over philosophical intuitions formed in a vacuum—or on our own planetary and cosmic oasis. Yet it would strike me as very strange indeed if our planet Earth were such an oddity, such a rarity, such an unlikely place to find life that life arose nowhere else in the universe besides here. That means, of course, that there may be millions upon millions of life forms out there in the universe right now, from the lowliest extraterrestrial equivalent of a bacterium to the most advanced alien civilization asking the very same questions about our existence as we are asking about theirs. If so, then we hopefully are friends in the making, just waiting to find each other and to make the emptiness of the space between our worlds seem a little less empty for the effort.

For Further Reading:

• The Drake Equation: Estimating the Prevalence of Extraterrestrial Life through the Ages, edited by Douglas A. Vakoch and Matthew F. Dowd, with forward by Frank Drake

The Drake Equation by Douglas A. Vakoch and Matthew F. Dowd