The Difficulty of Defining Life

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“How do you reply to a 13-year-old who says he doesn’t understand the Trinity?”

A snarky pastor asked that of my wife during her ordination examination. The pastor apparently felt it was a rite of passage for the soon-to-be ordained to address such questions on the floor of Presbytery.

After a brief pause, my wife leaned toward the mic and said, “Well, I’m 28, and I don’t understand the Trinity either.”

As we continue our series about life on other planets, we will see that the Trinity shares something in common with life—they’re both hard to define. My wife’s response could very easily mirror a young scientist’s response to a question about the nature of life.

The Enigma of Life

What is life? Well that’s complicated. In a 2015 talk, Br. Guy Consolmagno summarized forty-eight descriptions of life in just shy of an hour. At the end of the day, there is no really satisfying answer.

Life is complex. It has material and seemingly non-material aspects. It can’t just be reduced to DNA and reproduction, but it certainly includes them. Death is even factored into the definition of life—assuming we know what death is. Biology, chemistry, physics, and new sciences like complexity and information all are part of the equation. And that does not begin to consider ideas about meaning, purpose, value, and other seemingly less scientific aspects.

From another angle, though, life is simple. To date, we have exactly one example of life—the kind we find here on earth. It is carbon-based, requires water, with key replicating molecules like DNA and RNA that make proteins. It requires a set of just right conditions of temperature, atmosphere, and energy sources. For this reason, basic biology, especially origins of life research, features prominently in astrobiology. It is how we know what to look for when searching for life.

The search for extreme life and non-carbon-based life are also key aspects of astrobiology. On Earth, life exists in some pretty extreme conditions—like hot ocean vents. We are also beginning to search for life built on elements other than carbon. Maybe methane can replace water. Whether we find such life forms on Earth or build them synthetically, knowing about them and how they work will only expand the range of possibilities we can search for out there in the universe.

Finally, there is a largely ignored world of what some have called biological dark matter—poorly understood genetic material here on Earth. While this matter may or may not be extreme life, knowing more about it will increase our understanding of life on Earth and, as a result, what to look for beyond it.

  • Astrobiologist turned priest Lucas Mix considers the nature of life.

The Meaning of Life

A few years ago, the Center for Theological Inquiry—with the help, surprisingly, of NASA funding—hosted a cohort of theologians and humanities scholars to consider the implications of astrobiology. A member of the cohort was Lucas Mix, a Ph.D. biologist and Episcopal priest who literally wrote the book on astrobiology. He kicked off the CTI discussion with a blog in which he playfully paraphrased Psalm 8:

What is life that you are mindful of it—alien life that you look for it?

Mix elaborates on how our quest to define life—and seek it elsewhere—can enrich our lives. Though we only know of one kind of life—carbon-based, water-reliant, utilizing reproduction and DNA—does not diminish the value of this pursuit.

“[Astrobiology] gives us an opportunity to reflect on our own life, what it means to live fully, and how we think about living in community—or living alone,” Mix writes. “I, for one, hope that life ‘out there’ will help us discover the meaning of life here. The search has already told us more about ourselves, and the world we inhabit, than we ever could have asked or imagined.”

The search for life “out there,” whether or not we find it, can be relevant today. When we consider science and the meaning of life, we ask one of the great questions of any age.

Who are we, mortal biological creatures, O God, that you are mindful of us and care for us?



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