U-M Heritage

JFK at the Union

Legend has it that John F. Kennedy first proposed the Peace Corps at U-M. The truth is more complex, and a lot more interesting.

Most emailed stories

• Exactly how much housework does a husband create?
• U-M Heritage: How to date women, circa 1943
• University of Michigan 2008 Graduation (Story and Video) | Michigan Today

Talking about science

Look where it's lively

Want to find alien life forms? You'll need to search where even non - living things are active.

Talking about words

Us and them

Are you a fudgie? A chicken - necker? Maybe a dingbatter? It all depends on where you go — and who you aren't.

Talking about movies

Tying Hitchcock to the stage

Our film critic's favorite Hitchcock movie has come to Broadway. But how do you fit a hurtling train onto a stage?

Video

Attacking nuisance algae

The stinky slime of algae can make any lake unbearable. U-M prof John Lehman is developing new ways to do something about it.

Michigan Today is a monthly online magazine for alumni and friends of U-M.

Letters to the editor

Your U-M history

Alumni notes

Alumni Books and Arts

Archives

U-M Events

Update your contact information

Unsubscribe

Contact Us

Talking about science

Look where it's lively

By Tim McKay

Arthur Thurnau Professor of Physics and Astronomy

January 15, 2008

email | print | respond

This summer we found a puddle that was alive. It's not what you're thinking. Not some leafy vernal pond you might find in a Michigan wood, wriggling with tadpoles and larval newts. This was a regular puddle; a pool of muddy meltwater gathered on the granite of a Canadian mountaintop, way above the treeline. As we hiked by, the wet-blanket mist broke, admitting a glaring high altitude sun. The water in the puddle was cloudy with mud, impenetrably iron-red, and alive with swarming motion.

We watched, and flows emerged; intersecting, breaking apart. It was entrancing, like a school of minnows or a clutch of ducklings, and it drew us in. Crouching down, we stared from every side. What was in there? How could this little puddle, alone among ice-broken boulders, be so full of life? The sun came and went, and we gradually realized this was less than it seemed. No little swimmers paddled our lively puddle into motion. Blasts of energy from the sun, heating different parts of the puddle unequally, drove it into mad action. This puddle was lively, but it wasn't life.

For me, no discovery could be more important than to find life in different places

The more you think about it, the more difficult it is to discern the boundary between the alive and the merely lively. Imagine the Earth devoid of life. Convection in the Earth's mantle would continue to shuttle the continents across the globe, building magnificent mountain chains. Water would still rise from the seas, build thunderheads, and inexorably tear down them down. This lifeless blue planet would remain an awfully lively place. Many of the other things we associate with life happen freely in the non-living world. Structures form of their own accord. A bit of water vapor releases heat energy to its colder surroundings, settling in the process into a fantastically beautiful snowflake. New things appear, grow, and pass away. Heat from the ocean rises through the atmosphere, torquing up a monster hurricane that carries its violence ashore before dying away. If all this happens without life, what is the dividing line?

It seems the experts have largely given up trying to figure this out. The Oxford English Dictionary collapses into circularity, calling life "The property which constitutes the essential difference between a living animal or plant … and dead or non-living matter." Life is the property which makes things alive. They neglect to say what this "property" is, but I guess they know it when they see it. One commonly adopted practical definition calls living things those which use resources from their environment to reproduce themselves. Bacteria and fungi are in, but viruses are out. This definition is useful, but also open to disturbing counterexamples. Is a fire alive? What about a tornado? If a mule can't reproduce, must we consign it to the non-living? Other proposed definitions suffer from similar weaknesses.

Part of the challenge, clearly, is that all the myriad forms of life on Earth share the same basic framework, including the same DNA-based scheme of reproduction. It's quite likely that all descend from a single origin. Can we scientifically understand the nature of "living" things, when we ultimately have only one example to consider? The job for scientists at this point is clear. It's time to find more life. For me, no discovery could be more important.

Fortunately we know where to look. The puddle at the start of this essay provides the key clue; to find life, look where things are lively. Life may be no more than an exciting and interesting application of physics and chemistry, but it is surely no less. It feeds on the same flows of energy which drive all interesting non-living processes too. You can only find them together, just as you do on the Earth.

So where might we find new flows of energy on which both liveliness and life might subsist?

•  Molten cores: One new possibility has emerged that is literally beneath our feet. The core of the Earth is heated by radioactive decays of heavily elements trapped when it was formed. Energy from this inner glow, emerging from below, fuels life in the deep oceans. Take away the Sun, and this flow of heat would remain, providing, perhaps, enough to keep life cooking. Planets heated by this sort of radioactive glow, even if far from any star, might simmer with life beneath their surfaces.
• Other planets: On the Earth's surface, action is driven by the flow of energy from the Sun. This flow powers weather and the water cycle. It also enables life. So the traditional place to seek life is on planets with surfaces heated by nearby stars. There is a Goldilocks problem though. The arrangement has to be just right, not too hot and not too cold. Within the solar system, only the Earth will do.
• The first extra-solar planets were discovered only a dozen years ago. Now almost 300 have been found, and the pace of discovery is accelerating.  Unfortunately, we have no technology for traveling to another star in less than a lifetime.  We will search from afar. But life, something we can’t even properly define, is going to be hard to definitively identify from a distance of many light years. I’m not betting we'll find it in our lifetimes.
• Tormented moons: Closer to home, in our own solar system, a more exotic flow of energy exists in moons of the outer planets: tidal heating. Io and Europa, orbiting Jupiter, provide an example. Io swings around Jupiter every 42 hours or so. A little farther out, Europa takes just about twice as long. Every time Io passes between Jupiter and Europa, it is tugged outward a little. Trapped in this struggle, Io is repeatedly stretched and squashed by the varying tug of Jupiter's gravity. This cyclic stress heats it, just as you might warm a ball of clay by working it with your hands. In this case the effect is extreme, making poor little Io the most violently volcanic body in the solar system. Europa, too, is heated in this dance, enough to maintain a 60-mile-thick ocean of liquid water beneath a deep layer of ice. The same process is active in the moons of Saturn as well, most spectacularly on Enceladus, where dramatic plumes of water vapor were discovered spewing from this tiny moon's South Pole in 2005.

I find these discoveries incredibly exciting, because these places all possess the kind of long term energy flows that power liveliness. We know they've got some remarkable non-living processes going on. Maybe one of them crosses the line (wherever it is) and hosts real life. Maybe they all do.

As winter settles in over Ann Arbor, and life here seems to disappear, that lively puddle in the Canadian Rockies returns from the recesses of my mind, an odd symbol of hope. One day, we'll find some pocket of liveliness in the Solar System that contains something more; little squigglers that use the available flow of heat to make new squigglers, new life. My greatest scientific wish is to be around when it happens. I hope we get to see it together.

 

Back to top

Tim McKay grew up in Michigan, in love with the natural world. He studied physics at Temple University and the University of Chicago, and now teaches it to anyone who will listen.

McKay joined the University of Michigan faculty in 1995, where he is currently Arthur Thurnau Professor of Physics and Astronomy.