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Mother Nature’s Red and Blue Clock

Posted by | August 5, 2009

I worked for three years as a reporter for a daily newspaper. I loved the deadlines. I remember well the intensity of running down the courthouse hallway after the jurors who had just rendered the verdict in a murder trial. I’ll also confess to speeding after fire trucks to the local airport during an emergency there.

That’s one sense of time, familiar to compulsive coffee drinkers, manic single moms, and frantic business people everywhere. But let me offer you another sense of time, one that unfolds over epochs and eons and that might give you a new appreciation of nature.

Each Sunday I walk my dog along the railroad tracks that parallel the Snake River at the bottom of the Snake River Canyon. Clearly, the canyon was created as the river eroded the rock, bit by bit, over vast stretches of geologic time. But how do geologists get their heads around just how much time is involved in events in Earth history like the formation of everything from huge canyons to volcanic rocks or fish fossils?

The answer usually depends on natural “clocks” that are imbedded in Earth materials. We geologists have learned how to read the hands of those clocks, and you can, too.

Radioactive decay is the main clock Mother Nature offers us. That can sound a bit scary, perhaps, but what’s at issue can be explained in terms of a simple game I’ve played with college freshmen or even younger students using red and blue bubblegum balls.

Imagine you are given a bowl with 16 red bubblegum balls in it and a supply of blue and red gumballs to the side. The rules of the game are that, every minute on the minute, you remove half the red gumballs and replace them with blue gumballs.

Here’s how things will go: You start with 16 red gumballs and no blue ones. After one minute, you replace half of your 16 reds with blues, so you have 8 reds and 8 blues. After the next minute, you replace half your reds again, so you have 4 reds and 12 blues. After the next minute, you’ll have 2 reds and 14 blues. After the next minute, you’ll have 1 red and 15 blues.

Here’s the most interesting part:

If I brought my Uncle Harry into the room at some random time after the game started, he could deduce how long you’d been playing. For example, if you had 2 reds and 14 blues in your bowl, Uncle Harry could figure out the game had been running between 3 and 4 minutes.

The gumballs are a simple analogy of radioactive elements and how we geologists can tell time based on them. The red gumballs represent the “hot” or radioactive elements (like carbon-14, a substance you hear about in the news sometimes.) The blue gumballs are the stable atoms the radioactive ones become over time as radioactive decay proceeds. Each minute in our example is called a half-life. Those are just the rules of the game that Mother Nature set up.

To be honest, I’ve had students eat a couple of gumballs out of their bowl somewhere in mid-game, and Mother Nature sometimes lets reds and blues “leak” out of sample materials.  Those are complications, but there are ways to adjust the mathematics if they occur.

We geologists determine the ages of ancient bits of wood or volcanic minerals by finding the proportion of red and blue atoms (so to speak), and calculating how long the natural process of radioactive decay has been going on. The reds and blues are the natural “clock” that gives us a way to calculate just how long ago the Ice Age was or when the last dinosaur roamed North America.

I still like short deadlines, but Mother Nature often operates differently. She’s got lots and lots of time for her stories. Lots of time is part of what makes the complexity of the fossil record and the world’s vast canyons possible. They are a richly detailed tapestry woven over deep amounts of time.