Radiometric Popcorn

A couple of years ago, a friend on the Sonlight Forums, asked this in a thread she created about the age of the earth:

"I guess my biggest question would be about Carbon-dating. I'm guessing that this is a major factor in determining the age of the earth? So how can we know if this is fact or fiction?"

Having been asked that a number of times, and always struggling to come up with a way of discussing radiometric dating in a way that would effectively introduce the basic concepts for those without a lot of background in that area of science, I came up with the following response:

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Let's just take very small steps here. I'll just offer a single step, and when I've got you both nodding that you're comfortable, we'll move on. OK? First let's get a handhold on radioactive decay. The example I want you to consider is a bag of microwave popcorn. You start with an unpopped bag, and at the start all of the kernels are "unpopped" kernels. Now, when you put it into the microwave and wait for a couple of minutes, you will hear the "pop, pop, pop" of kernels popping into "popcorn". At first, just a few kernels have popped. But over the next minute or so once the popping starts, most of the "unpopped" kernels pop into "popcorn". Hopefully, by the time your microwave timer goes off, you will have a bag that has almost completely converted from "unpopped" to "popped" popcorn. It you are rolling your eyes at me here, that's fine, pretty basic so far. But I think this is a good starting point for visualizing and understanding what is happening with radioactive decay.  Now. We are going to switch from a regular bag of microwave popcorn to Radiometric™ Brand Popcorn -- a special kind of popcorn that works like a radioactive specimen that is decaying. With Radiometric™ popcorn, you do not need to put it into a microwave to get it to pop. In fact, you cannot do *anything* to it to keep it from popping. Radiometric™ brand popcorn pops at an even rate, all the time, no matter what, forever. Moreover, Radiometric brand popcorn pops at a predictable rate, according to a rule: Radiometric™ popcorn pops half of its remaining "unpopped" kernels into "popped" popcorn every day.  This is very important to understand. If we bring home a bag of Radiometric™ brand popcorn on Tuesday at noon, and our bag has 10,000 unpopped kernels at that point, we will find only 5,000 unpopped kernels when we check it on Wednesday at noon - 5,000 kernels (half of what we had at noon Tuesday) will have popped. If we check our bag again on Thursday at noon, we will see that half again of what we had has popped: 2,500 kernels have popped since Wednesday at noon. In order to make this easy to see, here's a list of our daily counts for our Radiometric™ brand popcorn kernels for the first week: Counted At Popped Total Unpopped Tuesday Noon 0 10,000 Wednesday Noon 5,000 5,000 Thursday Noon 7,500 2,500 Friday Noon 8,750 1,250 Saturday Noon 9,375 625 Sunday Noon 9,687 313 Monday Noon 9,844 156 Tuesday Noon 9,922 78 So, a week later, you would find that your bag of Radiometric™ popcorn which started with 10,000 unpopped kernels has almost completely popped -- converted into popcorn -- with only 78 out of 10,000 kernels remaining unpopped. And remember the rule: however many unpopped kernels yo have in the bag of Radiometric™ popcorn, you can depend on there being precisely *half* that many remaining unpopped twenty for hours later. It is rock-solid dependable, like a clock (because it is a clock!). Now if you've followed me this far, we are well on our way! For Radiometric™ popcorn, the "half-life" is "24 hours"; as I said above, and you can see in the numbers in the table, every 24 hours, half of the remaining unpopped Radiometric™ popcorn pops.  I'll wrap up with this: if you have bag of Radiometric™ popcorn that you know had 10,000 unpopped kernels in the bag at noon on Tuesday when you bought it, you can make some accurate and reliable assertions later on if you are to look in the bag and count the unpopped kernels. If your son tells you he can't remember when he last cleaned his room, but it was when his sister had just finished counting and found only 100 unpopped kernels left in the Radiometric™ popcorn bag, then you can know with confidence that your son cleaned his room sometime on Monday after noon. The predictable, uniform rate of "popping" of Radiometric™ brand popcorn demonstrates the process of isotope decay.