December 16 – Carb-gone 14

Today’s fasctismal: The oldest age that carbon-14 can give is 114,600 years; the youngest is 570 years.

If you have ever cleaned up a teenager’s room, then you have probably discovered one of the most fundamental tools of archeology: relative dating. (You’ve also discovered what it feels like to excavate a midden pile.) As you dug down through the layers of trash, petrified food, and old homework assignments, you probably noticed that the older stuff was on the bottom and the newer stuff was on the top. But what might surprise you more than the Wall Street Journal hidden under your child’s bed is the fact that until 1949, relative dating was about the only method that archeologists had for dating really old artifacts.

A household in Pompeii (My camera)

A household in Pompeii; we know how old this is thanks to records the Romans kept
(My camera)

That’s because very few artifacts come with a date on them. And even those that do come with an identifying mark, such as coins, only give you an approximate range of dates; for example, a coin with Julius Caesar’s face on it was probably minted sometime between 50 BCE (when he conquered Gaul) and 44 BCE (when his political opponents put a permanent end to his ambitions). And the older something is, the less likely it is to have any sort of identifying mark; an empty, twelve hundred year old clam shell from the Spiro Mound looks an awful lot like an empty, fifteen thousand year old clam shell from Siberia.

This coin provides an approximate date (Image courtesy Australian Centre for Ancient Numismatic Studies)

This coin provides an approximate date
(Image courtesy Australian Centre for Ancient Numismatic Studies)

Archeologists have come up with several methods for working around this problem (e.g., by counting tree rings), but they fail more often than not (after all, how many tree rings are there in a clay pot?). They needed something more. They needed a method that would work on almost everything and that could be easily verified. And, in 1949, a chemist by the name of Willard Libby gave it to them. He realized that by comparing the amount of carbon-14 that was in an object to the amount of carbon-12, he could tell how old something was. But, because carbon-14 had a half-life of 5,730 years, it could only be used to measure things that were between 0.1 and 20 half lives; that is, things that were no younger than 570 years old and no older than 114,600 years old.

But how does carbon dating work? I’ll give you an experiment that you can do at home to understand this basic concept (Teachers: This works really well in a large class if you ad up everyone’s numbers.). To do the experiment, you’ll need 84 pennies, 16 nickles, and 16 dimes. We’ll pretend that the pennies are atoms of carbon-12; because carbon-12 is stable, it doesn’t decay. A carbon-12 atom today will still be a carbon-12 atom 100,000 years from now. And we’ll pretend that the dimes are carbon-14 atoms. Carbon-14 is unstable; in 5,730 years, half of the carbon-14 that is present today will decay into nitrogen-14. (We never run out of carbon-14 because it is always being created by cosmic rays hitting nitrogen-14 in the atmosphere and turning it into carbon-14.)

When a critter dies, the ratio of carbon14 to carbon-12 is fixed

When a critter dies, the ratio of carbon14 to carbon-12 is fixed

Now a living thing will take in carbon-12 and carbon-14, so the proportion of the two atoms will be roughly the same as is in the atmosphere. But once it dies, it stops adding new carbon. As a result, when the carbon-14 decays it changes the ratio of the carbon atoms. To see that, we need to do our experiment. Start by placing the pennies in a pile and lining up the dimes, all heads up. (If you want, you can draw a dead critter around the money.) This is what the ratio of carbon-14 to carbon-12 looked like right after the critter died. There were 84 pennies/carbon-12 atoms and 16 dimes/carbon-14 atoms. (This was a very small critter.)

After one half-life about half of the carbon-14 has turned into nitrogen-14

After one half-life about half of the carbon-14 has turned into nitrogen-14

Since we don’t want to wait 5,730 years for the atoms to decay naturally, we’ll flip the dimes, one by one. If the dime comes up heads, put it back in the critter because it didn’t decay. But if it comes tails, the carbon-14 atom decayed and turned into nitrogen-14 (aka, a nickle). You’ll probably have about eight of the dimes decay, so your new ratio will be 86 pennies/carbon-12 atoms to 8 dimes/carbon-14 atoms. Now flip the dimes again, once more replacing those that come up tails with nickles. Odds are that you’ll lose about 4 dimes this time and your ratio will be 86 pennies/carbon-12 atoms to 4 dimes/carbon-14 atoms. Do it again and you’ll get something close to 86 pennies/carbon-12 atoms to 2 dimes/carbon-14 atoms.

After two half-lives half of the remaining carbon-14 has turned into nitrogen-14

After two half-lives half of the remaining carbon-14 has turned into nitrogen-14

As you can see from the experiment, the ratio can tell you when a critter, such as a possum or a palm tree, died. And if that critter was then used to make something else, such as a shoe or a house, then we know about when the something else was made. So all you have to do to find out how old something is is measure the ratio of the carbon-14 to the carbon-12 in it. Pretty nifty, huh?

After three half-lives half of the remaining carbon-14 has again turned into nitrogen-14

After three half-lives half of the remaining carbon-14 has again turned into nitrogen-14

But I’m willing to bet that your ratios didn’t exactly match mine. That’s because we only used a very few atoms; in most living things, there are quadrillions of carbon atoms instead of just 100. But there are still some variances in the ratios because radioactive decay happens randomly. As a result, most carbon-14 ages have an error of about 3-5% (i.e., a 570-year old sample is probably somewhere between 540 and 600 years old).

So that’s our experiment on carbon dating. And now that you are a fully-qualified archeologist on par with Indiana Jones, why not start doing some real archeology by becoming a Digital Volunteer at the Smithsonian? You’ll look at old documents, type what you see, and help preserve historical records dating back hundreds of years! To learn more, flip over to:
https://transcription.si.edu/

September 28 – Oh, Baby!

Today’s Factismal: When a baby smiles with its teeth apart and showing, the baby is frightened. When a baby smiles with its teeth hidden, the baby is happy.

The human smile is a puzzling thing. We know that we do it when we are happy, but why do we do it? And why do we smile with our teeth together when most other primates smile with them apart? And when does this behavior start? Is it programmed into us by society or is it more intrinsic?

These monkeys aren't mad - they are playing (Image courtesy Psychology Today)

These monkeys aren’t mad – they are playing!
(Image courtesy Psychology Today)

It turns out that when a typical primate smiles with its teeth apart and gums pulled up to show off the teeth, it is usually (but not always) showing aggression. And when it smiles with its teeth together or the lips down to hide the teeth, it is showing submission. The only exception to this behavior appears to be what primatologists call “rapid facial mimicry” and what parents call “making faces”. Two or more primates will grimace at each other, trying to match the other’s face, as a way of becoming better friends. (No word on if their faces ever freeze that way.)

This baby is having a good time - or is he? (Image courtesy Baby Laughter Project)

This baby is having a good time – or is he?
(Image courtesy Baby Laughter Project)

Being primates ourselves, humans exhibit many of the same behaviors. But society always adds a veneer of confusion onto the basic data, which is why scientists who study the evolution of human behavior like to watch babies – they haven’t been as influenced by social norms and show a purer response. And they’ve found that human babies tend to follow the primate rule: teeth together and gums hidden, happy baby; teeth apart and gums showing, unhappy baby. And it isn’t just babies that follow these rules; the same pattern has been observed in blind people who have never had an opportunity to see others smile.

Of course, babies do more than smile; they also laugh. And that’s another rich field for research (and a little squee). If you happen to be the parent of a young baby, then the folks at the Baby Laughter Project would like your help in finding out why babies laugh and what that tells us about how our brains develop. If you’d like to help (or just want to watch videos of laughing babies), then head over to
http://babylaughter.net/

September 15 – Making the Tardigrade

Today’s factismal: The water bear has inspired a new type of glass.

If you have a crazy uncle (and who doesn’t?), odds are you’ve heard him say something like “Why do we spend so darn much on science? It never does nothing for us nohow!” Fortunately, it isn’t very hard to show your uncle where he’s wrong. For example, researchers have found new antibiotics from bacteria living in mud, have reduced the death rate to all-time lows using vaccines, turned fatal diseases into manageable problems, and found ways to speed shipping. And most recently, they have found a way to turn a tardigrade’s protective system into a stronger and clearer form of glass.

A tardigrade on a Q-tip (Image courtesy Darron Birgenheier)

A tardigrade on a Q-tip
(Image courtesy Darron Birgenheier)

What is a tradigrade, you ask? Why just one of the most amazing critters on Earth (or off of it). These little “water bears” shuffle about on moss, sucking the sap and being generally awesome. Also known as moss piglets, they have eight legs, a sharp snout, and an amazing ability to adapt. They are found in the depths of the ocean, on the highest mountains, in hot springs at 150°F, and below freezing ice. They can even go into a type of suspended animation when things get too extreme and come back to life when things get better later on.

A tardigrade getting along swimmingly (Image courtesy Tommy from Arad)

A tardigrade getting along swimmingly
(Image courtesy Tommy from Arad)

And that last trick was the clue that led to a new form of glass. When tardigrades go into suspended animation, they shed almost all of their water which mixes with proteins and other things on their outer shell and turns into a glasslike molecule that shields them from the environment. When researchers saw that, they decided to see if they could replicate the trick using ordinary glass. By depositing one thin layer of molecules at a time, they were able to build a glass that has a regular structure and some pretty irregular (for glass) properties. It was able to transmit light more efficiently, making it ideal for lasers and leds and solar cells. And it was stronger, making it ideal for screens and surgical tools. And all of this came about because some scientists looked at a tardigrade and asked “why can’t we do that?”

So the next time someone asks you what use science is, point to the handy tardigrade (assuming you can find one) and say “ask it!”

October 18 – Winner By A Landslide

One of the amazing things about science is how often things at one scale apply at another as well. For example, you can measure the way that a cup of lye reacts with a cup of water and know how much heat will be produced if you use a ton of lye and a ton of water instead. Or you can simulate an earthquake using a piece of spaghetti and that will teach you something about how the San Andreas behaves. Or, as Peter and Mary are about to discover, you can use a pile of rice to discover why the Earth is round.

 

The images on the television were both frightening and fascinating. There had been a heavy rainfall in California and the runoff was rapidly eroding the base of a cliff, causing parts of the cliff to collapse in large chunks that splashed mud and mayhem when they fell. That would have been fascinating enough but on top of the cliff were several multi-million dollar mansions that were following the formerly stable cliff on its downward plunge.

“Wow!” said Peter as he watched a particularly large chunk of a swimming pool fall twenty stories into the surf below. “That was amazing!”

“Yes,” agreed Mary. “I’m glad that they got all of the people out. But what about their stuff?”

“I guess they’ve got insurance,” Peter replied. “But why did they build on the cliff?”

“Probably for the view. But what I want to know is why isn’t the cliff still still standing?” Mary puzzled. “It was doing OK before the rain, so why fall now?”

“I dunno. Who could we ask?” Peter wondered.

“Well, Mr. Medes is on vacation this week, so we can’t ask him,” Mary said. “And your mom is an astronomer, so she wouldn’t know. That just leave my dad. But he’s an engineer. He probably won’t know either.”

“Well, there’s only one way to find out,” Peter said. “Let’s go ask him!”

With that the two young scientists left the den where they had been watching television and sought out Mary’s father. Since it was Saturday, the first place they checked was the kitchen; in addition to being a popular engineering professor at the local university, he was also an amateur gourmet chef who liked to make special meals on weekends. Sure enough, he was in front of the stove, cooking raw rice in oil and fragrant spices.

“Oh, boy!” Mary exclaimed. “Costless Rican Rice again?”

“You betcha!” her father replied. “I wanted to use up the last of that roast chicken and we had enough vegetables to make this interesting. Peter, would you like to stay for dinner?”

“I’ll ask my mom,” Peter said as his belly rumbled in response to the smell of the cooking. Mary’s father laughed at the sound.

“It sounds as if your stomach has already decided the answer will be ‘yes'”, he said as he stirred the rice. “So what may I do to help you two? Or are you just drawn to the sight of a master turning leftovers into a meal fit for a king?”

“We had a question about cliffs,” Mary said. “Why do they fall down?”

“That is an excellent question!” Her father boomed in response. “And I’ll tell you the answer just as soon as I toss these odds and ends into the rice.”

With that, Mary’s father scrapped chunks of cooked chicken and vegetables that were left over from the previous week’s meals into the rice. Pouring in a carefully measured amount of water, he gave the mass a final stir and put a lid on top. He then turned the heat down and turned to his daughter and her friend.

“So you want to know why cliffs fall down,” he said. “Why do you ask?”

“Well, we saw these cliffs in California that were falling apart and dragging the houses that were on top of them into the mud,” Mary said. “But the cliffs were only about two hundred feet tall. We’ve got skyscrapers that are ten times as tall. So why do the skyscrapers stand up and the cliffs fall down?”

“It turns out that you have come to exactly the right person to answer that question,” her father replied. “Though Peter’s mother might have done just as well; this applies to her field as well.”

“It does?” Peter asked. “How?”

“You’ll see!” Mary’s father replied. “To start with, we’ll need a couple of plates, some toothpicks, and some uncooked rice.”

Mary quickly went to the pantry and grabbed the things that her father had listed off. Her father took the plates from her and placed on in front of each of the scientists. He then gave them each a toothpick and poured a cupful of rice onto each plate.

“In front of each of you is a pile of rice,” he said. “What I want you to do is to make the tallest cliff of rice that you can by scraping away the rice at the bottom of the pile with the toothpick. When you are done, what do you think the cliff will look like?”

“It will be just like a real cliff,” Peter confidently said. “It will go straight up.”

“I’m no so sure,” Mary countered. “I think it will be a lot slope-ier. It will probably lean over more.”

“Well, there’s only one way to find out,” her father said. “Start scraping!”

What do you think will happen? Try the experiment yourself!

The two started scraping at the base of their rice piles. But as soon as they would start to build up a small cliff, the bottom would slide out and a small cascade of rice would flow down, turning the vertical wall into a horizontal slope. After a few minutes of diligent scraping, Peter tossed down his toothpick in disgust.

“I give up!” he declared. “The rice won’t make a cliff! It is even worse than what we saw on TV!”

“Peter’s right,” Mary agreed. “You can’t make a tall cliff out of rice.”

“You are both right,” her father said. “You can’t make a tall cliff out of rice and you can’t make a skyscraper out of sand. And in both cases, the reason is the same.”

“It is?” Mary asked.

“Yes,” her father replied. “What is happening is that every stack of stuff is a balance of two things. There is gravity, which is pushing down on all the parts of it and there is cohesiveness which is trying to keep everything together. When gravity pushed on the center of a pile of rice or a cliff or a skyscraper, the force is straight down. That creates pressure on the grains of rice which gets bigger as you go deeper into the pile. The rice on top feels very little pressure while the rice at the bottom feels a lot. If the pressure on a grain of rice is about the same as the pressure on the grains around it, everything is stable and nothing moves. But if the pressure is lower on one side, then things naturally try to move in that direction. And when the difference in pressure is greater than the cohesiveness, then -”

“You get a landslide!” Mary exclaimed.

“That’s right!” her father agreed. “If you watched carefully during your experiment, then you probably saw that the rice-slides only happened on the side where you were scraping. That was because that was the only side where the pressure was changing.”

“Oh!” Peter said with a look of sudden understanding. “And that’s why the cliffs were falling. When the water eroded enough of the base, the pressure from the dirt piled up in the cliff was more than the strength of the stuff holding the cliff together and – pow! – we got a landslide!”

“That’s right. And that should also tell you why you can’t build a twenty story cliff of rice or a two hundred story cliff of sand,” Mary’s father said.

“Because rice isn’t as strong as sand and that’s not as strong as the steel in a skyscraper!” Mary said. “But why could Peter’s mother have told us this, too?”

“Because she works with planets,” her father replied. “And the one part of the definition of a planet that everyone agrees on is that they are round thanks to their own gravity.”

“I don’t get it,” Peter said.

“Imagine that you are building a cliff of sand,” Mary’s father said. “What happens if it gets too tall?”

“Some of it collapses,” Peter said.

“OK, now imagine that you’ve got a pile of sand as big as a planet,” Mary’s father said. “What happens to that cliff?”

“It will collapse,” Mary said.

“And if the cliffs that creates are too tall?”

“Then they will collapse too,” Peter said.

“And what happens if you keep doing that all around the planet-sized sand pile?” Mary father asked.

“I get it!” Mary said. “No matter where you look, the sand piles can only be so tall. And that means that everywhere you look, everything is about the same distance from the center of the planet. And that makes it -”

“Round!” Peter and Mary chorused together.

“That’s right,” Mary’s father said. “And now, if you two will clean up your budding planets and if Peter will call his mother, we can eat dinner.”

With that reminder, Peter’s stomach once more rumbled threateningly and all three laughed as they set the table for dinner.

 

August 26 – Diamond Bright

Today’s factismal: It was once thought that things burned by releasing phlogiston.

If I were to ask you what water is made up of, odds are you’d tell me “H2O”. But did you ever stop to wonder how we know that? The answer is “Thanks to Antoine Lavoisier, who would be 270 years old today”. Known as “the father of modern chemistry”, Antoine had a quick mind and an inquisitive spirit that was willing to do things that no-one else dared. When he was born, the standard explanation for why things burn was that there was a “spirit” in them known as phlogiston that was generated heat and light as it was released; what was left over was known as calx. But Antoine wasn’t satisfied with that explanation. Why should metal gain weight when they lost phlogiston?

Antoine Lavoisier, the father of modern chemistry (Image courtesy Library of Congress)

Antoine Lavoisier, the father of modern chemistry
(Image courtesy Library of Congress)

Using a set of closed flasks, Antoine was able to show that gasses such as oxygen and nitrogen had different weights; before his work, everyone had thought that they were weightless or had the same weight. Even better, he was able to show that combining the different elements created new materials that had weights which could be found from the amount of each that was used. By changing chemistry from a purely qualitative science (“this plus this gives that”) to a quantitative one (” two parts hydrogen plus one part oxygen gives one part water”), he started chemists on the road to controlling the reactions and creating materials such as plastics, fertilizers, and light-weight alloys.

One of Antoine’s most famous experiments was also one of his most audacious. He wanted to prove that diamonds were made up of nothing but carbon. So he placed a large diamond into a flask and filled the flask with oxygen before sealing it. He then used a magnifying glass to set fire to the diamond. (Don’t try this at home!) After the diamond had finished burning, he was able to show that the resulting gas was the same that was produced when carbon was burned.

Sadly, Antoine’s contributions to science made him both famous and infamous. Because he lived in France during the time of the Revolution and because he came from an aristocratic family, he was soon tried on trumped-up charges and executed. Though the state formally pardoned him a year later, it nevertheless put an end to a career that changed the world.

If you’d like to honor Antoine’s memory, then why not go do a chemistry experiment today? The ACS has a website chock-full of stinky, smelly, chemistry fun:
http://www.acs.org/content/acs/en/education/whatischemistry/adventures-in-chemistry.html

June 20 – Disco Volante

Today’s Factismal: Ocean water has gotten 40% cloudier since 1950.

One way or another, we all depend on the ocean. It feeds us with fish, provides us with water thanks to storms, and transports heat from the equator to the  poles using currents and really, really big storms. But most importantly, the ocean takes up nearly a third of the carbon dioxide that is created on Earth. (The ocean puts out lots of CO2, but it takes in even more so that it is a net sink.)

When the ocean takes in CO2, it helps to keep the world cool.

When the ocean takes in CO2, it helps to keep the world cool.

The ocean removes CO2 from the air by two main methods. First, it just soaks in the CO2 much as  a sponge soaks in water and for much the same reason; there’s so much of it outside that some gets pushed inside. (In science-speak, that’s “the partial pressure of CO2 gas is higher in the atmosphere than it is in the ocean”.) When CO2 is absorbed by the oceans, it forms carbonic acid which is a weak acid that nonetheless can interact with a wide variety of things, including the calcium carbonate shells of coral and the mortar and cement holding bridges and piers together.

Bleached coral (My camera)

Bleached coral
(My camera)

The second way that the oceans remove CO2 is by the action of the critters that live in it. Tiny little bugs known as phytoplankton suck in the CO2 and use it during photosynthesis to make sugars and more phytoplankton; about half of all photosynthesis on Earth happens in the upper ocean waters. And those phytoplankton form the base of a food web that feeds little fish which feed bigger fish which feed huge fish which feed us. No phytoplankton means no fish tacos, sandwiches, and no soylent green! But those bugs need more than CO2 to grow; they also need light. And that’s where things aren’t looking too bright.

For reasons that are still unclear, the ocean waters have gotten cloudier over the past half century. That means that there is more debris and crud in the water, which means that less light makes it through to the phytoplankton. As a result, the phytoplankton can’t grow as quickly, which means that they absorb less CO2 and that there are fewer of them. That 40% decrease in light in the oceans has meant a 40% decrease in the plankton which has meant a decrease in both the amount of CO2 taken up and the number of fish that grow up.

Citizen scientists measuring the cocan's cloudiness with a Secchi disc (My camera)

Citizen scientists measuring the cocan’s cloudiness with a Secchi disc
(My camera)

But the most interesting thing about this is how we know that the oceans have gotten 40% cloudier. We know it thanks to citizen scientists like you. Citizen scientists have been using a flat black and white plate known as a Secchi disc to measure the visibility in the water. By taking measurements on boats and in streams and lakes, these citizen scientists have provided invaluable ground truth for scientists around the world! If you’d like to take part, then download the Secchi app and start measuring!
http://www1.plymouth.ac.uk/marine/secchidisk/Pages/default.aspx

December 17 – Going slow

Today’s fasctismal: The oldest age that carbon-14 can give is 114,600 years; the youngest is 570 years.

If you have ever cleaned up a teenager’s room, then you have probably discovered one of the most fundamental tools of archeology: relative dating. (You’ve also discovered what it feels like to excavate a midden pile.) As you dug down through the layers of trash, petrified food, and old homework assignments, you probably noticed that the older stuff was on the bottom and the newer stuff was on the top. But what might surprise you more than the Wall Street Journal hidden under your child’s bed is the fact that until 1949, relative dating was about the only method that archeologists had for dating really old artifacts.

That’s because very few artifacts come with a date on them. And even those that do come with an identifying mark, such as coins, only give you an approximate range of dates; for example, a coin with Julius Caesar’s face on it was probably minted sometime between 50 BCE (when he conquered Gaul) and 44 BCE (when .his political opponents put a permanent end to his ambitions). And the older something is, the less likely it is to have any sort of identifying mark; an empty, twelve hundred year old clam shell from the Spiro Mound looks an awful lot like an empty, fifteen thousand year old clam shell from Siberia.

This coin provides an approximate date (Image courtesy Australian Centre for Ancient Numismatic Studies)

This coin provides an approximate date
(Image courtesy Australian Centre for Ancient Numismatic Studies)

Archeologists have come up with several methods for working around this problem (e.g., by counting tree rings), but they fail more often than not (after all, how many tree rings are there in a clay pot?). They needed something more. They needed a method that would work on almost everything and that could be easily verified. And, in 1949, a chemist by the name of Willard Libby gave it to them. He realized that by comparing the amount of carbon-14 that was in an object to the amount of carbon-12, he could tell how old something was. But, because carbon-14 had a half-life of 5,730 years, it could only be used to measure things that were between 0.1 and 20 half lives; that is, things that were no younger than 570 years old and no older than 114,600 years old.

But how does carbon dating work? In lieu of my usual citizen science link, tonight I’ll give you an experiment that you can do at home to understand this basic concept (Teachers: This works really well in a large class if you ad up everyone’s numbers.). To do the experiment, you’ll need 84 pennies, 16 nickles, and 16 dimes. We’ll pretend that the pennies are atoms of carbon-12; because carbon-12 is stable, it doesn’t decay. A carbon-12 atom today will still be a carbon-12 atom 100,000 years from now. And we’ll pretend that the dimes are carbon-14 atoms. Carbon-14 is unstable; in 5,730 years, half of the carbon-14 that is present today will decay into nitrogen-14. (We never run out of carbon-14 because it is always being created by cosmic rays hitting nitrogen-14 in the atmosphere and turning it into carbon-14.)

When a critter dies, the ratio of carbon14 to carbon-12 is fixed

When a critter dies, the ratio of carbon14 to carbon-12 is fixed

Now a living thing will take in carbon-12 and carbon-14, so the proportion of the two atoms will be roughly the same as is in the atmosphere. But once it dies, it stops adding new carbon. As a result, when the carbon-14 decays it changes the ratio of the carbon atoms. To see that, we need to do our experiment. Start by placing the pennies in a pile and lining up the dimes, all heads up. (If you want, you can draw a dead critter around the money.) This is what the ratio of carbon-14 to carbon-12 looked like right after the critter died. There were 84 pennies/carbon-12 atoms and 16 dimes/carbon-14 atoms. (This was a very small critter.)

After one half-life about half of the carbon-14 has turned into nitrogen-14

After one half-life about half of the carbon-14 has turned into nitrogen-14

Since we don’t want to wait 5,730 years for the atoms to decay naturally, we’ll flip the dimes, one by one. If the dime comes up heads, put it back in the critter because it didn’t decay. But if it comes tails, the carbon-14 atom decayed and turned into nitrogen-14 (aka, a nickle). You’ll probably have about eight of the dimes decay, so your new ratio will be 86 pennies/carbon-12 atoms to 8 dimes/carbon-14 atoms. Now flip the dimes again, once more replacing those that come up tails with nickles. Odds are that you’ll lose about 4 dimes this time and your ratio will be 86 pennies/carbon-12 atoms to 4 dimes/carbon-14 atoms. Do it again and you’ll get something close to 86 pennies/carbon-12 atoms to 2 dimes/carbon-14 atoms.

After two half-lives half of the remaining carbon-14 has turned into nitrogen-14

After two half-lives half of the remaining carbon-14 has turned into nitrogen-14

As you can see from the experiment, the ratio can tell you when a critter, such as a possum or a palm tree, died. And if that critter was then used to make something else, such as a shoe or a house, then we know about when the something else was made. So all you have to do to find out how old something is is measure the ratio of the carbon-14 to the carbon-12 in it. Pretty nifty, huh?

After three half-lives half of the remaining carbon-14 has again turned into nitrogen-14

After three half-lives half of the remaining carbon-14 has again turned into nitrogen-14

But I’m willing to bet that your ratios didn’t exactly match mine. That’s because we only used a very few atoms; in most living things, there are quadrillions of carbon atoms instead of just 100. But there are still some variances in the ratios because radioactive decay happens randomly. As a result, most carbon-14 ages have an error of about 3-5% (i.e., a 570-year old sample is probably somewhere between 540 and 600 years old).

So that’s our experiment on carbon dating. I hope you enjoyed it; I’ll be doing more things like this in the new year. And if you didn’t like it, remember that at least it was better than cleaning your room…