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Posts Tagged ‘radiometric dating’

Sorry Creationists, Radiometric Dating Still Works

September 21, 2010 2 comments

About a month ago, there was a story about scientists from Purdue University claiming that they have measured changes in decay rates of certain isotopes. The changes, they claimed, corresponded to the orbit of the Earth around the sun, and the rotation of the core of the sun.

They hypothesized that it could be neutrinos emitted from the sun’s core interacting with the radioactive substances, causing a change in their decay rate.

I’ve written a post previously on radiometric dating. The technique is used to estimate the age of archaeological samples and rocks. It is used to determine the age of skeletons, fossils, and rocks. The geologic history of the Earth is based on these techniques, and it is how we know how old the Earth is.

So any inconsistency with the decay rate of an isotope we use for these dating techniques would be interesting indeed. But, perhaps not surprisingly, I am skeptical.

One of the scientists was quoted as saying,

What we’re suggesting is that something that can’t interact with anything is changing something that can’t be changed.

Very aptly put. Neutrinos are particles emitted by the sun and very nearly massless. Billions of them pass through you every second and do not interact with the atoms and molecules in your body.

So the idea that they may, somehow, be able to change the decay rates of radioactive isotopes is quite an extraordinary claim, and it therefore requires extraordinary evidence.

This article states that

The Purdue team has ruled out the possibility of experimental error or an environmental influence on the detection systems.

That claim, any scientist will tell you, is at best bold, and at worst laughable. Being able to conclusively eliminate all environmental factors is very difficult indeed. Particularly in the work of these scientists, who used data and labs in several different locations.

That the orbit of the Earth could have any measurable effect on these isotopes is very unlikely. Consider this. Some have claimed that because the Earth’s orbit is elliptical,  the Earth is sometimes closer to the sun than at another part of the year. This could increase the flux of neutrinos and possibly account for changing decay rates of isotopes.

The Difference in Earth-Sun distance between aphelion and perihelion is about 4 million km (diagram is not to scale). Picture Credit: NASA

This seems unlikely, since the flux of neutrinos changes by only about 5% though the course of the year (I did that math myself, feel free to check it if you wish).

In addition, their study looked at decay rates of several different isotopes, and used data from a variety of labs. This is not a controlled experiment, but we can’t discount the findings simply because of that. However, they also found that the change of decay rate they measured was not the same for all of the isotopes they studied. So this could mean that the neutrinos are interacting differently with each isotope, or it could mean they are simply getting anomalous readings.

Other scientists are starting to respond as well. A study was recently published which measured the decay rate of Gold-198 over several weeks. The researchers set up the experiment so that one sample got many times more neutrinos bombarding it than the control sample. No detectable change in radioactive decay was measured.

So the question is still largely unsettled. Oh but wait. Even though Creationists and Young Earth Theorists love to take studies like this and spin them to say that the Earth may not be as old as we thought, consider this…

The changes the Purdue researchers measured were fractions of a percent. They would not have any significant effect on the dating of any geological or archaeological sample. So even if their numbers are right (which I don’t think they are) they wouldn’t affect our measurement of the age of the Earth.

But this is what science is all about. Making a discovery and then trying to prove it to the rest of the world. Whether the neutrino theory turns out to be true or not, it is a classic example of why science works.

The Physics of Carbon Dating

August 13, 2010 Leave a comment

When I was a kid, I wanted to be a hockey player. Then a doctor. Then a paleontologist. Then I saw Raiders of the Lost Ark and I wanted to be an archeaologist.

Well one thing led to another, and I ended up getting a Physics degree instead. Luckily for me though, studying physics gave me the tools and experience to understand all kinds of stuff from other scientific fields.

Take archeology and geology for example. One of the primary tools in this field for determining the age of a specimen is radio-carbon dating. But how does it work, and why do we place so much stock in its results?

Lets start at the beginning. Carbon is atomic element #6. The most abundant form of Carbon is Carbon-12, which has 6 protons and 6 neutrons in its nucleus (6 + 6 = Carbon-12).

We are Carbon-based life forms. Carbon has the ability to form huge molecules making our existence possible. (Silicon also has the ability to form big molecules, which Star Trek has taken advantage of to create some crazy looking Silicon-based aliens).

But there is another form of Carbon out there: Carbon-14 (C14 for short), which has 6 protons and 8 neutrons.

C14 is unstable. That extra neutrons cause problems in the nucleus so eventually Carbon-14 will decay into the happy and stable Nitrogen-14 (which actually makes up 78% of the air we breathe).

So how does this help us with dating stuff? Well C14 is naturally created in the atmosphere. So at any given time, there is a certain amount of C14 in the atmosphere. So when plants undergo photosynthesis, which is when plants take in Carbon dioxide and sunlight to make energy, they absorb some C14 at the same time. After this happens, animals will eat these plants and absorb some C14  themselves.

From: HowStuffWorks.com

Long story short, all living things will have a certain amount of C14 in their systems while they are alive.

But when plants or animals die, they stop taking in C14 from the environment. And since C14 is unstable, it will start to decay.

C14 has a half-life of 5730 years. This means that one half of C14 in a sample will decay after one half-life. For example, if you had 10 grams C14 atoms and waited 5730 years, 5 grams will have decayed, and you would have 5 grams of C14 left. If you waited another 5730 years, 2.5 grams will have decayed and you would have 2.5 grams left, and so on.

So scientists can take a fossilized sample of bone or plant, compare the amount of C14 in the sample to what should be in living tissue, and they can calculate how old the sample must be.

Granted, this is a simplified explanation I have given here, and there are other factors to consider. But calibration of the technique is very good, and we can get an accuracy of the age of a sample to with +/-16 years for a sample younger than 6000 years, and within 160 years for samples less than 50,000 years old.

After 50,000 years, C14 dating doesn’t work so well, because there just isn’t enough C14 to make an accurate measurement. But there are other elements with long half-lives that we can use to date much older stuff, and they all work on the same general principle as what I’ve explained here.

Many Intelligent Design proponents and Young Earth theorists will try and disprove these techniques. They may give arguments about how concentration of C14 has not been constant over the past 50,000 years. This is actually true, but we can account for it in our measurement.

So sorry IDers, the Earth was not created 6000 years ago. It was created roughly 4.5 billion years ago which, I think, is much more awesome.