What Is Carbon Dating and What Does It Tell Us?

Key Points

• Carbon dating is a method used by archaeologists to determine the age of ancient artifacts, up to 43,000-60,000 years old.
• Carbon-14, a radioactive isotope, is absorbed by living organisms and decays over time, allowing scientists to measure its ratio to carbon-12 to determine the age of once-living organisms.
• Carbon dating is accurate, but its limitations include only being able to date objects that were once alive and not being effective for inanimate objects like metals or plastic.

With the latest Indiana Jones movie release, citizen scientists have become fascinated with all things ancient. But how did the professor/ explorer know how old an object was? We’re not sure if Indie and his pals ever used carbon dating, but archaeologists regularly do.

Keep reading to learn what carbon dating is, what it tells us, and how it works. We’re diving into ancient artifacts, from mummies to pottery, to learn how archaeologists determine an object’s actual age, up to 43,000 – 60,000 years old, with carbon-14 dating.

First Things First: What Is Carbon-14, and How Is It Made?

Carbon-14 sounds complicated, and the formulas archaeologists use are complicated. But let’s break it down into the simplest terms possible: What is carbon dating, and what does it tell us?

• The Sun’s cosmic rays constantly penetrate Earth’s atmosphere. For example, you might get hit by a half million cosmic rays hourly since they continually enter the atmosphere.
• When cosmic radiation collides with an atom, it creates an energetic neutron (secondary cosmic ray).
• The neutron then collides with a nitrogen-14 atom and becomes a carbon-14 atom and a hydrogen atom.
  • Nitrogen-14 = seven neutrons and seven protons
  • Carbon-14 = eight neutrons and six protons
  • Hydrogen atom = zero neutrons and one proton
• Next, plants absorb the Sun’s energy in the form of carbon dioxide. And then, through photosynthesis, plants incorporate or take in the carbon-14 atoms created by the cosmic rays to create plant fibers and wood.
• Humans and animals eat plants and absorb carbon-14.
• After death and burial, beta decay affects bones and wood, causing them to lose carbon-14 and return to nitrogen-14.
• However, since carbon-14 comes from cosmic rays, it is radioactive and has a half-life of approximately 5,730 years.
• So, when scientists measure how much carbon-14 remains in a mummy or a wooden sarcophagus, they can tell how old it is. Or, more accurately, they can tell how long ago the organic object died.

Is Carbon-14 Found in Living Things?

Because plants absorb carbon dioxide, when people and animals eat plants, we take in carbon-14. The ratio of ordinary carbon (called carbon-12) to carbon-14 in the atmosphere and inside living beings remains nearly constant at any given time.

Something like 1 in a trillion carbon atoms are actually carbon-14. So, humans, and all living beings, contain carbon-14 at about the same ratio — one in a trillion. Interestingly, carbon-14 atoms continually decay but are replaced with new atoms constantly. So, the ratio balances out to stay the same.

The Low-Down on How Radiocarbon Dating Works

Scientists learn how long ago an organism lived and died by determining its remaining amount of carbon-14 relative to the remaining carbon-12. Here’s what carbon dating is and what it tells us.

When a living being dies, it quits taking in carbon. At the moment of death, the carbon-12 to carbon-14 ratio equals that of every other living organism. However, carbon-14 starts decaying without replacement, even while the carbon-12 amount stays the same.

Therefore, measuring the ratio of carbon-12 to carbon-14 (compared to a living sample) tells scientists a relatively precise age of the once-living organism.

Do Geologists Use Carbon Dating, and What Does It Tell Us About Rocks?

Earlier, you learned that carbon-14’s half-life is 5,730 years. And that means half the carbon-14 atoms decay into nitrogen-14 atoms after 5,730 years. Of course, after 11,460 years, only one-fourth of the carbon-14 atoms remain.

Since rocks are generally much older than tens of thousands of years, carbon dating does not work. So, geologists use other dating methods. For example, potassium-40 has a 1.26 billion-year half-life. Therefore, measuring how much potassium-40 decayed to argon gives geologists a much better way to date rocks.

However, if a geologist found an insect within a rock, carbon-14 dating may help determine when the insect lived and died.

Is Carbon Dating Accurate?

Carbon data is accurate. It’s a scientific method of determining the age of organic material samples. The sticking point for some scientists and laboratories is how far back the technique proves accurate.

Some labs say 43,000 years, while some universities say carbon dating tells us a sample’s age from up to 60,000 years ago.

Who Invented Carbon Dating?

Willard F. Libby was a physical chemistry professor at the University of Chicago when he and his team developed the carbon dating technique in 1949. He won a Nobel Prize in Chemistry for his work, which revolutionized how archaeologists and scientists interpret history.

Professor Libby had a storied career, even working with the Manhattan Project Team and Edward Condon to create a separation method (gaseous diffusion) for the uranium isotope that scientists used in the atomic bomb.

In addition, Libby’s work on natural tritium, or radioactive hydrogen, proved beneficial in hydrology (dating water) and geophysics.

Does Carbon-14 Have Limitations, and What Does It Tell Us?

The limitation of carbon-14 dating is that it can not be used on inanimate objects like metals or plastic. It can only tell us the age of an object that was once alive and the age of some inorganic materials.

And while that may initially seem limiting, organic objects actually include many items you might not immediately think of. Here are some common items that archaeologists use carbon-14 dating on, from the obvious to the not-so-obvious:

• People and animals (bones, mummies, hair, poop, nails, and blood)
• Plants
• Paper and cloth made from reeds or plant fibers
• Foods (grains and seeds)
• Animal hides and leather objects or clothing
• Logs from home or settlement-building
• Biofuels

How Has Carbon Dating Improved?

For many years, archaeologists used a mathematical formula to calculate the age of a given sample:

t = [ ln (Nf/No) / (-0.693) ] x t½

In = the natural logarithm

Nf/No = Percentage of carbon-14 compared to that in living tissue

T½ = Carbon-14’s half-life of 5,730 years

Today, automated machinery does much of the carbon dating work. For example, liquid scintillation counters (LSC) quantify a low-energy radioisotope’s radioactivity.

It uses surfactants (emulsifiers), scintillators (fluorescent), and organic solvents to absorb the radioisotope’s energy into detectable light pulses. Simply said, LSCs measure the radioactivity of beta-emitting isotopes like carbon-14.

Accelerator mass spectrometers (AMS) accelerate ions to high kinetic energies before analyzing the mass. For example, they can separate a rare isotope (like carbon-14) from a large mass (like carbon-12).

And in doing so, the mass spectrometer can detect radioisotopes with long half-lives. It quickens decay counting while also making it more precise. And AMS technology can work on tiny samples.

Is Carbon-14 Dangerous?

Carbon-14 is also called radiocarbon, and it is a faintly radioactive isotope. However, the radiation can barely penetrate a human’s outermost skin layer. And it doesn’t present a risk to animals or people, even with significant external exposures.

Wrapping Up: What Is Carbon Dating and What Does It Tell Us?

Carbon dating and what it tells us has made a significant impact on ancient discoveries. Some scientists might argue that understanding when an organism lived and died helps humans more fully recognize our history.

For example, archaeologists use radiocarbon dating to prove — and even disprove — theories. This way, they can better understand our world and what happened thousands of years ago.