How Do Scientists Determine the Age of Ancient Bones?

Are you interested in the past? Even if history isn’t your favorite subject, you have probably been fascinated by historical events at some point, whether it’s the horrors of World War I or the sinking of the Titanic.

For events that have taken place in the last century or so, historians can often piece together detailed accounts of what happened using photographs and written records. However, as you go further back in time, it becomes more challenging to get a clear understanding of people and events.

Consider the difficulties that archaeologists and paleontologists face, for example. When they discover a dinosaur during an excavation in a remote area of the world, how do they reconstruct the history of the creature they have unearthed?

Will they find a diary or an old photo album? Unlikely! Instead, these scientists rely on careful observation and advanced scientific techniques to learn more about these ancient animals. One of the first things they often try to determine is the age of the creature using the fossilized bones they uncover.

But how can old bones provide scientists with information? One scientific method commonly used is carbon-14 dating. This technique has proven to be quite accurate in determining the age of ancient artifacts with a biological origin, such as bones, wood, or plant fibers, up to approximately 60,000 years old.

Carbon-14 is an isotope of regular carbon, also known as carbon-12. Isotopes are atoms of an element that have a different number of neutrons than the stable form of the element.

Carbon-14 is radioactive and occurs naturally in the atmosphere when cosmic rays collide with nitrogen atoms. When carbon-14 atoms combine with oxygen, they form carbon dioxide that is absorbed by plants. When humans and animals consume plants, they ingest carbon-14 atoms.

Carbon-14 atoms decay at a constant rate because they are radioactive. The rate at which a radioactive isotope decays is determined by its half-life, which is the time it takes for half of the atoms in the isotope to decay. Scientists have measured the half-life of carbon-14 atoms to be approximately 5,700 years. At the same time, new carbon-14 is constantly being produced in the environment, resulting in a relatively stable percentage of carbon-14 in all living plants and animals.

When an animal dies, it no longer takes in new carbon. However, the carbon-14 it contains continues to decay, while the amount of carbon-12 remains constant. By comparing the ratio of carbon-12 to carbon-14 in the ancient, fossilized bones of a creature, scientists can estimate its approximate age through testing and analysis.

Since the half-life of carbon-14 is about 5,700 years, carbon-14 dating can only be reliably used to date objects up to around 60,000 years old. However, you may have heard scientists discussing objects that they claim are millions or even billions of years old. How do they arrive at these estimates?

Carbon-14 is not the only radioactive isotope that scientists can measure and use to date artifacts. Other radioactive isotopes, such as potassium-40, uranium-235, uranium-238, thorium-232, and rubidium-87, have half-lives that extend from millions to billions of years.

Give it a go

Are you prepared to go on a journey through time? Find a companion, whether it’s a friend or a family member, to assist you in exploring the following enjoyable activities:

  • Are you confused by isotopes? How is it possible for them to be atoms of the same element while having different numbers of neutrons? To gain a better understanding of isotopes, take a look at the Isotopes of Pennies activity online. Share your newfound knowledge with a friend or family member.
  • Radiometric dating relies on knowing the precise rate at which radioactive isotopes decay over time. Go online to read and try out the Radioactive Decay: A Sweet Simulation of Half-Life activity. Take note of at least three new facts you learn about radioactive decay.
  • Do you have what it takes to use carbon dating to determine the age of a fossil? Unless you become a scientist, such as an archaeologist or a paleontologist, you may never find out. However, in the meantime, you can try out the exciting Frosty the Snowman Meets His Demise: An Analogy to Carbon Dating activity online. Have fun and make sure to ask a friend or family member for assistance!

Sources of Wonder



1. How do scientists determine the age of ancient bones?

Scientists use a variety of methods to determine the age of ancient bones. One common method is called radiocarbon dating, which measures the amount of carbon-14 in the bones. Carbon-14 is a radioactive isotope that decays over time, so by measuring the amount of carbon-14 remaining, scientists can estimate the age of the bones.

2. What other dating techniques do scientists use for ancient bones?

In addition to radiocarbon dating, scientists also use other dating techniques such as uranium-series dating and thermoluminescence dating. Uranium-series dating measures the decay of uranium isotopes in the bones, while thermoluminescence dating measures the amount of radiation that has been absorbed by the bones over time.

3. Can scientists determine the age of ancient bones accurately?

While scientists can determine the age of ancient bones with a reasonable degree of accuracy, there is always some margin of error. The accuracy of the dating methods depends on a variety of factors, including the preservation of the bones and the availability of suitable dating techniques.

4. How far back in time can scientists date ancient bones?

The dating methods used by scientists can generally determine the age of ancient bones up to around 50,000 years old. Beyond that, the amount of carbon-14 remaining in the bones becomes too small to accurately measure. For older bones, scientists may use other dating techniques, such as uranium-series dating, which can provide estimates up to several hundred thousand years.

5. Why is it important for scientists to know the age of ancient bones?

Knowing the age of ancient bones is important for a variety of reasons. It allows scientists to study the evolution and migration patterns of human ancestors, as well as the development of ancient civilizations. It also helps in understanding the environmental and climatic changes that occurred in the past. Additionally, dating ancient bones can provide insights into the origins and spread of diseases throughout history.

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