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Over the timescale of human history, maybe someone turns to their library to study the histories that have been written. From that, they can piece together how long ago something happened. But things are not always that easy. What if something happened before writing was invented?

What if a skull is discovered in a backyard while someone is digging a trench? How do they know whether it is a person who ran afoul of Don Corleone or a grave of archaeological significance? There are a number of ways, mostly looking at indirect clues. However, there is one method that works extremely well for biological samples, which is to say things that were once alive.

This method is called carbon dating. Every living thing is made of carbon, along with other elements. Carbon is a great element from which to make life. The reason is that carbon can make lots of connections, what scientists call bonds, to other atoms. Because of this, organic chemistry, which is the chemistry involving the element carbon, is far more complex than other forms of chemistry. At an atomic level, though, one does not need to know any of that.

One just needs to know that humans, and every living thing, have a lot of carbon. In fact, if the human body is broken down into its constituent elements, carbon is the second most prevalent in terms of mass. Oxygen makes up more, but that is because oxygen is found in water, and H2O or water is a big component of blood and tissues. This is a transcript from the video series Understanding the Misconceptions of Science. Watch it now, on The Great Courses Plus. It might surprise people to learn that there are several different kinds of carbon.

Carbon is an element that contains six protons at the center of the atom. And that is always true. An atom with six protons is carbon. The most common kind of carbon also contains six neutrons and is called carbon The 12 comes from the number of protons and neutrons because six plus six equals But not all forms of carbon contain just six neutrons. There is carbon 13, which consists of six protons and seven neutrons. And there is also carbon 14, which consists of six protons and eight neutrons.

From a chemical point of view, there is no substantive difference between carbon 12, carbon 13, and carbon But, from a nuclear physics point of view, these different versions of carbon are what scientists call isotopes. Carbon 12 and carbon 13 are stable and exist forever. However, carbon 14 is slightly radioactive and decays. Learn more about exposing the truth about radiation. Carbon 14 decays into nitrogen 14 by beta decay.

This means that a neutron in a carbon 14 atom turns into a proton and an electron, and the electron escapes. If that decayed electron is seen, it is possible to know that a carbon 14 atom has decayed. The half-life of carbon 14 is approximately 5, years. Remember that half-life is the amount of time it takes for half of the substance to decay into the daughter product. In two half-lives, what will remain is a quarter of the original substance because half of a half is a quarter, and so on.

This process of carbon 14 decay, which starts after the death of a living thing, can be thus utilized to determine the age of the dead organic matter. Carbon 14 dating changed the world of archaeology. Dating objects became relatively easy, although doing it precisely takes some care. Libby reached out to Aristid von Grosse — of the Houdry Process Corporation who was able to provide a methane sample that had been enriched in carbon and which could be detected by existing tools.

Using this sample and an ordinary Geiger counter, Libby and Anderson established the existence of naturally occurring carbon, matching the concentration predicted by Korff. This method worked, but it was slow and costly.

They surrounded the sample chamber with a system of Geiger counters that were calibrated to detect and eliminate the background radiation that exists throughout the environment. Finally, Libby had a method to put his concept into practice. The concept of radiocarbon dating relied on the ready assumption that once an organism died, it would be cut off from the carbon cycle, thus creating a time-capsule with a steadily diminishing carbon count.

Living organisms from today would have the same amount of carbon as the atmosphere, whereas extremely ancient sources that were once alive, such as coal beds or petroleum, would have none left. For organic objects of intermediate ages—between a few centuries and several millennia—an age could be estimated by measuring the amount of carbon present in the sample and comparing this against the known half-life of carbon Among the first objects tested were samples of redwood and fir trees, the age of which were known by counting their annual growth rings.

Relative dating simply places events in order without a precise numerical measure. By contrast, radiocarbon dating provided the first objective dating method—the ability to attach approximate numerical dates to organic remains. This method helped to disprove several previously held beliefs, including the notion that civilization originated in Europe and diffused throughout the world.

By dating man-made artifacts from Europe, the Americas, Asia, Africa and Oceania, archaeologists established that civilizations developed in many independent sites across the world. As they spent less time trying to determine artifact ages, archaeologists were able to ask more searching questions about the evolution of human behavior in prehistoric times. By using wood samples from trees once buried under glacial ice, Libby proved that the last ice sheet in northern North America receded 10, to 12, years ago, not 25, years as geologists had previously estimated.

When Libby first presented radiocarbon dating to the public, he humbly estimated that the method may have been able to measure ages up to 20, years. With subsequent advances in the technology of carbon detection, the method can now reliably date materials as old as 50, years. Seldom has a single discovery in chemistry had such an impact on the thinking in so many fields of human endeavor.

Seldom has a single discovery generated such wide public interest. It was here that he developed his theory and method of radiocarbon dating, for which he was awarded the Nobel Prize in Chemistry in Libby left Chicago in upon his appointment as a commissioner of the U.

Atomic Energy Commission. In , Libby returned to teaching at the University of California, Los Angeles, where he remained until his retirement in Libby died in at the age of The commemorative plaque reads:. In , Willard Libby — developed a method for dating organic materials by measuring their content of carbon, a radioactive isotope of carbon.

The method is now used routinely throughout archaeology, geology and other sciences to determine the age of ancient carbon-based objects that originated from living organisms. For this discovery, Libby received the Nobel Prize in Chemistry in Discovery of Radiocarbon Dating. Back to Landmarks Main Page. Learn more: About the Landmarks Program. If you do not respond, everything you entered on this page will be lost and you will have to login again. Careers Launch and grow your career with career services and resources.

Develop and grow in your career Find and land a job Explore career options Find networking opportunities Professional Communities Career Events. Communities Find a chemistry community of interest and connect on a local and global level. Discover Chemistry Explore the interesting world of science with articles, videos and more.

Awards Recognizing and celebrating excellence in chemistry and celebrate your achievements. Funding Funding to support the advancement of the chemical sciences through research projects. Dedicated at the University of Chicago on October 10, Libby Landmark dedication and acknowledgments Research resources. Willard F. Libby right , the physical chemist who conceived of radiocarbon dating, with graduate student Ernest Anderson. Willard Libby's concept of radiocarbon dating Willard Libby — , a professor of chemistry at the University of Chicago, began the research that led him to radiocarbon dating in Top of page.

The Keeling Curve The carbon cycle features prominently in the story of chemist Ralph Keeling, who discovered the steadily increasing carbon dioxide concentrations of the atmosphere.


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