How Does Radiocarbon Dating Work? - Instant Egghead #28

Summary

The script from Scientific American Instant Egghead explains how scientists determine the age of fossils using carbon dating. It details the presence of two carbon isotopes, Carbon 12 and unstable Carbon 14, in living organisms. After an organism's death, Carbon 14 decays into nitrogen at a known rate, with a half-life of 5,730 years. By measuring the ratio of Carbon 14 to Carbon 12 remaining in a fossil, scientists can estimate its age up to approximately 60,000 years. For older specimens, elements with longer half-lives are used.

Takeaways

• 🕰️ Fossils contain an internal clock that helps determine their age.
• 🌳 For dating fossils, scientists use the ratio of Carbon-14 to Carbon-12 isotopes.
• 🌿 Plants absorb carbon from the atmosphere, including both Carbon-12 and Carbon-14.
• 🐘 Animals obtain carbon, including isotopes, by consuming plants.
• ⚛️ Carbon-12 has six protons and six neutrons, while Carbon-14 has six protons and eight neutrons.
• ☢️ Carbon-14 is radioactive and decays into nitrogen at a predictable rate.
• 📉 The half-life of Carbon-14 is 5,730 years, during which half of the Carbon-14 atoms decay.
• 🔍 By measuring the Carbon-14 to Carbon-12 ratio, scientists can estimate the time elapsed since an organism's death.
• 🦴 Carbon dating is effective for fossils up to approximately 60,000 years old.
• 🔬 For older fossils, scientists use other radioactive elements with longer half-lives for dating.

Q & A

How do scientists determine the age of fossils?

Scientists determine the age of fossils by measuring the ratio of Carbon 14 to Carbon 12 isotopes within the fossil.

What is the difference between Carbon 12 and Carbon 14?

Carbon 12 has six protons and six neutrons, while Carbon 14 has six protons and eight neutrons. Carbon 14 is unstable and decays over time.

How is Carbon 14 formed?

Carbon 14 is formed in the atmosphere when cosmic rays hit nitrogen atoms, causing a transformation into carbon with an unstable number of neutrons.

What is the half-life of Carbon 14?

The half-life of Carbon 14 is 5,730 years, which means that after this period, about half of the Carbon 14 atoms will have decayed into nitrogen.

How does the decay of Carbon 14 help in dating fossils?

The decay of Carbon 14 allows scientists to measure the time elapsed since the death of an organism by comparing the remaining Carbon 14 to the stable Carbon 12.

What is the maximum age limit for Carbon 14 dating?

Carbon 14 dating is effective for dating fossils up to approximately 60,000 years old.

Why can't Carbon 14 dating be used for very old fossils?

For very old fossils, the amount of Carbon 14 left is too small to measure accurately, so scientists use other dating methods with longer half-lives.

How do plants incorporate Carbon into their system?

Plants incorporate Carbon by taking in carbon dioxide from the atmosphere and using it to form complex organic molecules.

How do animals get their carbon?

Animals obtain carbon by consuming plants that have already incorporated carbon dioxide into their organic molecules.

What happens to the Carbon 12 in a fossil over time?

Unlike Carbon 14, the amount of Carbon 12 in a fossil remains constant over time and does not decay.

What alternative methods are used for dating fossils older than 60,000 years?

For dating older fossils, scientists use other unstable elements with longer half-lives, such as Potassium-Argon or Uranium-Lead dating.

Outlines

00:00

🕰️ Carbon Dating Explained

This paragraph explains the method of carbon dating, which is used to determine the age of fossils. Scientists use the ratio of two carbon isotopes, Carbon 12 and Carbon 14, to calculate the age. Carbon 14 is unstable and decays into nitrogen at a known rate, with a half-life of 5,730 years. By measuring the remaining Carbon 14 in a fossil, the time elapsed since the organism's death can be estimated. This method is effective for dating fossils up to approximately 60,000 years old. For older specimens, scientists rely on other radioactive isotopes with longer half-lives.

Keywords

💡Fossil

A fossil is the preserved remains or traces of animals, plants, and other organisms from the remote past. In the context of the video, fossils are crucial for understanding the age of ancient organisms. The script mentions that fossils have their own 'internal clock' which scientists can read to determine their age.

💡Carbon dating

Carbon dating, also known as radiocarbon dating, is a method used by scientists to determine the age of an organism by measuring the amount of carbon-14 remaining in its remains. The video explains that this method is effective for dating fossils up to about 60,000 years old, as it relies on the decay of carbon-14 into nitrogen.

💡Carbon-12 (C-12)

Carbon-12 is a stable isotope of carbon with six protons and six neutrons. It is the most abundant form of carbon found in nature. The script uses carbon-12 as a reference point in carbon dating, as its quantity in a fossil remains constant over time, unlike carbon-14.

💡Carbon-14 (C-14)

Carbon-14 is a radioactive isotope of carbon with six protons and eight neutrons. It is created in the atmosphere when cosmic rays hit nitrogen atoms. The video highlights that carbon-14 is unstable and decays over time, which is the basis for carbon dating.

💡Half-life

The half-life of a radioactive isotope is the time it takes for half of the atoms to decay. In the script, the half-life of carbon-14 is given as 5,730 years, which is used to calculate the age of fossils. After one half-life, an organism would have about half the amount of carbon-14 it started with.

💡Cosmic rays

Cosmic rays are high-energy particles originating from outer space that travel at nearly the speed of light. The video mentions that cosmic rays are responsible for creating carbon-14 in the atmosphere when they collide with nitrogen atoms.

💡Organic molecules

Organic molecules are compounds containing carbon, hydrogen, and often oxygen, nitrogen, and other elements. The script explains that plants use carbon dioxide from the atmosphere to form complex organic molecules, which are then incorporated into their structures and passed on to animals through the food chain.

💡Decay

In the context of the video, decay refers to the radioactive process where carbon-14 atoms break down into nitrogen. This decay is a key factor in carbon dating, as it allows scientists to measure the ratio of carbon-14 to carbon-12 in a fossil and estimate its age.

💡Ratio

The ratio of carbon-14 to carbon-12 in a fossil is a critical piece of data for carbon dating. The video explains that by measuring this ratio, scientists can determine how many thousands of years have passed since the animal died, as the amount of carbon-14 decreases over time.

💡Unstable elements

Unstable elements are those that undergo radioactive decay. The video notes that for dating fossils older than 60,000 years, scientists use other unstable elements with longer half-lives, indicating that different dating methods are employed depending on the age of the specimen.

Highlights

Fossils have an internal clock that can be read by scientists.

Carbon dating is used to determine the age of fossils by examining the ratio of two carbon isotopes.

All living things are made of carbon, which is obtained from plants or through the food chain.

Carbon 12 is the most common isotope with six protons and six neutrons.

Carbon 14 is created when cosmic rays hit nitrogen atoms in the atmosphere.

Carbon 14 is unstable and decays into nitrogen, which is a key factor in carbon dating.

The half-life of Carbon 14 is 5,730 years, during which half of the Carbon 14 decays.

After one half-life, an organism will have half the Carbon 14 it started with.

The ratio of Carbon 14 to Carbon 12 decreases over time, allowing scientists to measure age.

Carbon dating is effective for fossils up to approximately 60,000 years old.

For older fossils, scientists use other unstable elements with longer half-lives.

The method of carbon dating provides a way to measure the age of fossils by tracking carbon isotope decay.

Plants absorb Carbon 12 from the atmosphere to form organic molecules.

Animals obtain carbon, including Carbon 14, by consuming plants.

The decay of Carbon 14 in an organism's body can be tracked to determine its age since death.

The amount of Carbon 12 remains constant in an organism's body over time.

By measuring the Carbon 14 to Carbon 12 ratio, scientists can estimate the time elapsed since an animal's death.

For fossils older than 60,000 years, alternative dating methods using elements with longer half-lives are necessary.

Transcripts

Scientific American Instant Egghead

How do we know how old something is?

For people, we'd ask to see their birth certificate.

For trees, we'd count the rings.

But how do we know how old a fossil is?

Fossils have their own internal clock.

Scientists can read it by looking at the ratio of two different types of carbon atoms.

Of course, every living thing is made of carbon.

Plants grab carbon dioxide from the atmosphere

and use it to form complex organic molecules.

Animals get their carbon by eating these plants.

But there's more than one form of carbon.

Most carbon atoms have six protons and six neutrons.

We call this Carbon 12.

High up in the atmosphere, sometimes cosmic rays hit nitrogen atoms.

This creates carbon with six protons and eight neutrons.

We call this Carbon 14.

Carbon 12 and Carbon 14 behave alike.

But Carbon 14 has one unique and important attribute: it's unstable.

So once an animal dies, the Carbon 14 in its body will start to go away.

Every 5,730 years on average,

about half of the Carbon 14 atoms will decay into nitrogen.

This is its at half-life.

After one half-life, the animal will have

about half the amount of Carbon 14 it started with.

After another half-life, it will have about a quarter.

And after another half-life, it will have about an eighth.

By contrast, the amount of Carbon 12 it has in its body will stay the same.

By measuring the ratio of Carbon 14 to Carbon 12,

we can measure how many thousands of years have passed since the animal died.

Carbon dating works for fossils up to about 60,000 years old.

For older fossils, scientists use unstable elements that have much longer half-lives.

For Scientific American's Instant Egghead, I'm Michael Moyer.