தஞ்சாவூர் புதையலைக் கண்டுபிடிக்க உதவும் MUMMY
9 Minutes
Carbon dating explained for students: learn how C-14 isotopes and half-life reveal the age of ancient living organisms. A Tamil science lesson.
- How cosmic rays turn nitrogen in the atmosphere into Carbon-14
- Demonstrating half-life decay with a coin-toss experiment
- Calculating the age of a mummy sample using its carbon ratio
What this lesson teaches
Carbon dating is a scientific method used to determine the age of ancient organic remains, such as wood, fossils, or mummies, by measuring the amount of radioactive Carbon-14 left inside them. Because living organisms absorb carbon from their surroundings throughout their lifetimes, calculating how much Carbon-14 has broken down after death reveals how long ago they died.
How Carbon-14 forms
Atoms are typically stable when they contain an equal number of protons and neutrons in their nucleus. High-energy cosmic rays traveling from distant galaxies strike gas atoms in Earth's atmosphere, releasing subatomic particles including neutrons. When a free neutron strikes a normal nitrogen atom with seven protons and seven neutrons, it knocks out one proton and joins the nucleus. This change creates Carbon-14, an unstable isotope with six protons and eight neutrons, which bonds with oxygen to form carbon dioxide that plants and animals absorb.
Understanding half-life
- Radioactive decay is a random process where an unstable isotope emits radiation to transform into a stable atom.
- A coin toss demonstrates this decay, where tossing coins and discarding those landing on tails halves the remaining number each time.
- Graphing the remaining coins over multiple tosses produces an exponential curve of one-half, one-fourth, and one-eighth.
- The time needed for exactly half of the radioactive atoms in a sample to decay is called its half-life.
- Carbon-14 has a half-life of 5,730 years, so half decays into nitrogen after 5,730 years and three-quarters decay after 11,460 years.
Measuring a sample's age
Living organisms continuously maintain the atmosphere's ratio of Carbon-12 to Carbon-14, which is roughly one trillion Carbon-12 atoms for every single Carbon-14 atom. When an organism dies, it stops breathing and eating, meaning fresh carbon intake halts while the trapped Carbon-14 slowly decays away. In a laboratory, scientists first wash away foreign contaminants through chemical processes and then ionize the sample's carbon atoms with extra electrons. An accelerator mass spectrometer then counts the exact ratio of Carbon-12 to Carbon-14 atoms, revealing the number of half-lives that have passed.