Let’s go step by step to understand what’s happening in this diagram and how carbon-14 dating works.
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The whole process is about figuring out how old something made from living material (like wood, bone, or plant fibers) is — for example, an ancient spear.
Here’s how it works:
Step 1: Carbon in the atmosphere
- The air has two kinds of carbon atoms: regular carbon (called C-12) and a tiny bit of radioactive carbon (C-14).
- These are mixed evenly in the air all over Earth — whether you’re at sea level or up high, the ratio of C-14 to C-12 stays pretty much the same over time.
Step 2: Plants take in carbon
- Plants breathe in CO₂ from the air during photosynthesis.
- They don’t care which kind of carbon they get — so the ratio of C-14 to C-12 inside the plant matches the ratio in the air.
Step 3: Animals eat plants
- When animals (like rabbits) eat plants, they also take in that same mix of C-14 and C-12.
- So while alive, every living thing has the same C-14/C-12 ratio as the atmosphere.
Step 4: Death stops the intake
- Once a plant or animal dies, it stops taking in new carbon.
- But here’s the key: C-14 is radioactive and slowly breaks down (decays) over time. C-12 does not decay — it stays forever.
- So after death, the amount of C-14 goes down, but C-12 stays the same → the ratio changes.
Step 5: Measuring the change
- Scientists can measure how much C-14 is left in an old object (like a wooden spear).
- They compare it to how much C-14 would be in a living thing today.
- Since we know how fast C-14 decays (its half-life is about 5730 years), we can calculate how long ago the organism died.
Example from the image:
- A leaf (living tissue) shows a Geiger counter reading of
32.5 — that’s the “normal” activity level for living things.
- An old spear shows a reading of
13.6 — less radiation means less C-14 left → it’s older.
- By comparing 13.6 to 32.5, scientists figure out the age — in this case, around
5200 BC.
Modern method:
- Instead of Geiger counters, now they use machines called mass spectrometers that count actual C-14 and C-12 atoms directly — even more accurate!
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Final Answer:
Carbon-14 dating works because living things absorb carbon from the air with a fixed ratio of C-14 to C-12. After death, C-14 decays while C-12 stays constant. By measuring how much C-14 remains compared to C-12, scientists can calculate how long ago the organism died.
Parent Tip: Review the logic above to help your child master the concept of carbon dating worksheet.
