The Slides are to be shown at the front and then each item is shown in turn and the pupils use their graphs to calculate the age of each item from the percentage of carbon found in them. take longer than you think, but keeps them engaged and there're questions to be answered in their books also.Easily modified for different abilities, with my low ability I made all the percentages either 75%, 50% or 25% to make it much easier for them. The worksheets can be used in a number of ways, I used them in two ways, I laminated them both in the same pouch front to back for them to use as a mini whiteboard and write directly on them with a whiteboard pen then rub out the ink for reuse for different questions and classes and to use as group work.
The stable form of carbon is carbon 12 and the radioactive isotope carbon 14 decays over time into nitrogen 14 and other particles.
Carbon is naturally in all living organisms and is replenished in the tissues by eating other organisms or by breathing air that contains carbon.
At any particular time all living organisms have approximately the same ratio of carbon 12 to carbon 14 in their tissues.
Where t is the age of the fossil (or the date of death) and ln() is the natural logarithm function.
If the fossil has 35% of its carbon 14 still, then we can substitute values into our equation.