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Introduction to exponential decay

Visit us (http://www.khanacademy.org/science/healthcare-and-medicine) for health and medicine content or (http://www.khanacademy.org/test-prep/mcat) for MCAT related content. These videos do not provide medical advice and are for informational purposes only. The videos are not intended to be a substitute for professional medical advice, diagnosis or treatment. Always seek the advice of a qualified health provider with any questions you may have regarding a medical condition. Never disregard professional medical advice or delay in seeking it because of something you have read or seen in any Khan Academy video. Created by Sal Khan.

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• If this is an MCAT channel, I'm not sure why problems that cannot solved without using a calculator are examples?
• What is the mathematical process of using Carbon-14 to calculate the age of very old objects?
• Good question, @Wudaifu! In order to use 14C dating, the sample/object in question must have at one point been alive, which is why this method is often used to date fossils. There is a known background level of 14C in the biosphere, which is caused by the conversion of nitrogen to 14C in the atmosphere as a result of cosmic radiation and which remains practically constant through the ages. While organisms are alive, they are continuously exchanging carbon with their environment, and therefore the concentration of 14C in their biomass is equal to the background concentration in the environment. After the organism dies, the 14C decays but is no longer replaced because there ceases any interaction between the organism and its surroundings.

Thus, if we were to date a sample, we would utilize the equation in the video, substituting the background 14C concentration (which would be equal to the original concentration in the sample) for Nₒ and the sample's concentration for N; lambda would be equal to the value given in the video. We would then solve the equation for "t" like Sal did starting at , which would give us the number of years that had elapsed since the organism died.