Carbon Dating HW

Name: Anthony Rios Could we be part Neanderthal? Directions: Read the explanation below about how carbon dating works and the situation provided. Words or phrases in bold and italics are ones that you should know. Complete the five problems listed below and submit this worksheet on D2L. Neanderthals were a primitive hominid species ( Homo neanderthalensis ) living in Europe approximately 350,000 years ago. Researchers believed that Neanderthals may have coexisted (maybe even interbred) with early Homo sapiens in parts of Eurasia. In order to accurately determine the extent of this overlap, they needed to pinpoint the latest date that Neanderthals still lived in the area. To do this, they used “ Carbon Dating ” of the rocks surrounding the neanderthal fossils. If the neanderthal population was still present when early humans arrived, then this supports the hypothesis that they may have mixed genetics. Carbon dating is used to identify the age of rocks or fossils. Here you will use a carbon decay standard curve to determine the age of a neanderthal fossil. A standard curve is a graph used to determine the amount of a substance at various timepoints. For example, the x-axis on our graph shows the number of half-lives that have passed since the sample was at 100%. The curve lists half-lives instead of years, because you can use this standard curve to estimate amounts for ANY radioactive substance, not just carbon. Different radioactive substances have different half-lives. For carbon, one half life is 5730 years. So after 5730 years, half of the carbon will have decayed. Based on this information we can determine if or for how long Neanderthals and early humans co-existed. Carbon 14 is a radioactive isotope . This means that it contains 2 extra neutrons . Carbon 12 is the most abundant form of the element on earth and the most stable. Its nucleus contains 6 protons and 6 neutrons. These extra neutrons make the atom unstable and they will “decay” over time and become new protons. Because the properties of an element are largely determined by the number of protons, this decayed atom becomes Nitrogen 14 . C 14 and C 12 exist in the atmosphere at very specific proportions, and this does not change.

While you are alive, you are taking in the same proportions of C 14 and C 12 that exist in the atmosphere and that C 14 continues to decay into N 14 but there is always a new amount of C 14 from the atmosphere to take its place. This means that the amount of C 14 and C 12 found in your system are ALWAYS at the same proportion as they are in the atmosphere. Until you stop breathing in and eating new carbon, when you are no longer alive. Then there is no NEW addition of C 14 , and over time all of the remaining C 14 will decay into N 14 . We know how long it takes C 14 to decay into N 14 , called its “half-life” and can therefore measure the ratio of C 14 to C 12 to identify how long that fossil has been decaying, how old it is. This is known as carbon dating. The following graph is called a standard curve. This shows the fractional amount of C 14 you would expect to find in a fossil after 1, 2, 3 etc half-lives. A half-life is the amount of time it takes for HALF of a radioactive substance to decay. For C 14 that time is 5730 years. That means if you have 5g of C 14 , you would find 2.5g of C 14 after 5730 years, and 1.25g after another 5730 years. Every 5730 years, the amount of C 14 is reduced by half, until there is only one atom left, and it decays leaving no remaining C 14 . How long that takes, depends on how much C 14 you started with. Because the ratio of C 12 to C 14 in the environment remains constant, we can measure the amount of C 12 in a fossil sample and calculate what the amount of C 14 would have been at the time the organism died. If we know how much C 14 we started with, then we can estimate the number of half-lives passed to result in the amount of C 14 that we currently measure. Problem 1: For each of the half-lives listed in the table, please write the corresponding fraction of C 14 that you would expect to be left.

Problem 3: The researchers have evidence that homo sapiens first arrived in the area approximately 42,000 years ago. Based on your calculations, did homo sapiens and homo neanderthalis potentially co-habitate? Yes, based on my calculations homo sapiens and homo neanderthalis did potentially cohabitate. Problem 4: Carbon dating works for fossils that are up to about 75,000 years old. Beyond that, there is too little C 14 remaining for it to be accurately detected. Most dinosaurs however went extinct 65.5 million years ago. Can carbon dating be used to age dinosaur fossils? Why or why not? Carbon dating cannot be used to establish the age of a dinosaur fossil. Carbon-14 is only useful for fossils that are younger than 75,000 years. Any carbon-14 that the body may have absorbed into its tissues during its existence would have decayed too much by the time a dinosaur fossil was discovered to be usable as a method to ascertain its age. Problem 5: Different radioactive isotopes have different half-lives. For example, radioactive uranium-235 has a half-life of 704 million years. If this was incorporated into dinosaur bones, could it be used to accurately date the dinosaur fossils? Why or why not? Yes, after 65.5 million years only about one tenth of the 235U would have decayed, leaving plenty to measure in the fossils.