Tests looking for a variable decay probability by changing the pressure, temperature, and chemical combinations of the surrounding material have not found any variation in the decay probability. Yes, radioactive isotopes present in rocks and other ancient material decay atom by atom at a steady rate, much as clocks tick time away. Create a model of radioactive decay using dice and test its predictive power on dating the age of a hypothetical rock or artifact.
As humans, it seems easy for us to keep track of time lapses, as long as they range from a couple of seconds to a number of years.
Geologists (along with paleontologists, archeologists, and anthropologists) actually turn to the elements for answers to their geological time questions. While an element always has the same atomic number, meaning it has the same number of protons in its nucleus, it can have a different number of total nucleons in its nucleus.
Geologists who want to date objects are interested in the isotopes that change identity as they undergo radioactive decay. It is now time to explore why geologists are so interested in these radioactive decay processes as a means of dating objects.
Radioactive decay processes happen at a stable measurable rate characterized by the half-life time. The steady, atom-by-atom transformation of one isotope to another is not affected by any influence of the environment outside the nucleus. Proceeds from the affiliate programs help support Science Buddies, a 501( c ) 3 public charity. Collect data for a decay of 100 isotopes over time and record your results in the data table. Start by writing down "100" for the "Number of parent isotopes left" in your data table for Trial 1 (you will use 100 dice in your sample). Note this number in your data table under "Number of parent isotopes left" for the following time slot.
Place all the remaining dice (parent isotopes only) in your pot marked "Parent isotopes in sample" with the sticky note. Note that, at any given time during the process, the number of parent isotopes (dice in your pot) plus the number of daughter isotopes (dice in your bag) adds up to 100, which is the initial number of parent isotopes in the sample. Calculate the average of the number of parent isotopes left for each elapsed time and write it down in the "Average Value" column of your data table.
Calculate the fraction of parent isotopes remaining using the average numbers obtained in step 5 and write it down in the "Fraction of Parent Isotopes Remaining" column of your data table. For example, if your average value of parent isotopes left after one roll (time is 1) is 85, the fraction of parent isotopes left would be 85 divided by 100, or 0.85. In this part of the science project, you will create a graph of the decay curve of your isotope and use your curve to determine the half-life time of your isotope.
Having the collected data for your isotope decay organized in your data table, it is time to graph the decay curve.
The decay curve has the fraction of parent isotopes remaining in your sample represented on the y-axis. Create the graph by plotting all the data points and connecting them by a continuous line, as shown in Figure 4. Next you will calculate the half-life time of your particular isotope based on the probability that each isotope will decay within a unit of time passing.


Continue these calculations and fill out the data table in your lab notebook until no parent isotopes remain. It this section, you will ask a volunteer partner to roll the 100 six-sided dice, simulating the decay of isotopes in your sample just as you did to collect data for the decay curve. Once your partner stops, ask him or her to give the bag and pot back to you— but do NOT allow your partner to tell you how many times he or she rolled the dice at this point.
Count the number of parent isotopes remaining in the sample (number of dice in the pot) and write it down in your data table. Use your decay curve to estimate the number of times your partner rolled the dice (the elapsed time since formation of your sample) and write it down in your data table. Ask your partner to see his or her tallies, then count them and write them down in your data table.
Compare the last three columns (predicted time lapse based on your decay curve, predicted time lapse based on probability, and actual time lapse) of your data table. In this science project, you compare the half-life time read from the decay curve with the calculated half-life time. The Ask an Expert Forum is intended to be a place where students can go to find answers to science questions that they have been unable to find using other resources.
Just as a doctor uses tools and techniques, like X-rays and stethoscopes, to look inside the human body, geoscientists explore deep inside a much bigger patient—planet Earth. Everything in the environment, whether naturally occurring or of human design, is composed of chemicals. Statisticians use the power of math and probability theory to answer questions that affect the lives of millions of people.
The narrow range of ages is taken to be how long it took the parent bodies of the meteorites to form. Geologists use those radioactive isotopes to date volcanic ash or granite formations like the giant Half Dome in Yosemite National Park. In other words, they change their number of protons during radioactive decay and turn into a different element. The half-life time is the time period after which the remainder of the parent isotopes is half of what you start out with.
This means that half of the K-40 atoms existing today will have made the transformation to Ar-40 at some point during the next 1.25 billion years, no matter what weather they experience, pressure they undergo, or any other outside circumstances. The radioactivity levels are indicated by wiggly arrows; green dots represent parent isotopes (here, K-40) and yellow dots represent daughter isotopes present in the rock at the indicated time after the formation of the rock.
This figure also illustrates how to use a decay curve to figure the time since formation, if the fraction of parent isotope remaining in the sample is known. This geology science project will guide you through the process of radiometric dating, enabling you to explore and fill in the blanks. It's not as smart as you are, and it may occasionally give humorous, ridiculous, or even annoying results!
The model uses 100 six-sided dice, where each die represents one isotope in a radioactive sample used for dating.
Table showing how parts of the isotope decay model match up scientifically with the parts of radioactive isotope decay.
Determine the range of your x-axis based on the data in your data table, divide your x-axis in appropriate equal-length units so all the values fit on your axis, and add reference numbers and labels.


Determine the range of your y-axis based on the data in your data table, divide your axis in appropriate equal length units, and add reference numbers and labels.
In your lab notebook, make a data table like this one to calculate the number of parent isotopes remaining in a sample over time and determine the half-life time of your isotope based on probability.
In this variation, you do not change the sample size to graph the decay curve or make your probability data table, only the test sample involving a partner changes.
Geoscientists seek to better understand our planet, and to discover natural resources, like water, minerals, and petroleum oil, which are used in everything from shoes, fabrics, roads, roofs, and lotions to fertilizers, food packaging, ink, and CD's. They tell educators which teaching method works best, tell policy-makers what levels of pesticides are acceptable in fresh fruit, tell doctors which treatment works best, and tell builders which type of paint is the most durable. The atomic number is important for locating an element on the periodic table, shown in Figure 2. Radioactive refers to the characteristic that these isotopes are unstable and tend to fall apart.
As an example, the potassium-40 isotope (which contains 19 protons, 40 nucleons, and is represented by the atomic symbol K) will change into the argon-40 isotope (which contains 18 protons, 40 nucleons, and is represented by the symbol Ar). Science cannot predict which particular K-40 atom in this sample will decay and which will not during the next 1.25 billion years, but that is OK. The red lines show how to obtain the half-life time, or the time after which half of the parent isotopes have decayed. When trying to figure out how many rolls your partner has made, be sure to start with the number of parent isotopes that he or she decides to use in the sample size. Our Experts won't do the work for you, but they will make suggestions, offer guidance, and help you troubleshoot. They are employed in virtually every type of industry imaginable, from engineering, manufacturing, and medicine to animal science, food production, transportation, and education. When this happens, potassium-40, which is emitting particles in its conversion to a more stable form, is called the parent isotope. These are just some of the big and fascinating questions that anthropologists try to answer. It is like flipping a huge amount of coins: you know that the likelihood, or probability, is that you will end up with half of them heads up, but you have no idea which particular one will end up heads, or if even half of them will be heads for sure.
The arrows indicate how to read the graph, starting from a fraction of parent isotope remaining via a horizontal line to a point on the curve, and then vertically down to a time on the time axis. You will create a decay curve for your hypothetical rare isotope, and use it to estimate the time since formation of hypothetical samples created by a friend.
Anthropologists study all aspects of human life, in every region of the world, throughout all time. They might focus on everything from present-day cultures and human behavior, traditions, and prehistoric cultures to the biology and evolution of humans, or the origin and evolution of language.




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