Chapter 8: Fossils and Their Place in Time and Nature | Our Origins, 2e: W. W. Norton StudySpace
Unit 2 Lesson 3 Absolute Dating How can the absolute age of rock be determined? Radioactive isotopes 8 What are some radiometric dating methods? Unit 2. Fossil. Geologists. Half-life. Relative age dating. HELPFUL TERMS . What to do : 1. 2. 3. 4. 5. 6. 7. 8. 9. Your Team's Results. Other Team's Results. How many. Radiometric dating uses radioactive decay of minerals in rocks and fossils to Answer: 1/(23) = 1/8; What is the percentage of parent material remaining after 5 .
Determining the actual age of an event or object in years is called absolute dating. Scientists often use radioactive isotopes to find the absolute age of rocks and other materials. Atoms of the same element that have a different number of neutrons are called isotopes. Unit 2 Lesson 3 Absolute Dating How can the absolute age of rock be determined?
Radioactive isotopes are isotopes that are unstable and break down into other isotopes by a process called radioactive decay. The radioactive isotope is called the parent isotope, and the stable isotope formed by its breakdown is called the daughter isotope.
Half-life is the time needed for half of a sample of a radioactive element to undergo radioactive decay and form daughter isotopes. After one half-life has passed, one-half of the parent isotope has changed into daughter isotopes.
Scientists study the amounts of parent and daughter isotopes to date samples.
Unit 2 Lesson 3 Absolute Dating - ppt download
Finding the absolute age of a sample by determining the relative percentages of a radioactive parent isotope and a stable daughter isotope is called radiometric dating.
Unit 2 Lesson 3 Absolute Dating What is the best rock for radiometric dating? Igneous rocks are the best types of rock samples to use for radiometric dating. When igneous rocks form, minerals in them often contain only a parent isotope and none of the daughter isotope.
This makes the isotope percentages easier to interpret and helps dating to be more accurate. Scientists use many different isotopes for radiometric dating. The type of isotope used depends on the type of material being dated.
The half-life of the isotope used is also very important. Unit 2 Lesson 3 Absolute Dating What are some radiometric dating methods? Radiocarbon dating is a method used for dating wood, bones, shells, and other organic remains. All living things have a constant ratio of radioactive carbon to carbon Once a plant or an animal dies, no more carbon is taken in.
The ratio between the isotopes changes because carbon undergoes radioactive decay. The half-life of carbon is 5, years. For example, U is an unstable isotope of uranium that has 92 protons and neutrons in the nucl eus of each atom.
Through a series of changes within the nucleus, it emits several particles, ending up with 82 protons and neutrons. This is a stable condition, and there are no more changes in the atomic nucleus.
A nucleus with that number of protons is called lead chemical symbol Pb. The protons 82 and neutrons total This particular form isotope of lead is called Pb U is the parent isotope of Pb, which is the daughter isotope.
Many rocks contain small amounts of unstable isotopes and the daughter isotopes into which they decay. Where the amounts of parent and daughter isotopes can be accurately measured, the ratio can be used to determine how old the rock is, as shown in the following activities.
That chance of decay is very small, but it is always present and it never changes. In other words, the nuclei do not "wear out" or get "tired". If the nucleus has not yet decayed, there is always that same, slight chance that it will change in the near future. Atomic nuclei are held together by an attraction between the large nuclear particles protons and neutrons that is known as the "strong nuclear force", which must exceed the electrostatic repulsion between the protons within the nucleus.
In general, with the exception of the single proton that constitutes the nucleus of the most abundant isotope of hydrogen, the number of neutrons must at least equal the number of protons in an atomic nucleus, because electrostatic repulsion prohibits denser packing of protons.
But if there are too many neutrons, the nucleus is potentially unstable and decay may be triggered. This happens at any time when addition of the fleeting "weak nuclear force" to the ever-present electrostatic repulsion exceeds the binding energy required to hold the nucleus together.
- Unit 2 Lesson 3 Absolute Dating
In other words, during million years, half the U atoms that existed at the beginning of that time will decay to Pb This is known as the half life of U- Many elements have some isotopes that are unstable, essentially because they have too many neutrons to be balanced by the number of protons in the nucleus. Each of these unstable isotopes has its own characteristic half life.
Fossils and Their Place in Time and Nature
Some half lives are several billion years long, and others are as short as a ten-thousandth of a second. On a piece of notebook paper, each piece should be placed with the printed M facing down.
This represents the parent isotope. The candy should be poured into a container large enough for them to bounce around freely, it should be shaken thoroughly, then poured back onto the paper so that it is spread out instead of making a pile. This first time of shaking represents one half life, and all those pieces of candy that have the printed M facing up represent a change to the daughter isotope.
Then, count the number of pieces of candy left with the M facing down. These are the parent isotope that did not change during the first half life. The teacher should have each team report how many pieces of parent isotope remain, and the first row of the decay table Figure 2 should be filled in and the average number calculated. The same procedure of shaking, counting the "survivors", and filling in the next row on the decay table should be done seven or eight more times.
Each time represents a half life. Each team should plot on a graph Figure 3 the number of pieces of candy remaining after each of their "shakes" and connect each successive point on the graph with a light line.
AND, on the same graph, each group should plot points where, after each "shake" the starting number is divided by exactly two and connect these points by a differently colored line.
After the graphs are plotted, the teacher should guide the class into thinking about: Is it the single group's results, or is it the line based on the class average? U is found in most igneous rocks. Unless the rock is heated to a very high temperature, both the U and its daughter Pb remain in the rock. A geologist can compare the proportion of U atoms to Pb produced from it and determine the age of the rock.
The next part of this exercise shows how this is done. Each team is given a piece of paper marked TIME, on which is written either 2, 4, 6, 8, or 10 minutes.