This activity on determining age of rocks and fossils is intended for 8th or 9th grade 5) To use radiometric dating and the principles of determining relative age to . Using the same reasoning about proportions as in Part 2b above, students.

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- Calculating Half-Life - Chemistry LibreTexts
- Radiometric dating

What is Relative Dating? What is the Age of the Solar System?

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Absolute Time in Geology. What is Carbon Dating? Methods for Determining Past Climates. Introduction to Physical Geology: Intro to Natural Sciences. Middle School Earth Science: Weather and Climate Science: UExcel Weather and Climate: Guns, Germs, and Steel Study Guide. Holt McDougal Introduction to Geography: Radiometric dating is used to estimate the age of rocks and other objects based on the fixed decay rate of radioactive isotopes. Radiometric Dating The aging process in human beings is easy to see.

Radioactive Decay The methods work because radioactive elements are unstable, and they are always trying to move to a more stable state. Half-Life So, what exactly is this thing called a half-life? Uranium-Lead Dating There are different methods of radiometric dating that will vary due to the type of material that is being dated. Potassium-Argon and Rubidium-Strontium Dating Uranium is not the only isotope that can be used to date rocks; we do see additional methods of radiometric dating based on the decay of different isotopes.

Radiocarbon Dating So, we see there are a number of different methods for dating rocks and other non-living things, but what if our sample is organic in nature? Try it risk-free No obligation, cancel anytime. Want to learn more? Select a subject to preview related courses: Lesson Summary Let's review.

Learning Outcomes As a result of watching this video, you might be able to: Compare radiometric dating, radioactive decay and half-life Understand that uranium-lead dating is one of the most reliable radiometric dating methods Relate the processes of potassium-argon and rubidium-strontium dating Determine how radiocarbon dating works and recognize why it is important. Unlock Your Education See for yourself why 30 million people use Study.

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You are viewing lesson Lesson 6 in chapter 2 of the course:.

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Earth Science 24 chapters lessons 16 flashcard sets. Earth's Spheres and Internal Rock Deformation and Mountain Water Balance on Earth. Studying for Earth Science Online Textbook Help Holt Chemistry: Browse by Lessons What is Apert Syndrome? Latest Courses Computer Science Homeschool Curriculum The Great Depression Popular Lessons Fern Hill: Create an account to start this course today. Like this lesson Share. Browse Browse by subject. Upgrade to Premium to enroll in Earth Science Enrolling in a course lets you earn progress by passing quizzes and exams.

Take quizzes and exams. Earn certificates of completion. You will also be able to: Create a Goal Create custom courses Get your questions answered. Upgrade to Premium to add all these features to your account! When each team is ready with the pieces all showing "U", a timed two-minute interval should start. During that time each team turns over half of the U pieces so that they now show Pb This represents one "half-life" of U, which is the time for half the nuclei to change from the parent U to the daughter Pb A new two-minute interval begins.

Continue through a total of 4 to 5 timed intervals. That is, each team should stop according to their TIME paper at the end of the first timed interval 2 minutes , or at the end of the second timed interval 4 minutes , and so on. After all the timed intervals have occurred, teams should exchange places with one another as instructed by the teacher. The task now for each team is to determine how many timed intervals that is, how many half-lives the set of pieces they are looking at has experienced.

The half life of U is million years. Both the team that turned over a set of pieces and the second team that examined the set should determine how many million years are represented by the proportion of U and Pb present, compare notes, and haggle about any differences that they got. Right, each team must determine the number of millions of years represented by the set that they themselves turned over, PLUS the number of millions of years represented by the set that another team turned over.

Pb atoms in the pegmatite is 1: Using the same reasoning about proportions as in Part 2b above, students can determine how old the pegmatite and the granite are. They should write the ages of the pegmatite and granite beside the names of the rocks in the list below the block diagram Figure 1. This makes the curve more useful, because it is easier to plot it more accurately.

That is especially helpful for ratios of parent isotope to daughter isotope that represent less than one half life. For the block diagram Figure 1 , if a geochemical laboratory determines that the volcanic ash that is in the siltstone has a ratio of U If the ratio in the basalt is 7: Students should write the age of the volcanic ash beside the shale, siltstone and basalt on the list below the block diagram. Why can't you say exactly what the age of the rock is?

Why can you be more precise about the age of this rock than you could about the ages of the rock that has the trilobites and the rock that contains acritarchs and bacteria? Based on cross-cutting relationships, it was established that the pegmatite is younger than the slate and that the slate is younger than the granite. Therefore, the slate that contains the acritarch and bacteria is between million years and million years old, because the pegmatite is million years old and the granite is million years old.

The slate itself cannot be radiometrically dated, so can only be bracketed between the ages of the granite and the pegmatite.

## Calculating Half-Life - Chemistry LibreTexts

The trilobite-bearing limestone overlies the quartz sandstone, which cross-cuts the pegmatite, and the basalt cuts through the limestone. Therefore the trilobites and the rock that contains them must be younger than million years the age of the pegmatite and older than million years the age of the basalt. The limestone itself cannot be radiometrically dated, so can only be bracketed between the ages of the granite and the pegmatite.

The Triceratops dinosaur fossils are approximately 70 million years old, because they are found in shale and siltstone that contain volcanic ash radiometrically dated at 70 million years.

Any Triceratops found below the volcanic ash may be a little older than 70 million years, and any found above may be a little younger than 70 million years. The age of the Triceratops can be determined more closely than that of the acritarchs and bacteria and that of the trilobites because the rock unit that contains the Triceratops can itself be radiometrically dated, whereas that of the other fossils could not.

Based on the Rule of Superposition, certain organisms clearly lived before others, during certain geologic times. The narrower a range of time that an animal lived, the better it is as an index of a specific time. No bones about it, fossils are important age markers. But the most accurate forms of absolute age dating are radiometric methods. This method works because some unstable radioactive isotopes of some elements decay at a known rate into daughter products.

This rate of decay is called a half-life. Half-life simply means the amount of time it takes for half of a remaining particular isotope to decay to a daughter product. Good discussion from the US Geological Survey: So geochronolgists just measure the ratio of the remaining parent atom to the amount of daughter and voila, they know how long the molecule has been hanging out decaying.

There are a couple catches, of course. Not all rocks have radioactive elements.

## Radiometric dating

Sedimentary rocks in particular are notoriously radioactive-free zones. So to date those, geologists look for layers like volcanic ash that might be sandwiched between the sedimentary layers, and that tend to have radioactive elements.

You might have noticed that many of the oldest age dates come from a mineral called zircon. Each radioactive isotope works best for particular applications. The half-life of carbon 14, for example, is 5, years. On the other hand, the half-life of the isotope potassium 40 as it decays to argon is 1.