1. Unit 3 Earth History: Day 7 Focus: Absolute Age/Half-Life
12/14/18
Pick up the lab sheet on the front lab table.
Do this warm-up on page 57 under the e.q.
Order from
oldest to youngest.
2.What is D?
3.What is C?
4.What is A?
D is a fault.
C is an igneous intrusion.
A is an unconformity.

2. Plan for the Day 1. Finish notes on Absolute Age-Dating of Rock
*Hands-on activity modeling half-life
*Brainpop Video- Carbon-14
2. Half-life Practice Problems Worksheet

3. Homework a. Uniformitarianism/Catastrophism b. Law of Superposition
Half-Life Practice Problems wkst. – due Monday
2. Make flash cards 6-8 due Monday
***CFA Monday over:
a. Uniformitarianism/Catastrophism
b. Law of Superposition
c. Law of Cross-Cutting Relationships
d. Relative age-dating of rocks
e. Index Fossils
f. Absolute age-dating of rocks
Homework

4. Earth History Theories
Uniformitarianism – James Hutton
Earth is much older (maybe billions of years) than previously thought.
Most geologic change is gradual/slow (processes like erosion and deposition)
Same processes that shape Earth’s surface today also shaped it in the past
2. Catastrophism – The Church and most scientists of Hutton’s time
Earth is only a few thousand years old –young
Most geologic change is a result of rare, sudden, catastrophic events (earthquakes, asteroid impacts, volcanoes, floods)
Quick changes to Earth’s surface features

5. How can elements in rocks help us know the exact age of those rocks?
Essential Question –
How can elements in rocks help us know the exact age of those rocks?

6. Igneous rocks contain radioactive elements that “decay” or change over time.

7. Isotopes
Isotopes are atoms of the same element (same # of protons), that have a different #of neutrons. (This gives it a different atomic mass) Some isotopes are RADIOACTIVE

8. Uranium isotopes are radioactive… this means they are unstable and will “decay” (change) over time into more stable elements. As they “decay”, they give off heat.

9. Over time…a long time… they decay

10. Radioactive Decay
Radioactive decay, simply put, is a process by which radioactive isotopes become stable isotopes (not radioactive anymore).
Radioactive/unstable
Stable

11. Parent vs. Daughter
The radioactive isotopes are called PARENT ISOTOPES .
The stable, decayed isotopes are called DAUGHTER ISOTOPES.

12. Vocabulary
7.Half-life: The rate of decay of radioactive elements (isotopes)…the amount of time it takes for 1/2 of the radioactive (unstable) element in an igneous rock to decay (change) into a stable (non-radioactive) element.
A.D. 1 -As the radioactive (unstable-PARENT) element decreases, the non-radioactive (stable- DAUGHTER) element increases
A.D 2- This rate is constant & never changes.

13. Parent Vs Daughter
Daughter
Parent

14. Radioactive Decay and Half-Life
“Parent” element ”Daughter” element
After four half-lives, only 1/16th of the parent element remains; the rest of it has decayed into daughter element.
After one half-life, only one-half (1/2) of the parent element remains; half of it has decayed into daughter element.
After two half-lives, only 1/4th of the parent element remains; ¾ of it has decayed into daughter element.
After three half-lives, only 1/8th of the parent element remains; 7/8 of it has decayed into daughter element.
Igneous rock first forms-100% parent element
***Assuming the parent element has a rate of decay (half-life) of 10,000 years

16. Vocabulary Continued
8.Radiometric dating : method used to determine the absolute (exact) age of rocks and fossils.
A.D. 1 -used primarily to date igneous rocks (intrusions)
A.D. 2 -can only date particles in sedimentary rock, but not the whole rock layer – Why do you think?
A.D Carbon-14 dating allows scientists to know the exact (absolute) age of things that were once living. (bones, teeth, etc.) (You have to know this one.) ***Please add this – half-life is 5,730 years. Memorize it!

17. Let’s do a hands-on activity to model radioactive decay
Let’s do a hands-on activity to model radioactive decay. You will work with the person beside you. In this simulation, goldfish will represent the parent element (radioactive unstable). Cheerios (very old…DO NOT EAT) will represent the daughter element (stable). Listen for directions. Complete your own half-life worksheet as we do the activity together. After the activity, there is a recap at the bottom on your notes. Work with your partner to fill it in. If you don’t finish it in class, finish it for homework.

18. Re-cap…Scientists can use radiometric dating methods to determine the ___________ age of fossils and __________ rocks.
When a new igneous rock forms, it has different elements in it. Some of the atoms of those elements are unstable (isotopes) and will “______”(break down over time) into atoms of stable elements. The unstable element is called the _______ element. The stable element is called the ________ element. Each unstable element has its own unique rate of decay which is constant. This rate of decay is called a __________. If scientists know the half-life of an element, they can tell how old the rock is based on _______________________ still remains in the rock and _________________________is present.
absolute
igneous
decay
parent
daughter
half-life
how much parent element
how much daughter element

19. Answers at the bottom of your activity:
*As a rock gets older, the amount of parent (radioactive/unstable) element (1)__________ and the amount of daughter (stable) element (2)___________.
An older rock has more (3)________ element, and a younger rock has more (4)________ element.
With every half-life that passes, the parent element decreases by (5)________.
After 1 half-life, (6)_____ of the parent element is present. After 2 half-lives, (7)_______ of the parent element is present. After 3 half-lives, (8)______ of the parent element is present.
decreases
increases
daughter
parent
one-half
1/2
1/4
1/8

20. Let’s see what Brainpop has to say about Absolute Dating using Carbon-14. You will need to know the rate of decay for Carbon-14 and that it is used to date once-living things, not rocks.
Brainpop on Carbon Dating

21. Let’s do one more half-life practice activity:
a. Brainpop - calculator

22. Wrap-up:
What percentage of radioactive –PARENT- element would remain in a rock sample after one half-life? Two half-lives?