1. Absolute Ages of Rock
Mr. Perez

2. Important vocabulary Isotopes Radioactive decay Half-life
Radiometric dating
Uniformitarianism

3. Absolute Ages
Absolute age is the age, in years, of a rock or other object.
Examples:
How old are you?
How old is your house?
How old is your book bag?
How old is your pet?
How old is your sibling?

4. Radioactive Decay Atoms are made up of:
Nucleus- central region
Includes the protons (+) and neutrons (0)
Electrons- cloud surrounding center (-)
The number of protons(+) determines the identity of the element
The number of neutrons (0) determines the form of the element (aka isotope)

5. Radioactive Decay
Some isotopes are unstable and break down into other isotopes and particles
We call the above process radioactive decay

6. Radioactive Decay- Alpha and Beta Decay
Neutron breaks down into proton and electron
Electron leaves atoms a beta particle
Alpha Decay
Two protons and two neutrons are given off
Leave as alpha particle
Both types of decay form a new isotope

7. Radiometric Decay- Half Life
Each parent isotope decays (breaks down) into its daughter isotope at a certain rate
Based on this decay rate, it takes a certain period of time for one half of the parent isotope to decay to its daughter product
The half-life of an isotope is the time it takes for half of the atoms in the isotope to decay.
Example- It takes carbon-14 5,730 years for half of its atoms to turn into nitrogen-14. Then, it takes another 5,730 years for half of the remaining carbon-14 atoms to turn into nitrogen-14, and so on…
THINK OF EXPONENTS! 23 = 8, 32 = 9, 44 = 256

8. Radioactive Decay- Half-life
Fill in the following table using this information:
Mr. Perez has 100g of carbon-14. After 5,730 years, how many grams of carbon-14 will still be carbon-14? After 2? After 3?...
Year
Grams of carbon-14
100g 1 2 3 4

9. Radiometric Dating

10. Radiometric Dating
By measuring the ratio of parent isotope to daughter product in a mineral AND knowing the half-life of the parent, you can calculate the absolute age of a rock
This is called radiometric dating
A scientist must decided which parent isotope to use when measuring the age of a rock.
If it’s old, the scientist will use an isotope with a long half-life
Example: potassium-40 takes 1.25 billion years to decay to argon-40
To avoid errors, conditions must be met for ratios to give a correct indication of age:
The rock being studied must retain ALL of the argon-40 that produced by the decay of potassium-40
It cannot contain any contamination of daughter product from other sources

11. Radiometric Dating- Radiocarbon Dating
Carbon-14 is useful for dating bones, wood and charcoal up to 75,000 years old.
Living things take in carbon from the environment to build their bodies
Most of this carbon is carbon-12, but some is carbon-14
The radio of these two isotopes is always the same
After an organism dies, the carbon-14 decays slowly
By determining the amounts of isotopes in a sample, scientists can evaluate how much the isotope ratio differs from that in the environment

12. Radiometric Dating- Radiocarbon Datin

13. Radiometric Dating- Age Determinations The Oldest Known Rocks
Rocks that can be radiometrically dated are mostly IGNEOUS and METAMORPHIC rock
Sedimentary rocks cannot be dated by carbon-14 because they are made up of particles eroded from older rocks
The Oldest Known Rocks
Using radiometric dating, the oldest rocks on Earth are about 3.96 billion years old
The Earth is about billion years old

15. Uniformitarianism James Hutton (Scottish scientist in the 1700s)
Estimated that the Earth is much older than we think
Uniformitarianism- principle that states that Earth’s processes occurring today are similar to those that occurred in the past
“The present is the key to the past”
Today, scientists recognize that Earth has been shaped by two types of change
Slow, everyday processes that take place over millions of years
Violent and unusual events

16. Videos

17. Glencoe Science & McGraw Hill Publishing
Resources
Florida Science Grade 7
Glencoe Science & McGraw Hill Publishing
Google Images