1. Relative vs. Absolute Dating
Magazines can be piled up and you can know the relative age of the magazine by observing the order in which the magazines were stacked
Absolute dating is a process that uses the properties of atoms in rocks and other materials to determine a more accurate age of rock layers

2. What are Atoms and Elements?
Atoms are the particles or “building blocks” of which all matter is composed
Atoms combine, like blocks snapping together, to form many different types of matter.
Specific types of atoms are called elements (i.e. oxygen, carbon, gold, etc.)
Some atoms “fall apart” or change over time

3. Three basic particles make up an atom
Protons, Neutrons, and Electrons:
In the nucleus:
Protons: Particles that have a positive electrical charge Larger than neutrons
Neutrons: Particles that have no electrical charge Smaller than protons
The nucleus has a positive charge
Around the Nucleus:
Electrons: Negatively charged particles that move around the nucleus Smallest of particles
There is one electron for each proton

4. Atom Diagram Nucleus (contains Protons & Neutrons) Electrons
(move around the Nucleus)

5. Special Atoms: Isotopes
If the amount of protons in an atom changes, a new element is formed
e.g. Carbon has 6 protons; Nitrogen has 7 protons
However, if the number of neutrons are changed, the type of element is not changed
e.g. Carbon can continue to exist with different amounts of neutrons (Carbon-14 indicates the total of protons and neutrons. It still has 6 protons)
Atoms of the same element that have an unusual number of neutrons are called isotopes
Isotopes are unstable atoms
e.g. Carbon-14 is an unstable Carbon atom or isotope

6. Unstable Isotopes break down
In a process known as radioactive decay,
One of the isotopes neutrons breaks down, changing into a proton and an electron
Some isotopes give off two protons and two neutrons in the form of an alpha particle (see diagram-one after next slide)
The electron leaves the atom as a beta particle (see diagram-one after next slide)
The nucleus loses a neutron but gains a proton
In the end, a new element is formed

7. Radioactive Decay Diagram
Decay of: neutrons 2-protons 1 2 3
Uranium-238
Lead-206 (eventually)
Uranium-238 decays by emitting alpha particles (two protons and two neutrons) and beta particles (one electron). A beta particle is produced when a neutron decays and becomes a proton.

8. Similar Chart: Uranium-238 to Lead-206
The decaying process is complex but scientists believe the process follows a pattern
You do not need to memorize or understand this chart

9. Radioactive Decay Example
When atoms of the radioactive isotope uranium-238 decay, they eventually form atoms of lead-206
Lead-206 is not radioactive, so it will not decay any further
In this example, uranium-238 is known as the parent material, and lead-206 is known as the daughter product

10. Radioactive decay is measured by the material’s “Half-Life”
The half-life is the rate, or speed, at which the radioactive parent material decays into its daughter product
The half-life is the total amount time it takes for half of the atoms in the material to decay
Different isotopes decay at different rates
“Whole-life”
“Half-life”

11. Half-Life Example Parent material: Carbon-14
1st 5,730 yrs.
Parent material: Carbon-14
It takes 5,730 years for half of the Carbon-14 material to decay into its daughter product Nitrogen-14
Then, it takes another 5,730 years for ½ of the remaining Carbon-14 material to decay
Therefore, after 2 half lives, ¼ of the original carbon-14 atoms still remain
And, after 3 half lives, 1/8 of the original carbon-14 atoms still remain
Nitrogen-14
2nd 5,730 yrs.
Carbon-14
Nitrogen-14
Nitrogen-14

12. Half-Life Sequence diagram
Eventually, such a small amount of the parent material is left that it
may not be measureable.
Note: There is no time period identified in this example. Yet, the half-life, or period of decay, remains the same between each half-life

13. Radiometric Dating
To a geologist, the decay of radioactive isotopes is like a clock ticking away, keeping track of time that’s passed since rocks have formed
As time passes, the amount of parent material in a rock decreases as the amount of daughter product increases
A geologist can calculate the absolute age of a rock by measuring:
the amount of parent and daughter materials in a rock
and knowing the half-life of the parent

14. Radiometric Dating is Absolute Dating…with Limitations
Carbon-14 is useful for dating fossils, bones, and wood up to 50,000 years old
Rock that can be radiometrically dated are mostly igneous and some recrystallized metamorphic rocks
Only some sedimentary rock
The amount of starting material can come into question
Decay rates are assumed to be uniform over time
Radiometric dating has been used to date the oldest rocks found on Earth (3.96 billion years old)
Scientists have estimated the age of Earth at 4.6 billion years