1. Hello Studiers of the Earth!
DQ: Place these rock layers in order from oldest to youngest
Today:
Go Over Rock Strata Practice
One More Time…
Absolute Time

2. How about this one? OR B A A B D D E E C C

3. MEASURING ABSOLUTE TIME
TREE RINGS
EACH RING REPRESENTS A SINGLE YEAR (SPRING/FALL) THE WIDTH OF THE RING DEPENDS UPON THE TEMPERATURE AND RAINFALL
VARVES
GLACIAL LAKE DEPOSITS. A THICK LIGHT COLORED LAYER IN THE SUMMER AND A THIN DARK LAYER IN THE WINTER

4. RADIOMETRIC DATING
USED TO DETERMINE AGES OF OBJECTS THAT ORIGINATED FAR BACK IN TIME. CERTAIN ROCKS CONTAIN RADIOACTIVE ISOTOPES
RADIOACTIVE ISOTOPES ARE ATOMS OF ELEMENTS THAT GIVE OFF RADIATION FROM THEIR NUCLEI
RADIOACTIVE DECAY IS THE PROCESS BY WHICH A RADIOACTIVE ISOTOPE CHANGES INTO A NEW STABLE ELEMENT

5. But Wait!!! – How does this work?
Atoms always have the same number of protons but can have different numbers of neutrons
Example: Carbon
Always has 6 protons
Can have different numbers of Neutrons
Each of these is an isotope of carbon
SOURCE:sjsugeology.org/.../powerpoint/Petsche_Relative_and_Absolute_Dating.

6. Absolute Dating: Big Ideas
Some isotopes are unstable (radioactive)
They decay or change into something else by losing parts of the atom
Radioactive isotopes change from one form to another at a steady pace
We call the original (unstable) isotope the parent isotope and the new form the daughter isotope

7. Absolute Dating: Big Ideas
Half-Life is the time it takes for half of the original, unstable isotope of the element (parent) to change into the daughter isotope
Different radioactive isotopes decay at different rates
We can figure out how old a sample is by comparing the amount of parent material to the amount of daughter material and calculating the number of half-lives (half-lifes?) it takes to get that ratio

8. Absolute Dating: Big Ideas
For radioactivity dating we use igneous rocks and minerals. The clock starts when radioactive atoms that are present in the magma get incorporated in the crystalline structure of certain minerals in the rocks.
The crystals containing the parent atoms form and so we then have a “container” with parents that can begin decaying to form daughters.
We can then use measure the parent-daughter ratio. This is our “atomic clock” that records the time since the rock crystallized.
Figure 17.21: (a) Magma contains both radioactive and stable atoms. (b) As magma cools and begins to crystallize, some radioactive atoms are incorporated into certain minerals because they are the right size and can fit into the crystal structure. Therefore, at the time of crystallization, the mineral will contain 100% radioactive parent atoms and 0% stable daughter atoms. (c) After one half-life, 50% of the radioactive parent atoms will have decayed to stable daughter atoms.
M&W4 Fig ; M&W5 Fig
SOURCE:sjsugeology.org/.../powerpoint/Petsche_Relative_and_Absolute_Dating.

9. Absolute Dating: Big Ideas
C14 is an isotope of carbon that forms from Nitrogen in the atmosphere. Living things consume this radioactive carbon.
Once dead, no new carbon is absorbed, and C14 turns back into Nitrogen.
The Half-Life of C14 is 5,730 years.
This method works best for fossils younger than 50,000 years. Why?
SOURCE:sjsugeology.org/.../powerpoint/Petsche_Relative_and_Absolute_Dating.
M&W4 Fig ; M&W5 Fig

10. Rate of Decay
The composition of rock containing radioactive elements changes slowly over time.
The amount of radioactive element decreases while the amount of new element increases.
The rate of decay for a specific element is constant.
The half-life of an element is the time it takes for half of the radioactive atoms to decay.
SOURCE: teachers.mvwsd.org/.

11. Example Isotope A has a half life of 999 years
How long will it take for a 4 gram sample of Isotope A to decay to 1 grams of A and 3 grams of daughter material?
Well…
After 999 years there will be 2 grams of A and 2 grams of daughter material
After another 999 years, there will be 1 gram of A and 3 grams of daughter material
999
999

12. Another one… Radium-226 has a half-life of 1,600 years.
If we start out with 8000 atoms of radium-226, how much would be left after 3,200 years?

15. Divisions of Geologic Time
Eras are subdivided into periods...periods are subdivided into epochs.
Era
Period
Epoch
E + P = EP

17. Divisions of Geologic Time
Geological time begins with Precambrian Time. Precambrian time covers approximately 88% of Earth’s history.

19. FOUR Eras… PRE-CAMBRIAN – 88% of earth’s history
Paleozoic (ancient life)
544 million years ago…lasted 300 million yrs
Mesozoic (middle life)
245 million years ago…lasted 180 million yrs
Cenozoic (recent life)
65 million years ago…continues through present day

20. Today…
Today we are in the Holocene Epoch of the Quaternary Period of the Cenozoic Era.
Which unit is the largest?
Which unit is the smallest?

21. Today…
Today we are in the Holocene Epoch of the Quaternary Period of the Cenozoic Era.
Which unit is the largest?
Which unit is the smallest?