1. Warm up Read the sentence and circle one of the words in parenthesis:
Earth is (old/young) and has (remained the same/ changed) over time.

2. Earth formed about 4.6 billion years ago.
The History of Life
Earth formed about 4.6 billion years ago.
Gravity pulled the densest elements to the center of the planet.
After about 500 million years, a solid crust formed on the surface.

3. Earths early Atmosphere had little to no Oxygen.
The History of Life
PLANTS
Atmosphere
The gases that likely made up the atmosphere are those that were expelled by volcanoes.
Water vapor (H2O)
Carbon dioxide (CO2)
Earths early Atmosphere had little to no Oxygen.
Sulfur dioxide (SO2)
Carbon monoxide (CO)
Hydrogen sulfide (H2S)
Hydrogen cyanide (HCN)
Nitrogen (N2)
Hydrogen (H2)

4. Chapter 14
The History of Life
14.1 Fossil Evidence of Change
Plate tectonics describes the movement of several large plates that make up the surface of Earth.
These plates, some of which contain continents, move atop a partially molten layer of rock underneath them.

5. A fossil is any preserved evidence of an organism.
The History of Life
Evidence of Change
A fossil is any preserved evidence of an organism.
Most organisms decompose before they have a chance to become fossilized.

6. Most fossils are formed in sedimentary rock.
The History of Life
Fossil Formation
Most fossils are formed in sedimentary rock.
The sediments build up until they cover the organism’s remains.
Minerals replace the organic matter or fill the empty pore spaces of the organism.

7. Dating Fossils
Relative dating
Absolute Dating
Radiometric dating

8. Younger layers are deposited on top of older layers.
The History of Life
Relative dating
Used to determine the age of rocks by comparing them with those in other layers.
Law of superposition
Younger layers are deposited on top of older layers.

9. Uses the decay of radioactive isotopes to measure the age of a rock
The History of Life
Radiometric Dating
Uses the decay of radioactive isotopes to measure the age of a rock
Uses an isotopes half- life:
Time it takes for half to decay
Radioactive isotopes that can be
used for radiometric dating are found only in
igneous or metamorphic rocks.
Why can’t this method be used to date most fossils?

10. EXAMPLE: A 100 gram sample of radioactive Uranium 235 (U235) would decay into 50 grams of U235 in about 713 million years, and then to 25 grams of U235 in another 713 million years (a total of 1,426 million years for those two half-lives).
Therefore, the half-life for U235 is 713 million years (0.713 billion years).
GRAPH!
TIME
U 235
100 g
1 half-life
50 g
2 half-lives
25 g
3 half-lives
12.5 g

12. U235 Pb 207 GRAPH! As U235 decays it is converted to Pb 207. TIME
1 half-life
50 g
2 half-lives
25 g
75 g
3 half-lives
12.5 g
87.5 g
GRAPH!

15. Deep Time Activity

16. Which dating method determines the age of
The History of Life
Which dating method determines the age of
rocks by comparing them to rocks in other
layers?
absolute dating
geological dating
relative dating
sedimentary dating

17. Which is the half-life of the radioactive isotope
shown in the graph?
18 years
36 years
54 years
72 years

18. Study the graph. Determine the age of a rock if
it contained 40% C-14.
2,857.5 years
7,576 years
11,460 years
5,730 years

19. What gas do scientists think was absent from Earth’s early atmosphere?
Chapter 14
The History of Life
What gas do scientists think was absent from
Earth’s early atmosphere?
sulfur
nitrogen
oxygen
water vapor

20. Beryllium-10 (Be-10) has a half life of about
1.5 million years. If a sample is analyzed and
determined to contain ¼ of the original Be-10,
what is the age of the sample?
750,000 years
3 million years
4.5 million years
6 million years

21. In which type of rock do paleontologists search for fossils?
The History of Life
In which type of rock do paleontologists search
for fossils?
igneous
metamorphic
sedimentary
volcanic

22. Closing
Describe each of the following:
Relative dating
Radiometric dating