1. Earth History

2. True or False: “The caveman had dinosaur for breakfast.”?
Humans and dinosaurs never lived at the same time… BUT HOW DO WE KNOW??

3. Earth History: the study of the changes that have occurred on Earth since its origin
Earth has been around for a LONG TIME! Check ESRT p.8

4. Earth formed about 4600 million year ago…
That’s 4.6 billion years ago!
There was no life then
Earth was a big ball of magma! Too hot for life!!

5. The Precambrian Eon: 4.6 b.y.a to about 550 million years ago (m.y.a.)
Simple life forms in oceans
Oxygen forms and enters atmosphere

6. Life on Earth in the Precambrian: Simple life forms
The Precambrian is the MAJORITY of earth history…
Over 4 billion years!
But NOT MUCH HAPPENED!

7. NY State in the Precambrian:
Grenville Orogeny forms Adirondack rocks!
Grenville mountains also form!

8. The Paleozoic Era:
542 m.y.a. to 251 m.y.a.
Divided into 6 periods
Life mostly still in ocean
Lots of fish and amphibians

9. NY State in the Precambrian:
Fossils include trilobites and eurypterids (the NYS fossil)
Continents collide to form mountains
Orogeny: mountain building activity!

10. The Mesozoic Era:
The “age of the reptiles” including the rise (and extinction) of dinosaurs
Fill in your notes!

11. The Cenozoic Era:
The “age of the mammals” including the rise of humans
Fill in your notes!

12. Geologic eras are defined by the conditions on Earth at that time…
Organisms evolve to fit the changing conditions!
And mammals rule the Cenozoic!

13. The fossil record shows how life has evolved
Some organisms dominate as conditions change 
Others die off and become extinct 

14. Pangaea begins to break up about 200m.y.a.
Continents are still separating at Mid Ocean Ridge
Conditions on Earth continue to change!
What does the future hold??

15. Most of Earth’s history was the Precambrian
There is very little fossil evidence for 4 billion years! That’s 87% of Earth History!
Most life evolved only in the past 0.5 my!

16. Landscape Regions of NYS
SILURIAN
DEVONIAN
CRETACEOUS

17. Ages of the rocks of NYS
SILURIAN
DEVONIAN
CRETACEOUS

18. Knowing EXACTLY how old rocks are This is done with RADIOACTIVE DATING
Absolute Age
Knowing EXACTLY how old rocks are
This is done with RADIOACTIVE DATING
Radioactive elements decay according to their half life.
The half-life tells how long the rock has been around- this is its age!

19. Carbon-14 has a half-life of _______ years
After 5700 years half of the carbon decays
This is one half-life!
The decay process continues! 
12.5g
100g 
50g 
25g
This process tells us the rock’s absolute age!

20. C-14 is used to date young rocks Because it has a SHORT half-life
and organic remains
Because it has a SHORT half-life .

21. Other isotopes are used to date OLD rocks
Half Life
Other isotopes are used to date OLD rocks
Because they have LONG half-lifes .

22. Decay of Unstable Isotope
Draw the generic graph for the
half-life of a radioactive isotope.
New Isotope forming
Decay of Unstable Isotope

23. Earth History: the study of the changes that have occurred on Earth
Earth has been around for a LONG TIME! Check ESRT p.8

24. Fossils Fossils: Remains of past life preserved in bedrock!
Can be the actual organism (plant or animal)
Can be an impression left by the organism
Shells, bones and plant stems make the best fossils because they are more durable!

25. Fossils Fossils ONLY form in SEDIMENTARY rock… WHY?
The organism (plant or animal) must be buried in sediments to fossilize
Fossils are usually found in…
Very fine grained clastic sedimentary rock
Ex: Shale and siltstone
Crystalline or bioclastic chemical sed. rock
Ex: Limestone
Fossils are DESTROYED when rocks are metamorphosed or melted!

26. Fossils Fossils that are used to date rock are called INDEX fossils
From organisms that…
Lived only a short period of time
Lived over a widespread area
Ex: Placoderm Fish lived all over NY State during what Period? (see ESRT)
Index fossils tell us the age of bedrock in which they are located!

27. Fossils
Using index fossils to date bedrock outcrop layers is called correlation!
Layer 3 in each outcrop contains the same index fossil- they are the SAME AGE!
Which other
rock layers are
the same age in
both outcrops?

28. Fossils Layer 1 is older than layer 3! Why??
1 contains index fossil “A” from ESRT
Outcrop 3 contains index fossil Z!
Fossil A is older than fossil Z!

29. Fossils Missing rock layers! Why is there no layer 5 on the left?
What layers are missing on the right side? Why?

30. The Law of Superposition
The rock layers in this outcrop are sedimentary
These layers are undisturbed…
Not tilted, faulted or overturned
The bottom layer is the oldest
The top layer is the youngest
The bottom layer formed first and is the oldest
youngest
oldest

31. The Law of Superposition
This is RELATIVE DATING
One layer is older compared to another
Relative dating…
A is older than B
B is older than C
C is older than A
D is the youngest
youngest
oldest

32. Relative Dating Older Younger A fault in the outcrop
Goes through all the layers…
Rock layers are all older than the fault!
The tilting also happened after the rocks formed!
Relative Dating in action!
Older
Younger

33. Relative Dating Layer “S” and “F” have been cut by a fault!
They are both older than the fault!
Layer “L” is youngest!
It’s on top and not affected by fault

34. Relative Dating Younger Magma intrudes into sedimentary layers…
Solidifies into igneous rock
Igneous rock is younger than the sedimentary layers!
Relative Dating in action!
Younger

35. Relative Dating Magma intrudes into sedimentary layers…
Contact metamorphic rock forms where magma touches the older layers

36. Relative Dating Contact metamorphic rock on D
D is older than C!
No contact metamorphic rock on B
B formed after C and is younger
A is younger than B

37. Relative Dating B formed after C C formed as an igneous EXTRUSION
Because it formed outside!
Extrusions are older than the layers above it

38. Relative Dating H is an intrusion D is an extrusion
contact metamorphic on all sides
It’s younger than all layers except “S”
D is an extrusion
No contact metamorphic on top
It’s older than layer “S”

39. Relative Dating Layer “A” is the oldest in the outcrop
“M” formed next, then “E” and then “L”
Igneous rocks “D” and “H” formed next
“L” and “D” were eroded flat (“C”)
Then layer “S” formed on top
Layer “S” is the youngest

40. Uncomformity Unconformity is a buried erosion surface
Missing rock layers removed by erosion
“C” is the unconformity in this outcrop
Layer “L” and “D” were eroded
“S” formed after the erosion
Layer “S” is the youngest

41. Uncomformity Date the unconformity… Layer A is Permian
Layers M and E are Triassic
Layer L is Cretaceous
Layer S is Quaternary
The unconformity is neogene/paleogene

42. Unconformity What kind of rock is shown in each layer?
The layers are all flat which means they are all what type of rock?
Is it possible that there are fossils in this outcrop?