1. Geologic History

2. Geologic Time Scale

3. Geologic Time Scale
Chart of Earth’s history showing events, time units, & ages
Era: the four largest subdivisions of the geologic time scale – Precambrian, Paleozoic, Mesozoic, Cenozoic
Period: subdivisions of eras on the geologic time scale
Epoch: subdivisions of periods on the geologic time scale – ONLY in the Cenozoic

5. Traces from our past
Index Fossils: a fossil of a species that existed briefly and was widespread geographically, used in determining the relative age of rock layers (i.e. trilobites)
Fossils and Ancient Environments: fossils can be used to determine what the environment of an area was like long ago.

6. Traces from our past
Fossils: the remains or traces of a once-living organism preserved in rock.
How fossils form:
organisms have a better chance of being preserved if they have hard parts (bones, shells, teeth, or wood)
usually found in sedimentary rocks

7. Petrified Remains
Petrified Remains – plant or animal remains that have been turned to rock; this happens when minerals carried in groundwater replace the original material.

8. Petrified Wood

10. Carbonaceous Film
Carbonaceous Film – a fossil impression in a rock, consisting only of a thin carbon deposit

11. Mold and Cast
Mold – a cavity in a rock that has the shape of a fossil that was trapped there; water dissolved the fossil away, leaving its imprint

12. Mold and Cast
Cast – type of fossil formed when an earlier fossil in rock is dissolved away, leaving behind the impression of that fossil, and new sediments or minerals enter the mold

13. Original Remains
Original Remains – sometimes the actual organism or parts of organisms are found (mosquitoes in amber, wooly mammoth frozen in ice)

14. Trace Fossil
Trace Fossil – footprints, worm holes, burrows & other traces of animal activity preserved in rock

15. Trace Fossil

16. Geologic Time Scale

17. Age Dating Techniques
Relative Dating: determining the order of events and the relative ages of rocks by examining the positions of rocks in layers

18. Age Dating Techniques
Relative Dating – another good diagram

19. Uniformitarianism
In 1795, James Hutton described a ‘new concept’ stating that:
The geologic processes now at work were also active in the past.
The present physical features of Earth were formed by these same process, at work over very long periods of time
“the present is the key to the past”

20. Relative Dating
Law of Original Horizontality: sediments are deposited in a horizontal fashion  

21. Relative Dating
Law of Superposition: in layers of undisturbed rock, the oldest are on the bottom, and rocks become younger toward the top

22. Law of Superposition

23. Relative dating
Law of Cross-Cutting Relationships: igneous rock intrusions or faults are younger than the rocks that have been intruded or faulted

25. Relative Dating
Law of Included Fragments: pieces of one rock found in another rock must be older than the rock in which they are found

26. Relative Dating
Correlation: the matching of rock layers from one area to another to establish a relative date

27. Relative Dating
Unconformity: one or more missing layers in a sequence of rocks, this is the result of gaps in the time/rock record
angular unconformity – tilted rock layers meet horizontal rock layers, this indicates layers are missing and there is a gap in the time record
disconformity – the top rock layer is eroded before the next layer can be deposited causing a gap in the time record

28. Angular Unconformity

29. Angular Unconformity

30. Disconformity

31. Disconformity

33. Age Dating Techniques
Absolute Dating: determining the age of rocks using the radioactive decay of atoms.
Radiometric Dating: an Absolute Dating method that uses the rate of decay of radioactive isotopes in rocks.

34. Age Dating Techniques
Radioactive Decay: the decay of an atom of one element to form another element, occurring when an alpha particle or beta particle is expelled from the original atom (Ex. parent atom (K) decays to daughter product (Ar))
Half-Life: the time it takes for half of the parent atoms of an isotope in an object to decay into the daughter product (K-Ar = 1.3 billion years)

35. Age Dating Techniques
Tree rings – counting the number of rings on a cross section of a tree
Radio-Carbon dating – the radioactive carbon isotope used for dating organic material:
Carbon 14  decays to  Carbon 12
The ‘half life’ of Carbon 14 is 5700 years…
Half life – how long it takes for half of the material to decay

37. Precambrian Time from 4.6bya to 545mya
makes up ~90% of Earth’s history
very little is known about fossils from this period
cyanobacteria appeared around 3.5 bya
responsible for oxygen and
indirectly for ozone in
the atmosphere
invertebrates developed
at end of era

38. Paleozoic Era: 545mya to 245mya
began when animals developed hard parts that could be fossilized
life moved from ocean to land
end signified by mass extinction probably caused by formation of Pangaea
Early - “Age of the Invertebrates”
Late – “Age of the Plants”
Paleozoic Era:

39. Mesozoic Era
245 mya to 66 mya
Laurasia & Gondwanaland developed from the break-up of Pangaea
Reptilian eggs developed a hard shell
Dinosaurs evolved during the Triassic and dominated during the Jurassic and Cretaceous periods

40. Mesozoic Era (cont.) “Age of the Reptiles” (Dinosaurs)
Mammals appeared during the Triassic
Birds appeared during the Jurassic
Angiosperms appeared during the Cretaceous
End signified by mass extinction
“Age of the Reptiles” (Dinosaurs)

41. Cenozoic Era 66mya to present
Increased tectonics created the Alps, Himalayas, and the Appalachians
Global temperature drop
Mammals evolved and
dominated
Homo sapiens emerged
500,000yrs. ago
“Age of the Mammals”

43. Evolution Organic Evolution: gradual change in life-forms through time
Species: group of organisms similar to each other and that typically reproduce only with each other.
Natural Selection: natural process by which some organisms survive and reproduce because they have traits favorable to survival in an environment, while others die out because they lack those traits

44. Evolution
Endangered: describes a species that has a small number living and thus in danger of dying out
Habitat: any place where organisms live, grow, and interact

45. General Related Facts – (the amazing impact humans have had)
Four years ago 19,836sq. km. of Amazon rainforest was destroyed
More than 80% of all deforestation of the Amazon has occurred since 1980
More than ¼ of all pharmaceuticals come from rainforest plants

46. General Related Facts – (the amazing impact humans have had)
only 22% of Earth original forest coverage remains…..
Western Europe lost 98% of its primary forests;
Asia 94%;
Africa 92%;
N. America 66%;
S. America 54%