1. Physical Science
Geologic Time

2. Observations Regarding Rock Layers
Relative Dating – Lower layers of sedimentary rock are formed before older layers.
Original Horizontality – layers of sediment deposited evenly with new layers on top of old layers.
Superposition – upper layers are younger than lower layers
Any incline is an indication of a disturbance after deposition.

3. Earth History
Cross Cutting – an igneous intrusion or fault that cuts through preexisting rock. This intrusion will be younger than the rock through which it cuts.

4. Earth History
Inclusion – pieces of one rock type contained within another – any inclusion is older than the rock containing it.

5. Earth History
Faunal succession – Fossils contained within rock can indicate that they were in existence around the time the rock was formed. This succession of fossils gives rise to the evolutionary nature of species.

6. Earth History
Unconfomities – break up points of the original sediment layers
Angular unconformity – tilted or folded rock layers that become overlain by younger horizontal layers.
Nonconformity – sedimentary rock that are depositeed over and eroded surface of metamorphic or intrusive igneous rock.
from yahoo images

7. Earth History

8. How do we know how old a rock layer is?
Radiometric dating – using half life of isotopes to determine the age of layers
Fossil found in layers – certain fossils seem to have only been around at certain times
from yahoo images

10. Earth History

11. Precambrian 4.6 billion years to 544 million years ago
Makes up about 85 % of the earths history
Most rocks have been eroded away, metamorphosed or recycled
Seems to have had lots of volcanoes and meteor hits
Simple organisms existed (stomatolites, blue green algae)
They used carbon dioxide and produced oxygen
Fossils in Australia are of jellyfish and worm type

12. Paleozoic
Cambrian
Fossils of all major groups of marine organisms are found
Some organisms secreted calcium carbonate and calcium phosphate to form outer skeletons or shells
Trilobites are from this time period

13. Paleozoic
Ordovician
Abundant marine life
Appearance of vertebrates

14. Paleozoic Silurian Most of North America rose above sea level
This caused gypsum and other deposits to accumulate in the receding seas
Terrestrial plants flourished – in wet lands
Air breathing scorpions and millipede fossils are found

15. Paleozoic Devonian Called the Age of Fishes
Lowland forests and seed trees appear
Lungfish appear
First amphibian fossils appear
These creatures could live on land but laid eggs in the water

16. Paleozoic Carboniferous Mississippian and Pennsylvanian periods
Warm climate – lush vegetation
These swamps created the coal beds that lie under North America, Europe, and China.
Giant cockroaches and dragonflies (80cm wing span)
First reptiles (anapsids) appear
First egg formation – life existed solely on land

17. Paleozoic Permian Reptiles existed for 200 million years
Two more reptiles – diapsids and synapsids appear
End of this period huge extinction took place (loss of 90% of species)
Reason is unknown – possible cooling took place. (meteor atmosphere?)
Large amount of earth surface change

18. Mesozoic Era Three parts Triassic, Jurassic and Cretaceous.
Known as the age of reptiles
Dinosaurs are found in these layers of rock
First birds are found in the Jurassic period
End of Cretaceous (66 milion years agao) a large extinction took place
A layer of iridium indicates a possible meteor hit or volcano’s erupted
Effects – nuclear winter, thick dust blocking out sun – cooler temp
Break up of land masses occurred

20. Cenozoic Two periods – tertiary and quaternary
Known as the age of mammals
Due to the extinction, animal competition was diminished and those that survived –thrived and differentiated.
Climate cooled and an ice age started that continues today.
Humans show up in this era