1. CHAPTER 8 GEOLOGIC TIME

3. FOSSILS Preserved remains or traces of living things
Form when something dies and is covered by sediment that hardens into rock (Sedimentary Rock)
Usually are hard parts of an organism – teeth, bones, shells, seeds, woody stems

4. Types of Fossils
Molds – hollow area in sediment in the shape of the organism
Cast – a solid copy of the shape of the organism
Petrified fossils – “turned into stone”, minerals replace all parts of an organism
Carbon film – thin coating of carbon on a rock,
Trace Fossils – provide evidence of the activities of an organism, foot prints

8. Preserved Remains Little or no change to the organism Frozen remains
Amber – hardened resin or sap from trees
La Brea Tar Pits (CA) – animals were trapped in tar and died, tar soaked into their bones and preserved them

11. Change Over Time Paleontologist – study fossils
Use fossils to determine what past life forms were like
Classify organisms based on when they lived
Information collected makes up the fossil record
Fossil record provide evidence about past life and how life has changed. It also provides us evidence of past environments

12. Fossils and Past Environments
Fossils provide evidence of past climates
EX. Coal in Antarctica indicates that in the past it was much warmer
Fossils are used to learn about changes to Earth’s Surface
Ex. Fossils of past marine animals that are found in present day dry areas.

13. Fossils and Change Fossil record shows an order
gives evidence to the Theory of Evolution
Fossils record shows that many organisms have become EXTINCT – non longer exists

14. Relative Age of Rocks/ Fossils
Geologist have two ways to express the age of rocks/fossils:
Relative Age – age of rocks compared to the age of other rocks
Absolute Age – number of years since the rock formed

15. Position of Rock Layers
Absolute age can be hard to determine
Relative age can be determined using the LAW OF SUPERPOSITION:
In horizontal sedimentary rock, older layers are at the bottom and younger layers are closer to the top.

16. Determining Relative Age
Geologist study faults, igneous rocks and gaps in the geologic record to determine relative age.
Igneous Rock
Forms when lava or magma cools
Extrusion – lava that hardens on the surface
Younger than the rocks below it
Intrusion – magma that has pushed into bodies of rocks and cooled
Younger than the rock layers around and beneath it

17. FAULTS Break in the Earth’s crust
Rocks on opposite sides of faults move in different directions
Faults are younger than the rocks they cut through
Two types of faults:
Dip slip – two pieces of land change their vertical position compared to one another
Strike slip – two pieces of land move horizontally

18. Unconformity
Surface where new rock layers meet a much older rock surface beneath them
Occurs when some layers are eroded away, exposing older layers, then newer layers are deposited

20. Using Fossils to Date Rocks
Index fossil – fossils of widely distributed organisms that lived for a known, short time
EX. Ammonites
Since these animals only lived for a short time, their remains can be used to determine the age of the layer in which it was found

22. Absolute dating Also called Radiometric Dating
Puts an estimated number on the age of the rock layer
Performed on Igneous rocks
Cannot be performed on sedimentary rock
Made of pieces of different rocks

23. Half Life
Amount of time it take for half of the parent material to turn into (decay) daughter material.
Must know half life to determine age of rock or fossil

24. Molten rock cools
Inside rock is unstable radioactive atoms (parent atoms)
Unstable atoms decay to stable atoms (daughter atoms)
By comparing the amount of unstable atoms left to the amount of stable atoms, an estimate can be given about the age of the rock
Carbon 14 and Potassium/Argon dating are types of absolute dating

25. The Geologic Time Scale
Is a record of life forms and geologic events in Earth’s history
GTS is used because Earth’s time span is so long
Units used are called ERAS (long units of time) and periods
Ceno – recent
Meso – middle
Paleo – ancient or early
-zoic -- life

26. Major changes in life forms are used to mark a new unit geologic time
Precambrian Era – 88 percent of Earth’s history
Major Events
Formation of:
Sun and light
Earth (4.6 bya)
Atmosphere (from volcanic gasses)
Oceans (water vapor condensing)
life

27. Paleozoic Era
Began with early invertebrates (no backbone)– arachnids, insects
Then came vertebrates (fish, amphibians)
First plants, then some seed plants
Mass extinction to end the ERA

28. Mesozoic Era Reptiles dominated (including dinos)
Small mammals and birds appeared
Flowering plants developed
Mass extinction ended the ERA

29. Cenozoic Era New mammals appeared Diversity of life increased
Flowering plants the most common
Human show up