Transcript Chapter 12

Chapter 12
Clues to Earth’s Past
12.1 Fossils
1. What can fossils tell us?
- Where, when, and how organisms
lived
2. 2 most important conditions
necessary for an organism to
become a fossil:
1. To be buried quickly
2. Have hard parts
3. How an organism’s remains petrified:
- Some or all of the original
materials in the remains have been
replaced by minerals.
4. How an organism’s remains can
become carbonaceous film:
- The organism is buried by
sediments which pile up increasing
the heat and pressure. Gases and
liquids are forced from body, thin
film of carbon residue is left
forming an outline.
Petrified Log
Trilobite
5. Process of fossilization as an organism is buried,
becomes a mold, then a cast:
A. The fossil begins to weather and erode
as water moves through pores in rock
layers.
B. The fossil is eroded away, the harder
rock surrounding it forms a mold.
C. Sediments are carried into the mold and
deposited.
D. A cast is formed.
6. Three ways that the original
remains are preserved:
1. Frozen in ground
2. Trapped in amber
3. Trapped in tar
crustacean burrows -middle Jurassic
coprolite (dino poo)
7. Four types of information that trace
fossils can tell about animals:
1.
Size, weight, age
2.
Speed animal was traveling
3.
Lifestyle of animal
4.
Social life of animal
8. What do scientists use index fossils
for?
- To date rock layers
12.3 Relative Age of Rocks
1.
What does the principle of superposition state?
-
In a sequence of sedimentary rock layers,
the oldest layer is on the bottom, the
youngest on the top.
2. How are sediments deposited?
- In horizontal layers
3. What is relative dating?
- Determining the order of events or relative
ages of rocks by their position in sequence.
4. What is unconformity?
- A gap in the sequence.
* Develops when sedimentary rock
layers are uplifted, tilted and/or
eroded away.
Angular Unconformity
 Horizontal
layers are uplifted, tilted,
and eroded, then more layers are
deposited horizontally.
Disconformity
 Layers
are deposited, uplifted, and
eroded, more layers are deposited
horizontally.
Nonconformity
 Sedimentary
layers are deposited on
top of igneous or metamorphic rocks.