1. The Record of Time
Science Grade 8

2. What are Fossils?
Fossil – remains or evidence of once living organisms.
Most fossils are made from mineralized bones.
Process: Water dissolves in porous bones and become hard like a rock.
Most are hard body parts (petrified fossil)
They are frozen in soil or ice, dehydrated in caves, trapped in amber
Found mostly in sedimentary rock.
5 main types of fossils:

3. FIVE MAIN TYPES OF FOSSILS
Petrified
Fossils
Molds and
Casts
Carbon Films
Trace
Fossils
Preserved
Remains

4. How Reliable is the Fossil Record?
Fossil Record – made up of all fossils ever discovered. It provides evidence that species have changed over time.
Biased due to:
Search for fossils is unequal between continents.
Climate
Structures not being preserved the same way
It is important to be careful with assessing individual fossils.
Why should we assess a group of the same species instead of just an individual?
Some individuals may have illnesses or deformities that is not normal to their species.
Gaps in the fossil record
create “missing links”
chain in evolution
Shows changes among species over time

5. What Do The Fossils Tell Us?
Evolutionary processes (how species evolved over time)
Reconstruct body shapes
Through fossils we can determine:
Gender
Physical capabilities
Growth patterns
Life expectancy
Movement
Size/shape/position of organs
How humans and Earth have changed over time

6. Dating Techniques Types:
Relative dating – determination of the age of a rock or geologic event by comparing with other rocks/geologic events
Types:
The Law of Superposition
The Law of Original Horizontality
The Law of Cross Cutting Relationships
The Law of Lateral Continuity
The Law of Included Fragments
Date fossils based on the strata found (same strata = same timeframe)
Relative dating is not always accurate due to unconformities.
Unconformity – missing layers in the rock record due to erosion

7. Dating Techniques
Absolute Dating – the process of establishing the age of an object by determining the number of years it has existed.
Measured through
Radioactive decay
Biological clock (example: tree rings)

8. Index Fossils
Index fossils – a tool used to determine the relative age of rock layers.
Index fossils existed only during specific spans of time before becoming extinct.
If you use absolute dating to get an age for the fossil, then you know that the rock the fossil is found in is also that age.