Types of Fossilization

This article discusses the different types of fossilization, specifically focusing on casts. It explains how the type of fossilization can give us clues about the environment in which the fossil was formed. It also explores reasons why no fossils may be present in a sedimentary rock layer. Desklib provides study material and solved assignments on various subjects.

Activity 1: Types of Fossilization
1. What type of fossilization did you create in this lab?
Type of fossilization created in the laboratory was casts. The fossil mold was filled with
a paste and allowed to harden.
2. Why can the type of fossilization give us clues to the environment in which the fossil was
formed?
For the fossil to be formed and preserved, certain physical, chemical and biological
conditions must met. Fossil is formed if the organism has hard parts and was shielded
from destructive physical, chemical and biological conditions.
3. Imagine a sedimentary rock layer without fossils. Can you think of 3-4 reasons that could
explain why no fossils are present?
i) There was no creature(s) within its environment because of unbearable
environmental conditions for creatures to live.
ii) The sedimentary rock was formed under high-energy which could not allow
preservation of fossil. The fossil may have been pulverized or even carried away.
iii) The organisms living in that environment had soft bodies. This means that they
did not fossilize after death.
Activity 2: Biostratigraphy
1. Geologic age of the stratigraphic units
Layer 1: Hadean
Layer 2: Archean
Layer 3: Proterozoic
Layer 4: Phanerozoic
2. What is an index fossil and how is it used to identify stratigraphic units?
Index fossil is used to define and identify subdivisions of the geologic time scale. Index
fossil helps in identifying particular rock strata within layers presented in a column. This
allows geologists to identify rock units in the layers.
3. Name three factors that make a good index fossil.

i) Found in a wide geological range. This ensures that the range of ages of the strata
where the index fossil is situated is also small.
ii) Have definitive characteristics. This ensures that palaeontologists easily identifies
them.
iii) Do not easily decompose. Helps in prevention of the organism from becoming a
fossil.
Activity 3: Mass Extinction
1. In what layer is the extinction event located?
Cretaceous-Tertiary (K-T) extinction
2. What is the geologic age of the extinction event?
65 mya
3. What extinction event is represented in the exercise?
Dinosaurs, ammonites, most marine plankton, marine reptiles and many marine
vertebrates were wiped out.
4. What are possible causes of this extinction event?
i) Meteorite impact
ii) Tsunami.
iii) Molten quartz raining from the sky.
iv) Worldwide wild fires.
5. How are mass extinctions identified in the fossil record?
Mass extinction is identified by tracking the steady dying out of families of organisms at
a rate of 2 – 4.6 per million years and in some instances overlain by an upsurge in
extinction to around 10 to 20 families per million years.
6. How would you determine the difference between a local and global extinction event?
Local extinction covers a small geographical area such as a country. The data involved is
for a set area. Global extinction event involves extinction occurring on the whole planet
earth. The geographical area is equivalent to the size of the earth.
7. In a minimum of a paragraph, discuss what it would have been like during this extinction
event and what mechanisms may have helped creatures to survive.

During this extinction event, there is massive destruction occurring due to harsh
environmental conditions resulting to destruction of producers in food chain. This breaks
the food chain resulting to starvation and subsequent extinction of organism. Creatures
were able to survive if they were dependent on marine life for survival. Marine creatures
were less affected during this period.
Activity 4: Relative Dating
List the letters of the geologic units and features from oldest to youngest.
Using the principle of original horizontality as well as principle of superposition, the oldest layer
A is at the bottom and layer D is the topmost and the youngest.