Fossil Formation and Stratigraphy

Question 1

What are requirements for fossilisation?

Answer 1

1. Material has to be set into rock to be considered a fossil (chemical changes e.g. mineralisation)
2. It must be buried or preserved for a sufficient amount of time (a period usually)
3. Water must always be present nearby, and must be covered in sediments fairly quickly

Question 2

What parts are fossilised in original part fossils?

Answer 2

• Original hard parts - bones, teeth, shells, eggs
• Original soft parts (more rare) - feathers, leaves, skin, soft bodied animals

Question 3

What are mold and cast fossils?

Answer 3

• Mold - negative or indent impression is left in the sediment
• Cast - mold fossils are filled in with minerals that harden over time, creating a fossilised replica of the original organism

Question 4

What are trace fossils (ichnofossils)?

Answer 4

Trace fossils or ichnofossils are imprints or other leftovers from an extinct organism, such as footprints, burrows, nests, chemical parkers and coprolites

Question 5

What is the significance of index fossils in generating a geological timescale?

Answer 5

• The boundaries between parts of the geological timescale can be identified by the fossils and rocks found
• The appearance and disappearance of index fossils or overlap of fossils in the strata define periods of the geological timescale. Specific types of characteristics within a species can help narrow down the time period (e.g. types of Trilobites)

Question 6

What is the Law of Original Horizontality?

Answer 6

The Law of Original Horizontality suggests that all rock layers are originally laid down (deposited) horizontally and can later be deformed

Question 7

What is the Law of Lateral Continuity?

Answer 7

The Law of Lateral Continuity suggests that all rock layers are laterally continuous and may be broken up or displaced by later events

Question 8

What is the Law of Superposition?

Answer 8

The Law of Superposition states that beds of rock on top are usually younger than those deposited below.

Question 9

What is the Priciple of Faunal Succession?

Answer 9

• The Principle of Faunal Succession states that a species appears, exists for a time, and then goes extinct.
• The observation that assemblages of fossil plants and animals follow or succeed each other in time in a predictable manner

Question 10

What is the Principle of Uniformitarianism?

Answer 10

The Principle of Uniformitarianism states that processes now visibly acting in the natural world are essentially the same as those that have acted throughout the history of the Earth, and are sufficient to account for all geologic phenomena.