Chapter 16

Question 1

Fossil

Answer 1

Any preserved trace left by an organism that lived long ago.
Examples: footprints, burrow, bones, shells and teeth.

Question 2

Artefact

Answer 2

Objects that have been deliberately made by humans.

Question 3

What is an index fossil?

Answer 3

Index fossils are fossils that only exist for a short period of time (appearing in one layer) that need to be widespread.

Example - pollen grains (determines type of vegetation), trilobites.

Question 4

What are the best soil types for preservation of fossils?

Answer 4

Absence of oxygen, dry, cold, salty and alkaline conditions (opposite of acidic, high pH)

Question 5

Relative dating?

Answer 5

Comparison between a fossil/artefact (can’t give age) -> no numbers.

Examples: stratigraphy, fluorine dating.

Question 6

Absolute dating?

Answer 6

The actual age of the fossil is given (in years).

Examples: carbon dating, potassium argon and dendrochronology.

Question 7

Why is relative dating used when absolute dating has good methods?

Answer 7

Absolute dating has limitations:

• Potassium-argon (Not all rocks suitable).
• Carbon-14 (Only useful for material up to 70,000 years old).
• Dendrochronology (Timber rarely preserved).

Question 8

Radioisotope = Carbon 14 and potassium argon dating,

What are it’s methods?

Answer 8

The principle is that atoms decay with a known half life.

Comparing the amount of carbon (5370 years - half life) or potassium that has decayed.

Question 9

Carbon 14 dating/lifecycle

Answer 9

Carbon 14 is unstable with a known half life.
It exists at a known ratio with carbon 14 that we keep up by continually eating plants/animals.
After death and fossilisation, we no longer maintain that ratio.
Carbon 14 decays without being replenished.

Question 10

What is a half life?

Answer 10

Length of time it takes for half the carbon to decay.

Question 11

AMS radiocarbon dating?

Answer 11

Can be used to date a sample as small as 100 micrograms.

Question 12

Dendrochronology?

Answer 12

Each ring of tree = year of growth.
Marker ring = weather conditions causing notably different rings.
Thicker rings = good year, vice versa
Once we know the year that a marker ring happened, we can use older, dead trees to figure out the year an older marker point happened.

Question 13

Does superposition always apply?

Answer 13

No because of digging and tectonic plate movement

Movement in the earths crust

Question 14

Explain how index fossils can be used to compare strata from different locations.

Answer 14

Because index fossils are widespread and occur for only short periods of time - you know that the strata came from the time of the index fossil and therefore you can relatively date the ones on either side.

Question 15

Usefulness of pollen grains

Answer 15

Index fossil
Type of environment
Food types (vegetation)

Question 16

Fluorine dating?

Answer 16

More fluorine it contains, the older the fossil
Some fossils maybe older than others and contain less fluorine, depending on the ground water (one can contain more fluorine)

Limitation: you can compare the two fossils if they’re from the same area

Question 17

Explain how Carbon-14 determines the age of fossil remains

Answer 17

Form of absolute dating - meaning it can give an exact age
Every 5730 years, that’s how long the fossil has been there for half its lifetime
Can be passed on in food chain, absorbed by plants which are ate by animals and we then consume animals

Question 18

Limitations of carbon-14 dating

Answer 18

Can only date once living things - cannot date rocks etc

Can only date up to 70,000 years old - will eventually be NO carbon left

Question 19

Phylogenetic trees

Answer 19

Shows where each animal has evolved from and showing how closely related we are to a particular species

Question 20

Limitations of potassium argon dating

Answer 20

Not all rocks suitable (rocks produced in volcanic eruptions)
Useful for rocks between 100,000-200,000 years or older
Must have rock same age as a fossil

Question 21

Carbon 14 limitations

Answer 21

70,000 or younger
Must contain carbon
Carbon varies in atmosphere
Requires 3 grams of carbon

Question 22

Dendrochronology limitations

Answer 22

Timber rarely preserved
Only can date 9,000 years or younger
Only useful for wood

Question 23

Potassium argon dating

Answer 23

Based on the decay of radioactive potassium to form - calcium and argon

Question 24

Correlation of rock strata

Answer 24

Matching the layers of rick from different areas to form a time scale

Question 25

Principle of superposition

Answer 25

Layers at the top are younger than those beneath them