Chapter 8.4 Evidence for the Theory of Evolution: The Fossil Record

Question 1

Define paleontology

Answer 1

The study of fossils

Question 2

What can fossils tell us?

Answer 2

Shows clear change over time from simple to very complex organisms which is evidence for evolution

Question 3

What conditions are necessary for fossilisation to begin?

Answer 3

Organic matter must be quickly buried in sediments in an oxygen-poor environment to prevent decomposition

Question 4

How does sediment help preserve plant and animal remains?

Answer 4

It protects remains from oxygen and scavengers, slowing decay and allowing fossilisation

Question 5

What is mineralisation in fossilisation?

Answer 5

It’s when minerals from sediment replace natural bone or shell, making the remains harder and more likely to fossilise

Question 6

What type of sedimentary materials help form fossils?

Answer 6

-Mud
-Slit
-Sand
-Clay
which are all often carried and deposited by rivers and streams

Question 7

In what type of rock are fossils most commonly found?

Answer 7

Sedimentary rock

Question 8

Why aren’t fossils found in volcanic rock?

Answer 8

Molten lava is about 1000°C, which burns any organic material

Question 9

Can fossils be found in volcanic ash?

Answer 9

Yes if the ash is part of sedimentary layers that eroded and buried the organism

Question 10

Why are fossils rare in metamorphic rock?

Answer 10

Because the heat and pressure usually destroy organic remains

Question 11

What kinds of remains are most commonly fossilised?

Answer 11

Hard parts like bones and shells, but delicate tissues can occasionally be preserved

Question 12

How are impressions or films of thin tissues formed in rocks?

Answer 12

When tissues like leaves or mussels leave a mark or thin film in sedimentary rock

Question 13

What other conditions, apart from mineralisation, can lead to fossilisation?

Answer 13

Freezing or dehydration

Question 14

How are plants fossilised?

Answer 14

Some tissues is replaced with dissolved salts, a process called petrification

Question 15

What is pretrification?

Answer 15

Replacement of original plant tissue with rock-forming mineral

Question 16

Define the principle of superposition

Answer 16

The principle states that the oldest rock layer is found in the deepest position, and each consecutive layer above it is relatively younger; it indicates the relative ages of the rock layers and the fossils within them.

Question 17

What does the position of a fossil in rock layers indicate about its age?

Answer 17

Fossils found in lower rock layers are older than those near the surface, unless folding has occured.

Question 18

Define stratum (plural strata)

Answer 18

The layers of rock in an area (profile); strata occur in order, with the oldest layer at the bottom

Question 19

Define absolute dating

Answer 19

The process of determining the age of rocks and the fossils they contain based on the physical or chemical properties of, materials in the rock

Question 20

Define gradualism

Answer 20

A theoretical model of evolution that proposes there has been a steady, slow divergence of lineages, irrespective of gaps in the fossil organisms

Question 21

Define punctuated equilibrium

Answer 21

A theory of evolution that proposes new organisms evolve quickly after a long period of no change, rather than evolving by gradual change

Question 22

What two techniques are used to estimate the dates of fossils?

Answer 22

Comparative dating and absolute dating

Question 23

Define comparative dating

Answer 23

The process of determining the age of rocks and their contained fossils relative to one another, allowing an estimation of ‘oldest to youngest’, without assigning an actual age.

Question 24

What are the three types of absolute dating?

Answer 24

-Radiometric dating (most common)
-Electron spin resonance
-Luminescence

Question 25

Define radiometric dating

Answer 25

Uses the known rates of decay of naturally occurring radioactive isotopes present in a rock or fossil to obtain an absolute date for its age

Question 26

What are the main steps involved in the process of fossilisation

Answer 26

1) Death of organism 2) Rapid burial: The remains are quickly buried by sediment (mud, sand, slit) protecting them from scavengers and slowing decomposing 3) Lack of oxygen 4) Sediment accumulation: Over time more sediment layers build up and compress the lower layers, forming a sedimentary rock 5) Mineralisation: Minerals from surrounding sediments seep into the remains. These minerals replace the organic material, hardening the structure into the rock. 6) Uplift and erosion: After million of years, geological forces may lift the rock layers. Erosion from wind or water can eventually expose the fossil at the surface

Question 27

Most of our knowledge of the evolution of sharks is based on the remains of fossilised shark teeth. Suggest why other fossilised body parts of sharks haven't been found in abundance.

Answer 27

-Because sharks have skeletons made of cartilage, not bone. -Cartilage is softer and less dense than bone so it decays much faster and doesn't fossilise easily. -Teeth on the other hand are made of hard mineralised tissues which means they are much more durable and have a higher chance of fossilising. -That's why teeth are commonly found, while the rest of the body is rarely preserved

Question 28

What are some alternative ways (other than fossils) to determine how closely related present-day animals are to each other?

Answer 28

-DNA/molecular comparisons -Comparative anatomy -Embryology -Biogeography -Behavioural and physiological traits

Question 29

Why is tracing the evolution of jellyfish through fossils difficult?

Answer 29

1) They are soft-bodied animals: Jellyfish don't have bones or shells, so they rarely leave behind fossils evidence 2) Rapid decay: Their bodies break down quickly, often before they can be buried in sediment 3) Unfavourable environment: They usually live and die in the open ocean, not in areas where fossilisation is likely 4) Poor fossil quality: When fossils do form, they're often faint or incomplete, making it hard to identify evolutionary traits

Question 30

What do isotopes of the same element have in common and what differs?

Answer 30

They have the same number of protons (same atomic number) but different numbers of neutrons (different atomic mass).

Question 31

What are the three natural isotopes of carbon?

Answer 31

-Carbon-12 -Carbon-13 -Carbon-14.

Question 32

How many protons and neutrons does carbon-12 have?

Answer 32

6 protons and 6 neutrons.

Question 33

How many protons and neutrons does carbon-14 have?

Answer 33

6 protons and 8 neutrons.

Question 34

What makes some isotopes radioactive?

Answer 34

They have unstable nuclei that emit energy as alpha, beta, or gamma rays.

Question 35

What is the half-life of an isotope?

Answer 35

The time it takes for half of the radioactive nuclei in a sample to decay.

Question 36

Into what does carbon-14 decay?

Answer 36

Nitrogen-14.

Question 37

What is the half-life of carbon-14?

Answer 37

5730 years.

Question 38

What does carbon dating compare to estimate age?

Answer 38

The percentage of carbon-14 remaining in a sample compared to atmospheric carbon-14.

Question 39

Why is the result of carbon dating often given as ±x years?

Answer 39

Because atmospheric carbon-14 levels vary over time, as shown by tree ring data.

Question 40

What is the maximum reliable age range for carbon-14 dating?

Answer 40

Up to about 12,000 years.

Question 41

Why is carbon-14 dating unreliable for samples older than 12,000 years?

Answer 41

The carbon-14 levels become too low to measure accurately.

Question 42

What radioactive isotope is often used for dating older samples?

Answer 42

Potassium-40, which decays into argon.

Question 43

Why is carbon-14 not usually used to date fossils, and how can their age still be estimated?

Answer 43

Carbon-14 is not usually used because fossils are often mineralised with their original carbon-containing tissues replaced or altered, and fossilisation generally takes longer than the 12,000-year limit of carbon-14 dating. Instead, scientists determine the radioactive isotopes present in the sample to estimate the fossil's age.

Question 44

How can the age of a fossil still be estimated if carbon-14 dating isn’t suitable?

Answer 44

By determining the radioactive isotopes present in the sample and calculating based on their decay.