Chapter 11

Question 1

What is a fossil?

Answer 1

Any preserved trace left by an organism that lived long ago

Question 2

Fossil formation

Answer 2

1. Covered quickly to decrease bacteria (de-composers) and scavengers
   This could be: silt in river bed, volcanic ash, mudslides, resin (smaller organisms) or burial
2. Preservation of bone: soil has to be alkaline
   Preservation of soft tissue: soil has to be wet, acidic and low in oxygen

Question 3

Problems with the fossil record

Answer 3

Buried too deep
Destroyed by geological processes e.g sink back into mantle
Destroyed by human activity
Hard to identify (look like rocks)
Often located in politically unstable regions

Question 4

What is an index fossil?

Answer 4

Fossils or organisms that were on Earth for only a short period of time and therefore useful in the relative dating of rock strata.
Common
e.g some pollen grain fossils

Question 5

What is the principle of superposition?

One way in which stratigraphy can be useful in dating fossil material

Answer 5

Assumes that in layers of sedimentary rock the layers at the top are younger than material found lower down.

Question 6

What are absolute dates?

Answer 6

The actual age of the specimen

Question 7

What are relative dates?

Answer 7

A comparison of fossils to tell us whether one sample is older or younger than another.

Question 8

Potassium-argon dating

Absolute dating

Answer 8

Uses the decay of potassium-40 to form argon-40 and calcium-40. As the decay occurs at a constant rate, the proportion of potassium-40 and argon-40 in a rock allows the age of the specimen to be determined.
Used for rocks that are older than 200 000 years
Fossils can be dated by the age of near by rocks.

Question 9

Explain potassium-argon dating

Absolute dating technique

Answer 9

Uses the decay of potassium-40 to form argon-40 and calcium-40. As the decay occurs at a constant rate, the proportion of potassium-40 and argon-40 in a rock allows the age of the specimen to be determined.
Used for rocks that are older than 200 000 years
Fossils can be dated by the age of near by rocks.
As the rock ages, potassium-40 decreases whilst argon-40 increases.

Question 10

What is the half-life of potassium-40?

Answer 10

1250 billion years

Question 11

What is a half-life?

Answer 11

The time required for half of any quantity of radioactive material to decay into stable non-radioactive material.

Question 12

Explain carbon-14 dating/radiocarbon dating

Absolute dating technique

Answer 12

Uses the decay of of carbon-14 to form nitrogen. When organisms die, the carbon-14 that decays is not replaced as it is in living organisms. Therefore, the ratio of carbon-14 to carbon-12 can be used to calculate the age of the sample.
Useful for samples from living things that are less than 60 000 years old.

Question 13

How is carbon-14 formed?

Answer 13

Carbon-14 is produced in the upper atmosphere by the action of cosmic radiation on nitrogen at about the same rate at which it decays.

Question 14

What is the half-life of carbon-14?

Answer 14

5730 years

Question 15

What are the limitations of carbon-14 dating?

Answer 15

Cannot be used to date back more than 60 000 years
Material dated must contain organic compounds
The carbon-14 content of the atmosphere fluctuates

Question 16

What are the three areas of comparative anatomy?

Answer 16

Embryology, Homologous structures and Vestigial structures.

Question 17

What is Embryology?

Answer 17

Comparing the very early stages of the development of organisms. Similarities indicate a common ancestor.

Question 18

What are two features common to vertebrae embryos at one stage?

Answer 18

Gills slits and a tail.

Question 19

What are Homologous structures?

Answer 19

Structures that are similar in structure but may be used in different ways.
Organisms possessing homologous structures are likely to have a common ancestor.
E.g the forelimb in vertebrates

Question 20

What are Vestigial structures?

Answer 20

Structures that may once have been important but have lost or changed their function.
Some may retain lesser functions or develop new ones.
They are what remain of organs that were functional in ancestral forms and over time, and with changing environmental conditions, such organs were no longer essential to survival and gradually reduced.

Question 21

Give examples of Vestigial structures.

Answer 21

The nictitating membrane (third eyelid)
Third molars (wisdom teeth)
Humans still have the vertebrae for a tail, fused to form the coccyx.

Question 22

Explain the role of phylogenetic trees.

Answer 22

Shows the evolutionary relationship between species, with species with more recent common ancestors diverging further up the tree.
The ancestral organism forms the base of the tree.

Question 23

What is an isotope?

Answer 23

One of two or more atoms of the same element with the same atomic number and number of protons, but different number of neutrons.

Question 24

What is Accelerator mass spectrometry (AMS) radiocarbon dating?

Answer 24

A technique used to give radiocarbon dates for very small samples of material.