Chapter 11 - Other evidence of evolution

Question 1

fossil

Answer 1

any preserved trace left left by an organism that lived long ago. eg, bones, shells, teeth, footprints

Question 2

what do fossils and the rock in which they are found tell us

Answer 2

what the organisms ate, what other organisms existed at that time and what the climate was like

Question 3

How are fossils formed

Answer 3

Part of organisms may become fossilised when buried by drifting sand, mud deposited by rivers, volcanic ash or other members of the same species. If buried rapidly, conditions may not be suitable for decomposers and decomposition may be slowed or prevented

Question 4

which soil doesn’t allow for fossil formation

Answer 4

And wet, acidic soils the minerals in the bone are dissolved and no fossilisation occurs, except if the soil contains no oxygen

Question 5

which soils produce the best fossils

Answer 5

Bones buried and alkaline soils because the minerals in the bones are not dissolved

Question 6

Why are fossils often found near lakes and rivers

Answer 6

Because the organism can be buried rapidly, preventing decomposition. Lakes and rivers build up sediments when flooding occurs or when the water flow slows rapidly

Question 7

what are artefacts

Answer 7

Objects that have been deliberately made by humans. E.g. stone tools, beads, carvings

Question 8

Absolute dates

Answer 8

The actual age (in years) of a fossil or artefact

Question 9

relative dates

Answer 9

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

Question 10

Potassium argon dating

Answer 10

A method of calculating the age of a fossil or artefact using the known rate of decay of radioactive potassium.

Question 11

how does potassium argon dating work

Answer 11

Potassium-40 is a radioactive isotope and decays to form calcium-40 and Argon-40. Such decay takes place at an extremely slow but constant rate and so determining the amounts of potassium-40 and argon-40 in a rock sample enables the age of the rock to be calculated. As the rock ages, the portion of potassium-40 in decreases while that of argon-40 increases.

Question 12

what are the limitations of potassium argon dating

Answer 12

not all rock types are suitable for this method of dating and it can only date rocks older than 100,000 to 200,000 years as after 100,000 years only 0.0053% of the potassium-40 has decayed and such small amounts are hard to detect

Question 13

what is half life and what is the half life of potassium-40

Answer 13

The time required for half of any quantity of radioactive material to decay into stable non radioactive material. The half life of potassium-40 is 1250 billion years (1.25 x 10^9 years)

Question 14

When is potassium argon dating most useful

Answer 14

On samples that are older than 200 000 years

Question 15

Isotopes

Answer 15

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

Question 16

Carbon-14

Answer 16

The radioactive isotope of carbon

Question 17

Radiocarbon dating

Answer 17

The calculation of the age of a fossil or artefact using the rate of decay of radioactive carbon to nitrogen

Question 18

Explain carbon-14 dating

Answer 18

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. When green plants use atmospheric carbon dioxide in photosynthesis, one in every million carbon atoms is carbon -14. If an animal eats the plant, the carbon-14 becomes a part of the animals tissues. With death, intake of carbon-14 ceases, but the carbon-14 already in the tissues continues to decay at a fixed rate. By measuring the amount of radiation liberated by a sample, the ratio of carbon-14 to carbon-12 can be estimated and an age calculated

Question 19

what is the half life of carbon-14

Answer 19

5730 ± 40 years

Question 20

what is AMS radiocarbon dating

Answer 20

Accelerator Mass Spectrometry is a technique used to give radiocarbon dates for very small samples of material (100 micrograms). Involves breaking up the sample into its constituent atoms so that the number of atoms of each isotope of carbon can be counted

Question 21

what are the limitations of radiocarbon dating

Answer 21

• Can only be used up to 60000 years ago
• Material to be dated must contain organic compounds
• Amount of carbon-14 in the atmosphere varies, was thought to be constant

Question 22

Stratigraphy

Answer 22

The study of the sequence of rock layers as a means of relative dating

Question 23

what are the two ways in which stratigraphy can be useful in dating fossil material

Answer 23

Principle of superposition and Correlation of rock strata

Question 24

Principle of superposition

Answer 24

In a vertical sequence, the principle that the sedimentary rock layers on top will be younger than those lower down

Question 25

Correlation of rock strata

Answer 25

The process of matching rock strata from different places

Question 26

Index fossils

Answer 26

Fossils or organisms that were on Earth for only a short period of time and therefore useful in the relative dating of rock strata

Question 27

problems with the principle of superposition

Answer 27

- Distortion of Earth's crust do occur and a sequence of rock layers may be turned upside down - Fossils or artefacts may be buried by animals or humans, in this case the specimen may be younger than some of the layers above it

Question 28

what are the four conditions that are required for fossils to be formed

Answer 28

- Quick burial of the material - Presence of hard body parts - Absence of decay organisms - Long period of stability (organism needs to be left undisturbed)

Question 29

problems with the fossil record

Answer 29

Fossilisation is a chance occurrence and there are many gaps in the fossil record because organisms have not been preserved and only a very small proportion of the fossils that do exist have actually been discovered, some are buried too deep or are inaccessible. Others may have been destroyed by human activity or not recognised as fossils

Question 30

Embryology

Answer 30

The study of early development of an organism.

Question 31

Homologous structures

Answer 31

Structures with a similar structure but not necessarily a similar function. Eg, Feet of amphibians and reptiles, wings of bats and birds, leg of hose, flipper of whale, human hand

Question 32

Vestigial structures

Answer 32

A structure of reduced size that appears to have no function.

Question 33

4 examples of vestigial structures

Answer 33

- Nictitating membrane - Ear muscles - Wisdom teeth - Appendix

Question 34

Phylogenetic tree

Answer 34

a diagram showing evolutionary relationships between related organisms, also called dendrogram