Chapter 16: Fossil Evidence For Evolution

Question 1

• Define ‘fossil’ and what they are used for.
• Define artefacts
• What do you understand by the terms ‘relative dating’ and ‘absolute dating’?
• Describe how Potassium-argon technique works to date rocks.
• Describe how radiocarbon dating works to date fossils.

Answer 1

• Any preserved trace left by an organism that lived long ago, to allow scientists to determine what extinct species were like.
• Objects that have been deliberately made by humans.
• Relative dating = comparison of age relative to something eles. Whereas absolute dating = actual age of material in years.
• Absolute dating technique based on decay of radioactive potassium-40 to form calcium-40 then argon-40. This occurs at a slow constant pace, therefore determining the amount of the two in rocks enables the age of it to be calculated.
• Plants use CO2 in photosynthesis from atmosphere. 1/billion of these carbon atoms are carbon 14 which decays over time at a fixed rate, whereas the rest are carbon 12. When animals eats plants, the carbon atoms become part of it. When it dies, intake of carbon 14 ceases and continues to decay. The amount of carbon 14 atoms halves every 5730 years. By measuring the ratio of carbon 14 to carbon 12, the age of the animal being dead can be calculated.

Question 2

• What are the advantages and limitations of carbon-14 dating?
• What are the advantages and limitations of potassium-argon dating method?
• Explain how dendrochronology is used as absolute dating for trees.
• What are the advantages and limitations of dendrochronology?
• For the following absolute dating methods, name the material used and the useful time range: tree growth rings, carbon-14 and potassium-argon.
• What is stratigraphy?
• What is the principle of superposition?
• Explain why the fossil record is important in providing evidence for evolution.

Answer 2

• Ad: Gives precise dates, used for recent fossils and artefacts given they are organic. Lim: up to 70 000 years, must contain carbon and carbon 14 in atmosphere varies.
• Ad: Gives precise dates. Lim: rocks between 100 000 to 200 000 years, and must have rock same age as fossil.
• Cross section of trees consist of rings, each representing a years growth. large width ring = favourable growing year and can be used as marker rings. A tree with a marker ring close to the centre, could be found near the outside of a cross section of another older tree. This method allows dating back thousands of years.
• Ad: Calculates absolute ages of fossil wood. Dis: timber rarely preserved, and useful for wood younger than 9000 years old.
• (wood and up to 9000years)(carbon compounds and up to 70000 years)(volcanic deposits and up to 100000 to 200000 years).
• Study of layers.
• A principle that assumes that in sedimentary rock layers, the layer at the top are younger than those beneath them.
• Fossil record establishes evolutionary links between species and provides evidence of which organisms lived on Earth in the past.

Question 3

• What is an index fossil? Could there be such things as index artefacts?
• Describe ways in which fossil pollen grains can be of use to the anthropologist.
• Describe fluorine dating
• What are phylogenetic trees and why are they used?
• What four conditions are required for formation of fossils?
• Why are there problems with the fossil record?
• Give examples of five different forms of fossils?
• What soil types are best for the preservation of fossils?
• Why is relative dating used when a number of good methods of absolute dating are available?

Answer 3

• Fossils from organisms that were widely distributed geographically, and were on Earth for a short period of time, and used relative dating. Yes as index artefacts can be indications of a particular culture at a particular time.
• Used as index fossils, to construct a pic of the vegetation around the time that the pollen was produced by plants and as an indicator of the climate conditions at the time the plants were living.
• A relative dating technique. Bones in soil are replaced by fluoride ions present in water in soil. Older fossil = more fluoride it contains.
• A diagram representation of evolutionary relationships between groups of organisms derived from a common ancestor.
  1. Quick burial 2.Presence of hard body parts 3.Absence of decay organisms 4.Long period of stability.
• Conditions for fossilisation do not always occur, fossils haven’t been discovered and destroyed by human activity.
• Footprints, bones, teeth, shells and petrified faeces.
• Alkaline soil
• Absolute dating has limitations that require certain conditions

Question 4

• What is the advantage and limitations of Accelerator mass spectrometry radio-carbon dating?
• Explain the principle behind radioisotope methods of dating.
• Describe why potassium-argon dating cannot be used to date fossil bones?
• Explain how AMS radiocarbon dating works.
• Does the principle of superposition always apply? If not, explain why.
• Describe the conditions that must be present to allow preservation of tissue. In these conditions, would you expect the bones of the body to be preserved?

Answer 4

• Ad: 100 micrograms samples, recent fossils and organic artefacts. Dis: up to 70 000 years, carbon-14 in atmosphere varies and must contain carbon.
• Radioisotope dating is based on the half-life of the radioactive isotope which decays at a known rate. Knowing how much radioactive product is in the fossil and its rate of decay allows the age of fossil to be calculated.
• The isotope is found in rocks of volcanic origin. Any bones trapped in volcanic rock would be destroyed by the heat.
• Sample is broken up into different types of atoms that it contains. The number of atoms of each isotope of carbon can then be counted.
• No, the layers can be shifted around by earth movements. The earth’s crust can fault and fold. Animals can bury artefacts into deeper soil layers. Human activity may result in fossils being found in sediments older than the fossil.
• Wet acidic soils with no oxygen. Bones wouldn’t be preserved as the acid would dissolve the calcium phosphate of the bones.

Question 5

-Explain why it is difficult to locate fossil specimens.

Answer 5

-Fossils may have been destroyed by human activity, might not be looking in the right places, buried too deep and fossils may have been destroyed by erosion.