Flashcards in Chapter 16 - Fossil Evidence For Evolution Deck (27):
What is a fossil?
Any preserved trace left by an organism that lived many years ago.
What are some examples of fossils?
What are 4 important factors required for fossils to form?
- a quick burial of the material
- the presence of hard body parts
- an absence of decay organisms (muscles etc)
- a long period of stability.
What happens if fossils are buried rapidly?
If buried rapidly, conditions may not be suitable for the activity of decay organisms and decomposition may be slowed or prevented.
- In wet, acid soils the minerals in the bone are dissolved and no fossilisation occurs.
- howevever if the soil has no oxygen (peat) fossilisation May occur. (Enzymes cannot work without oxygen).
Why are alkaline soils important?
- the minerals in the bones are not dissolved.
- new minerals, often lime or iron dioxide are deposited into the pores of the bone, replacing the organic matter.
What happens when a bone becomes petrified?
The bone is turned into rock.
Where are fossils of human ancestors usually found?
At the edges of ancient lakes, river systems, caves and volcanically active areas.
Lakes and rivers because they build up sediments when flooding occurs or water flows rapidly.
Many caves are in limestone (which consist of calcium and carbonate) which can be deposited around dead organisms.
In volcanic areas, ash can fall around the organisms of many human ancestors.
How are surface discoveries normally found?
Erosion, movement of soil via wind, floods etc, archeology, earth quakes, agriculture.
What are artefacts?
Artefacts are objects that have deliberately been made by humans.
What are some examples of artefacts?
Artefacts include stone tools, beads, carvings, charcoal from cooking fires and cave paintings.
Describe the process of discovering fossils.
1. Surveyed and marked.
2. Small hand tools
5. Labelled and catalogued
6. Scraped clean
7. Pieced, measured, moulded.
What is “dating”?
Dating is the excavation of fossils or artefacts to determine the age of the material.
What is the difference between absolute dates and relative dates?
Absolute dates provide the actual age of a specimen in years.
Relative dates tell us when one sample is older or younger than another.
Why is knowing the age of fossils important?
It helps scientists find the sequence of changes that have resulted in present day humans.
What does BP stand for?
BP stands for ‘before present’.
The age (or date) of a fossilisation usually given in years before the present time.
What are 3 examples of absolute dating?
- the potassium-argon technique
- the carbon-14 or radiocarbon dating method
- dendrochronology or tree ring dating
Describe the potassium argon technique.
And what is 1 negative of this technique?
- based on the decay of radioactive potassium to form calcium and argon.
- The isotope potassium-40 is radioactive and decays to form calcium-40 and argon-40. Such a decay takes place at an extremely slow but constant rate.
- determining the amounts of potassium-40 and argon-40 in a rock sample enables the age of the rock to be calculated.
- some suitable rock of the same age as the fossil must be available (rocks produced in volcanic eruptions)
What are isotopes?
Isotopes are different forms of an element, with different number of neurones in the nucleus of their atoms.
Describe the carbon-14 dating method.
And what are 3 negatives of this technique?
- Based on the decay of radioactive carbon-14 to nitrogen.
- plants use atmospheric carbon dioxide in photosynthesis and in one atom of every million million of carbon in plant tissue is carbon-14.animals eat, animals die, carbon decays at same rate.
- Over the period of 5730 years +- 40 years, half of any given quantity of carbon -14 breaks down. This is known as the half life of radioactive carbon.
- the normal method requires at least 3 grams of organic material.
- the material needs to contain organic compounds -carbon
- this technique must be treated with caution
What is accelerator mass spectrometry radio carbon dating?
A refined form of radiocarbon dating.
- only requires 100 micrograms of material.
- involved breaking the sample up into its constituent atoms so the number of atoms of each isotope of carbon can be counted.
Describe the tree-ring dating method.
And what is one negative of this technique?
- each concentric ring on the surface of a cut tree trunk represents one years growth and the rings differ in width according to how favourable the growing season was.
- it is possible to use wood from these trees for radiocarbon analysis.
- The particular conditions necessary for the use of this method do not occur often and timber is rarely preserved for more than a few thousand years.
For how many years BP can the three absolute dating methods be used for?
- Potassium-argon technique : 200 000 and earlier
- Carbon-14 : up to 60 000
- Tree growth rings : up to 9000
What are two examples of relative dating?
- Fluorine dating
Describe the stratigraphy technique
- the study of layers, or strata.
There are two main ways it can be useful ;
1. The principle of super position, which assumes that in layers of sedimentary rock the layers at the top are younger than those beneath them.
2. The correlation of rock strata, which is matching layers of rock from different areas.
- can be done by examining the rock itself and the fossils it contains. Rocks containing the same fossils may be assumed to be the same age. Such fossils are known at index fossils.
Describe flouring dating
- all the fossil bones in a particular deposit should contain the same amount of fluoride and so fossils that have been displaced can be detected.
- the older the fossil, the more fluoride in contains.
Why are there gaps in the fossil record?
- Some fossils haven’t been discovered.
- some are buried too deep underground or are in inaccessible places.
- some have been destroyed by agriculture or industry.
- some are incomplete.
- not all conditions produce fossils of organism’s remains.