Chapter 11 Flashcards
study
Fossil
Any preserved trace left by an organism that lived long ago
Effect of soil type on fossilisation
Wet acidic soils= no preservartion (unless no oxygen is present)
Alakline soil= best fossils are formed as no minerals in the bone are dissolved.
Location of fossils
Human fossils are found at the edge of lakes rivers, cave systems or volcanic areas as these conditions cause immediate burial to occur
How are fossils discovered
Through erosion or a slow excavation process
What conditions allow for preservation
Alkaline soils, no oxygen, limestone caves ‘
Nearby lakes and river systems
Quick burial
Dating
Determining the age of the fossil or material
Absolute dating
The actual age of specimen in years
Relative dating
A comparison of fossils to tell us whether one sample is older or younger than another
Potassium argon dating
The dating technique based on the decay or radioactive potassium to form calcium and argon
Potassium 40
A radioactive isotope of potassium containing 21 neutrons that decays at a constant slow rate to form calcium 40 and argon 40.
Carbon 14 dating
Dating technique based on the decay of the radioactive isotope carbon 14 to nitrogen
Carbon 12 to Carbon 14 ratio
1:10^12
Half life of carbon 14
5730 +/- 40
Half life of potassium 40
1250 billion years
AMS and what does it involve
Accelerator mass spectrometry
-Involves breaking up the sample into singular atoms - so that the number of atoms in each isotope can be counted
What does carbon 14 dating require
Sample must be younger than 60,000 years
Material must contain organic compounds
At least 3 grams of organic compounds (for the “normal” method withous AMS)
Stratigraphy
The study of layers- strata
Principle of superposition
Assumes that the layers above are younger than those beneath them
-Must be applied with caution as crust can be distorte due to tectonic activity or human/animal burials/activities
Correlation of rock strata
Involves matching rock strata from different areas- as rocks that contain the same fossil may be assumed to be the same age.
Index fossils
fossils that are widely distirvuted but only occured during a limited time period
-Helpful to compare rock strata and allow relative dating to e more precise
Problems with fossil record
Very incomplete as conditions do not always occur or occur at irregular periods of time
4 necessary conditions
-Quick burial
-Absence of decay organisms
-Long period stability
-Presence of hard body parts
Phylogenetic trees
A diagram that represents the evolutionary relationship between a number of organisms derived from a common ancestor
