Dating Techniques Flashcards
Describe the geological time scale?
- model used by geologist where geographical history is divided into units ( eras and periods)
-constructed by comparing similar fossils found in difference locations ( principle of superposition + bio stratigraphy correlation)
-> only intrestsed in a very small portion of Earths History ( Cainozoic- primates evolve)
-> fossil assigned area in time scale= given relative age( approx)
Analyse how to date fossils and its purpose
- Excavate-> date age of the fossil
purpose= gives an indication to the sequence of changes that have resulted in present day humans .
Describe the differences of Relative and Absolute dating.
Relative=> determines the age of the sample in comparision/relation to another and arranging them in geological order of their formation
Absolute dating=> determines the actual age of the specimen ( years) in historical order of their formation
=> date of fossil give in years before the present time
modern technology= more accurate estimations made on actual age of speciment which cannot be done using relative dating.
What are the relative dating limitations
- Qualitative
- less specific time( estimation) relative age
- Is very expensive and time consuming
- Works best on sedimentary rocks which have layered arrangement of sediment
What is stratigraphy and why is it useful?
The study of layers or strata
it is useful for dating fossil material using the principal of superposition the correlation of rock strata ( index fossils)
Top= young
bottom= Old
What is the relationship between strata and index fossils
Rocks that contain same index fossil considered to be the same age as fossil.
What are the limitations of stratigraphy.
Fossils/ artefacts could of been buried by animals/ humans may cause disposition of sediment
What are the key features of absolute dating techniques
~tell you the actual age of the sample
based any event which occurs at a constant rate
Finds age of rock/ sample using radiometric technique
Limitations
Qualitative
Very expensive and time consuming
works best for igenous. and metamorphic rocks
Describe radiometric dating
Uses radioactive or radioisotope
Determines the age of a rock/sample by measuring the proportions of original radioisotope and its decayed production
What are radioactive isotopes and what are the examples
an atom with the same atomic number but different amount of neutrons
Radioactive istopes are unstable and breakdown to form another more stable istope “
half life= the measurement of time taken for isotope to decay in half
carbon -14 -> nitrogen-14 ( 5730 years)
Potassium- 40-> argon -40 ( 1300 million years)
Describe carbon- nitrogen 14 dating
All living things absorb Carbon- 14, once dead no new Carbon-14 is absorbed-> thus carbon-14 decays to nitrogen 14 eventually
What are the limitations of carbon -14 dating
- Only works on living things/ organic
- 3g of organic sample is required
- Cannot date samples that are past 60,000 years old because not a lot of carbon-14 is left to be measured.
However can use Accelerator Mass Spec for smaller samples
Describe pottasium- Argon dating
The decaying of Potassium 40 to Argon-40 and Calcium-40
Used on rocks that have been heated to a very high temperature ( volcanic rocks)
. a nearby sample must be found
limitations of Pottasium- ARgon 40 dating
- the rock must be volcanic thus must be of a very high temperature
- Very expesnive and time consuming
- can only be used to measure samples that are 100,000-200,000 older this is because before this not enough decay has taken place
What is window period
There is a time frame limitations of both absolute dating techniques= a window period= when the rock/ sample cannot be dated (60000 to 200000)
