Fossils Flashcards
What are fossils?
Preserved traces left by organisms that lived long ago.
What are 5 examples of fossils?
1) entire organisms
2) parts of organisms (e.g. teeth)
3) footprints
4) burrows
5) impressions of plants
What can fossils be used for?
To give scientific insight to the past
To establish a sequence of evolution for a specific species
How are fossils formed? Where do most fossils form?
1) Organism dies
2) Organism is quickly covered in sediment before being eaten or moved
3) Sediment builds up over time
4) Increasing pressure turns sediment into rock
Usually formed within lakes, oceans, rivers or near volcanoes
What effect does wet, acidic soil have on the formation of fossils?
Wet, acidic soils will often destroy an organism before it can become fossilised.
However, wet, acidic soils with no oxygen can produce complete preservation of soft tissue and bone (e.g. tollundmanden and ellingkvinden)
What are the two techniques used to determine the age of a fossil?
Relative dating
Absolute dating
What is relative dating? What is an example of relative dating?
The comparison of two fossils to determine which is older. Actual age is not given.
Stratigraphy - comparison of layers within sedimentary rock. Correlation of rock strata compares layers of rock to determine which areas are older. Two areas with similar fossils can be assumed to be the same age.
By the law of superposition, fossils above are younger than fossils below
What is relative dating? What is an example of relative dating?
The comparison of two fossils to determine which is older. Actual age is not given.
Stratigraphy - comparison of layers within sedimentary rock
By the law of superposition, fossils above are younger than fossils below
Correlation of rock strata compares layers of rock to determine which areas are older. Two areas with similar fossils can be assumed to be the same age.
What are index fossils?
Fossils of organisms which were on earth for a short amount of time.
Useful in relative dating.
What is absolute dating?
Method of fossil dating which gives the actual, “absolute” age of the fossil.
Utilises the breakdown of radioactive substances, which break down at a fixed rate.
What is the Potassium Argon method of absolute dating?
Used for dating volcanic rocks, works best on rocks over 200,000 years old
Isotope K40 is used. Unstable, breaks down to form Ar40.
K40 has a half-life of 1250 billion years.
Proportion of K40 to Ar40 is compared to determine the age of the rock
What is the radiocarbon method of absolute dating?
Used for dating organic fossils less than 60,000 years old.
Isotope C14 is used.
1 C14 atom to every 1 trillion C12 atoms. Same proportion is absorbed into plants during photosynthesis, plants consumed by animals, after death C14 begins to decay at a constant rate.
Half-life of C14 is 5730 years.
C14 decays into N14. Ratio of C12 to C14 in a sample is measured to determine the fossil’s age.
What is tree ring dating?
Method used to date wood up to 9,000 years old.
Each concentric ring = 1 year of growth.
Wider ring = more favourable growing conditions that year.
Can be used to date structures build with wood (e.g. huts)
What are problems with the fossil record?
There are gaps in the fossil record, because:
1) It is rare for fossils to form
2) Fossils can be destroyed (geological events [earthquakes, erosion], human activity [site development, construction])
3) Fossils can be difficult to locate (may be buried too deep, too difficult to reach, digs occur in wrong places)
4) Limitations in fossil-dating methods
What is fluorine dating? Why can’t it be used for absolute dating?
Fluorine ions in soil water are absorbed, replacing ions in bone.
Higher concentration of fluoride = older fossil
Different areas have different concentrations of fluoride.
