Chapter 11 Flashcards
What is a fossil?
Any preserved trace left by an organism that lived long ago
Fossil formation
- Covered quickly to decrease bacteria (de-composers) and scavengers
This could be: silt in river bed, volcanic ash, mudslides, resin (smaller organisms) or burial - Preservation of bone: soil has to be alkaline
Preservation of soft tissue: soil has to be wet, acidic and low in oxygen
Problems with the fossil record
Buried too deep
Destroyed by geological processes e.g sink back into mantle
Destroyed by human activity
Hard to identify (look like rocks)
Often located in politically unstable regions
What is an index fossil?
Fossils or organisms that were on Earth for only a short period of time and therefore useful in the relative dating of rock strata.
Common
e.g some pollen grain fossils
What is the principle of superposition?
One way in which stratigraphy can be useful in dating fossil material
Assumes that in layers of sedimentary rock the layers at the top are younger than material found lower down.
What are absolute dates?
The actual age of the specimen
What are relative dates?
A comparison of fossils to tell us whether one sample is older or younger than another.
Potassium-argon dating
Absolute dating
Uses the decay of potassium-40 to form argon-40 and calcium-40. As the decay occurs at a constant rate, the proportion of potassium-40 and argon-40 in a rock allows the age of the specimen to be determined.
Used for rocks that are older than 200 000 years
Fossils can be dated by the age of near by rocks.
Explain potassium-argon dating
Absolute dating technique
Uses the decay of potassium-40 to form argon-40 and calcium-40. As the decay occurs at a constant rate, the proportion of potassium-40 and argon-40 in a rock allows the age of the specimen to be determined.
Used for rocks that are older than 200 000 years
Fossils can be dated by the age of near by rocks.
As the rock ages, potassium-40 decreases whilst argon-40 increases.
What is the half-life of potassium-40?
1250 billion years
What is a half-life?
The time required for half of any quantity of radioactive material to decay into stable non-radioactive material.
Explain carbon-14 dating/radiocarbon dating
Absolute dating technique
Uses the decay of of carbon-14 to form nitrogen. When organisms die, the carbon-14 that decays is not replaced as it is in living organisms. Therefore, the ratio of carbon-14 to carbon-12 can be used to calculate the age of the sample.
Useful for samples from living things that are less than 60 000 years old.
How is carbon-14 formed?
Carbon-14 is produced in the upper atmosphere by the action of cosmic radiation on nitrogen at about the same rate at which it decays.
What is the half-life of carbon-14?
5730 years
What are the limitations of carbon-14 dating?
Cannot be used to date back more than 60 000 years
Material dated must contain organic compounds
The carbon-14 content of the atmosphere fluctuates
What are the three areas of comparative anatomy?
Embryology, Homologous structures and Vestigial structures.
What is Embryology?
Comparing the very early stages of the development of organisms. Similarities indicate a common ancestor.
What are two features common to vertebrae embryos at one stage?
Gills slits and a tail.
What are Homologous structures?
Structures that are similar in structure but may be used in different ways.
Organisms possessing homologous structures are likely to have a common ancestor.
E.g the forelimb in vertebrates
What are Vestigial structures?
Structures that may once have been important but have lost or changed their function.
Some may retain lesser functions or develop new ones.
They are what remain of organs that were functional in ancestral forms and over time, and with changing environmental conditions, such organs were no longer essential to survival and gradually reduced.
Give examples of Vestigial structures.
The nictitating membrane (third eyelid)
Third molars (wisdom teeth)
Humans still have the vertebrae for a tail, fused to form the coccyx.
Explain the role of phylogenetic trees.
Shows the evolutionary relationship between species, with species with more recent common ancestors diverging further up the tree.
The ancestral organism forms the base of the tree.
What is an isotope?
One of two or more atoms of the same element with the same atomic number and number of protons, but different number of neutrons.
What is Accelerator mass spectrometry (AMS) radiocarbon dating?
A technique used to give radiocarbon dates for very small samples of material.
