Mechanisms and Evidence for Evolution Flashcards
what is Absolute Dating
finds the actual age
Absolute Dating:Potassium-Argon Dating
Measures the rate of radioactive potassium decay to form calcium and argon
Half-Life:
the time it takes for the radioactive elements to decompose by half.
what are the types of relive dating
Stratigraphy, Fluorine Dating
explain the 2 types of stratigraphy
Stratigraphy: study of layers or strata. They use two principles to do this…..
Principle of superposition (layer on top are young than the ones below)
Correlation of rock strata (matching layers of rocks from different layers).
Use of Index Fossils - fossils that allow for more precise relative dating, are known as index fossils
Index fossils are fossils which are used to define and identify geological time periods.
Were only in existence for specific time but were widespread.
Located at site, provide information about age of site.
EG. Fossilised pollen grains has developed into an important branch of science. They are useful as index fossils
explain fluorine relative dating
Fluorine relative dating:
When a bone in left in the soil, fluoride ions, which are present in water in the soil, replace some of the ions in the bones.
So, the older the fossil the more fluoride.
what are the limitations of Florine dating
Limitations
Fluoride ion levels in water differs from area to area.
Can only compare fossils from the SAME location.
what is the difference between fossil and an artefact
Fossil: the remains or impression of a prehistoric plant or animal embedded in rock or preserved in petrified form.
Artefact: an object made by a human being, typically one of cultural or historical interest. I.e. Tools or weapons
what are the conditions that fossilisation should occur
Conditions Away from- PREDATORS HEAT ELEMENTS (WIND, RAIN etc.) OXYGEN
Nature of the Soil
Wet, acidic soils- minerals in bone dissolve – NO FOSSILISATION
Wet, acidic soils, NO OXYGEN- preservation of soft tissues of animals as well as bones
Alkaline soils- bones preserved- produce best fossils.
Location of Fossils
Edges of ancient lakes and river systems, in caves or in volcanically active areas.
Quick burial- slows/prevents decomposition.
how are fossils discovered
Most fossils are discovered in the process of excavation.
The area to be investigated is first surveyed and marked out in sections.
Small hand tools are used to remove the soil gently so as not to damage any fossils or artefacts.
what are some problems with fossil records
Incomplete Fossilisation does not always occur Conditions may not be available Small portion of fossils have been discovered Buried too deep Inaccessible areas of the planet Destroyed by human activity Agriculture and industry Dating fossils can be problematic Time restraints Amount of samples obtained Type of sample being tested Unusual to find WHOLE organisms/ skeletons
what is fossil dating and what is the difference between absolute dating and relative dating
Determining the AGE of the materials
Various methods of dating fossils and materials associated with humans have been devised.
Some of these methods provide Absolute dating (the actual age) Relative dates (tells if one sample is older or younger then the other sample).
explain the 3 types of absolute dating
Potassium-Argon Dating
Measures the rate of radioactive potassium decay to form calcium and argon
Potassium 40 has a half-life of 1.3 billion years; measuring the amount of potassium 40 in rocks means that the age of rocks can be identified.
*Half-Life: the time it takes for the radioactive elements to decompose by half.
Carbon-14 (Radiocarbon)Dating
Living organisms are carbon-12 based. Carbon-12 is taken in through diet. A tiny portion of that carbon is Carbon-14 (radioactive). When an organism dies, it no longer takes in Carbon…no longer takes in Carbon-14. The C14 remaining in the body starts to break down- scientists can measure the amount of C14:C12 and provide an absolute date for how long the organism has been decaying for.
Dendrochronology
Tree ring dating is counting the concentric rings of the surface of a cut tree trunk.
Each ring = one year of growth
Difference in width = indicates how favourable the growing season was.
How?
Using a LIVING tree, it is possible to correlate marker rings with timber from ancient human structures
Work backwards to timber thousands of years old.
what are the limitations of Potassium-Argon Dating
Can only date VOLCANIC ROCKS
Older than 100 000- 200 000 years old
what are the limitations of Dendrochronology
Limited application
Timber is rarely preserved for more than a few thousand years
Also particular conditions necessary for the method do not occur often
what is relative dating
Does NOT determine the ACTUAL age of a fossil or artefact
DOES determine whether it is OLDER or YOUNGER than another sample or the rock or soil in which it was found.
