Index%20Fossils:%20Evolution%20and%20Biostratigraphy - PowerPoint PPT Presentation
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Index%20Fossils:%20Evolution%20and%20Biostratigraphy
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Title: Index%20Fossils:%20Evolution%20and%20Biostratigraphy
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Index Fossils Evolution and Biostratigraphy
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Evolution
- Variations exist within a population
- Result from mutations and other genetic accidents
- Some variations are advantageous
- Others are not
- Some are neutral
- Natural Selection works on these variations
- Characteristics of population shift through time
evolution
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What is Natural Selection?
- What phrase is commonly used to describe Natural
Selection? - Survival of the fittest
- What does it mean?
- Organisms best suited to the environment survive
long enough to reproduce. - Advantageous traits are passed on
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How do new species arise?
- When accumulated variations are great enough that
some individuals within the population cannot
interbreed, a new species has arisen. - New species commonly arise in geographically or
environmentally isolated areas. - New species and original species may exist at
same time
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Bio-Events
- First appearances of new species
- First appearances of new higher taxa
- Extinctions of species
- Mass extinctions of multiple taxa
- Bio-events are unique points in geologic time
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Index Fossils
- Some fossils are more useful than others for
relative age determinations - Fossils that are most useful are called INDEX
FOSSILS - What factors would maximize a fossils
usefulness? (i.e., What makes a good index
fossil?)
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What makes a good index fossil?
- Distinctive appearance/easy to recognize
- Short duration between first appearance and
extinction (a.k.a. RANGE) - Widespread geographic distribution (makes
correlation possible across a wide area/multiple
continents)
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Characteristics of Index Fossils
- Limited Stratigraphic Range
- Widespread Geographic Distribution
- Commonly Pelagic
- Or, tolerant of a wide variety of environments
(found in many facies)
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Mile Markers in Deep Time
- Life is unique for each interval of time because
of evolution and extinction - Volcanos, earthquakes, mountains, types of rocks
repeat throughout history - Life does not repeat it is directional
- Therefore, we can place other Earth events in a
framework based on fossils
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Mile Markers in Deep Time
- The fossil-based framework for Earth history is
known as the GEOLOGIC TIME SCALE - Units Eras, Periods, Epochs, Ages
- Boundaries between units are based on bio-events
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Index Fossils andInternational Stratotypes
- The Case of the Silurian Devonian Boundary
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Dr. Ivo Chlupác and Karlstejn
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Index Fossils and theSilurian - Devonian Boundary
- Graptolites
- Conodonts
- Chitinozoans
- Trilobites
- Brachiopods
- Cephalopods
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Definition ofthe S-D Boundary
- Stratotype Klonk, near Suchomasty, Czech
Republic
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S-D GSSP
- GSSP Global Stratotype, Sequence and Point
- First appearance of Monograptus uniformis
uniformis - Bed 20
- Klonk, Czechia
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Preserving the Stratotype
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