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Geologic Time and Paleontology. How Old is the Earth?. Lisa Herzog, Chief Preparator Paleontology and Geology Research Lab. Concepts to Understanding How Old the Earth is . Relative Time. - PowerPoint PPT Presentation
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Geologic Timeand Paleontology
How Old isthe Earth?
Lisa Herzog, Chief PreparatorPaleontology and Geology Research Lab
Concepts to UnderstandingHow Old the Earth is
Relative Aging Absolute AgingEstablishes events in the order that they occurred
A numeric age of a given sediment is calculated based on radiometric isotopes
Does not pinpoint an exact calendar age
Produces a numeric age, regardless of surrounding sediments/rock.
Only concerned with before or after
Measures amount of time lapsed
Must be measured in conjunction with surrounding sediments and fossils.
Can be determined in isolation, regardless of surrounding materials.
Relative Time Relative Geologic time has Four Main
Principles that refer to sedimentary strata, and a few others that further corroborate the conclusions of deep time.
One of the first main principles is….
UniformitarianismThe present is the key to the past
-James Hutton
The Principles ofRelative Geologic Time
Principle of original horizontality: Layers of sediment are deposited flat (horizontally)x
The Principles ofRelative Geologic Time
Principle of superposition: The older rocks are on the bottom
The Principles ofRelative Geologic Time
Principle of crosscutting relationships: Any rock that cuts through another MUST be younger.
The Principles ofRelative Geologic Time
Principle of included fragments: A Rock that includes fragments of other rock must be younger than the included fragments.
Relative Geologic Time & Fossils
Principle of faunal successionspecific fossils always appear in the samestratigraphic order in rocks.
Unconformitiesand Correlation
Disconformity – sedimentary layers parallel to each other
Angular unconformity – tilted layers with newer flat material atop
Nonconformity – sedimentary rocks atop igneous or metamorphic rock
Unconformitiesand Correlation Correlation – matching up rocks of similar age in different locales Index fossils – accurately indicates the age of a rock Key bed – a thin, widespread, synchronous sedimentary layer
Absolute Time
In Geology, Absolute Time should be thought of as ‘chronometric’ or ‘calendar’ dating. This is more accurate than the word ‘absolute’ as it inaccurately implies certainty and precision.
A numeric age of an event is calculated based on radiometric isotope dating. Absolute dating is the process of
determining an approximate computed age.
Chronometric Dating Measuring absolute age relies on:
Process that occurs at a constant rate Some cumulative record of that process
Isotopes – radioactive varieties of an element Vary by the number of neutrons
Half-life – the time it takes for one-half the atoms of a radioisotope to decompose to another isotope or element
Application to Rocks
Age of rock is determined by ratio of parent : daughter atoms The decay constant must be known
Determines whether half-life is short (min), or long (millions of years)
Rock can be accurately dated if fewer than four half-lives have passed (not enough parent atoms left to measure ratio)
Original rock should not have any daughter atoms present
Common Sources Carbon-14
Decays to nitrogen-14
Present in all living things from plants to animals
Half-life is approximately 5,000 years Can date fossils and
tissues up to 20,000 years old
Common Sources
Potassium-40 Decays to argon-40 and
Calcium-40 Present in igneous
minerals (apatite and muscovite)
Half-life is 1.3 billion years.
Most commonly used isotopes for radiometric dating
Thank YouPlease remember that no one single piece of evidence proves the time scale, or can definitively place an item/artifact in absolute historical position.
All of Geologic time and Paleontology is reliant on the interconnectedness of the data, the principles, and the overall evidence.
Lisa HerzogChief PreparatorPaleontology and Geology Research Laboratory