Geologic Time Review

Geologic Time Review

by Schivonne John

Objectives - ​Discovering Earth's History

• ​Explain the principle of Uniformitarianism

• ​Describe how geologists use relative dating principles, inclusions and unconformities to help then understand Earth's history.

• Describe how geologists use correlation of rock layers to interpret the rock record.

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​Historical Notes ...

​Catastrophism

Landscape developed by catastrophes e.g. tornadoes, hurricanes, earthquakes, meteoritic impacts.

Modern geology

Uniformitarianism

Fundamental principle of geology

"The present is the key to the past." Meaning that to be able to determine the different types of geological processes that have occurred in the past, we can observe the geological processes that are occurring in the present.

Geological processes associated with uniformitarianism include weathering, erosion, continental drift, seafloor spreading.​

​

Multiple Choice

Identify the name of the belief system that supported the idea that Earth's landscapes were formed by a series of sudden, powerful events.

• Uniformitarianism

• Catastrophism

Multiple Choice

Identify the principle of modern geology that is underpinned by the statement "The Present is The Key to The Past."

• Catastrophism

• Uniformitarianism

Open Ended

What did James Hutton mean by his statement "The Present is The Key to The Past."

Open Ended

Identify 3 examples for what could be described as a catastrophic event.

Open Ended

Identify 3 examples of different types of geological processes for events that could be described as processes associated with uniformitarianism.

​Relative Dating

Placing rocks and events in sequence

Principles and rules of relative dating

Law of superposition – Oldest rocks are on the bottom

principle of original horizontality – sediment is deposited horizontally

principle of cross cutting relationships – younger feature cuts through an older feature

​Relative Dating

Principles and rules of Relative Dating

Inclusions – one rock contained within another (rock containing the inclusions is younger)

Unconformities

An unconformity is a break in the rock record

Types of unconformities

Angular unconformity – tilted rocks are overlain by flat-lying rocks

Disconformity – strata on either side are parallel

​Relative Dating

Principles and rules of Relative Dating

Unconformities: Types of unconformity

Nonconformity

Metamorphic or igneous rocks below

Younger sedimentary rocks above 

​Correlation of Rock Layers

​Matching rocks of similar age in different regions

Often relies upon fossils

Multiple Select

Identify the principles of relative dating

• Principle of Superposition

• Law of Original Horizontality

• Protrusions

• Principle of Cross-Cutting Relationships

• Unconformities

Multiple Choice

The law that states "in a column of rock, older samples are found further down than younger samples"

• Law of Cross-Cutting Relationships

• Law of Superposition

• Law of Horizontality

• Law of Absolute Dating

Open Ended

Identify the difference between an inclusion and a cross cutting relationship.

Open Ended

Define and identify the different types of unconformity (3)

​Fossils: Evidence of Past Life

fossils are the ​Remains or traces of prehistoric life   

Types of fossils

• Petrified – cavities and pores are filled with precipitated mineral matter

• Formed by replacement – cell material is removed and replaced with mineral matter

• Mold – shell or other structure is buried and then dissolved by underground water

• Cast – hollow space of a mold is filled with mineral matter

​Fossils: Evidence of Past Life

​Types of fossils

• Carbonization – organic matter becomes a thin residue of carbon

• Impression – replica of the fossil's surface preserved in fine-grained sediment

• Preservation in amber – hardened resin of ancient trees surrounds an organism

​Fossils: Evidence of Past Life

Types of fossils

Indirect evidence includes:

• Tracks

• Burrows

• Coprolites – fossil dung and stomach contents

• Gastroliths – stomach stones used to grind food by some extinct reptiles

​Fossils: Evidence of Past Life

Conditions favoring preservation

• Rapid burial

• Possession of hard parts

fossils and correlation

• Principle of fossil succession

• Fossils succeed one another in a definite and determinable order

• Proposed by William Smith – late 1700s and early 1800s   

​Fossils: Evidence of Past Life

Fossils and correlation

• Index fossils

• Widespread geographically

• Existed for a short range of geologic time

Multiple Choice

Which type of fossil is formed when water deposits minerals to fill in a space. This fossil has the exact same shape as the original organism?

• Petrified

• Imprint

• Cast

• Mold

Multiple Choice

What type of fossil is formed when mud fills in the hollow spaces around something hard, such as a shell, and then hardens. This results in a hollow space shaped exactly like the original object?

• Amber

• Mold

• Petrified

• Cast

Multiple Choice

This is a fossil in which minerals replace part or all of an organism. making it rock like.

• Imprint

• Cast

• Petrified

• Amber

Multiple Select

Select 2 answers. What does the fossil records tell us?

• Earth's History

• Changing Life Forms

• Age of Earth

Multiple Choice

The remains or traces of prehistoric life found in sediment and sedimentary rocks.

• Fossils

• Unaltered Remains

• Altered Remains

• Carbonization

Multiple Choice

A widespread geographically, are limited to a short span of geologicc time, and occur in large numbers.

• Index Fossils

• Fossils

• Fossil Succession

Multiple Choice

A fossil that shows the activity of organisms

• Index Fossil

• Cast and Mold

• Preserved Fossil

• Trace Fossil

Radioactivity and Radiometric Dating

Atomic structure reviewed 

• Nucleus 

• Protons – positively charged

• Neutrons - Neutral charge

• Protons and electrons combined

• Orbiting the nucleus are electrons – negative electrical charges

Radioactivity and Radiometric Dating

Atomic structure reviewed 

Atomic number

• An element's identifying number

• Number of protons in the atom's nucleus

Mass number

• Number of protons plus (added to) the number of neutrons in an atom's nucleus

Isotope

• Variant of the same parent atom

• Different number of neutrons and mass number

Radioactivity and Radiometric Dating

Radioactivity

• Spontaneous breaking apart (decay) of atomic nuclei

Radioactive decay

• Parent – an unstable isotope

• Daughter products – isotopes formed from the decay of a parent

Radioactivity and Radiometric Dating

Radioactivity

• Radioactive decay

Types of radioactive decay

• Alpha emission

• Beta emission

• Electron capture

Types Radioactive Decay

Radioactivity and Radiometric Dating

Radiometric dating

• Half-life – the time for one-half of the radioactive nuclei to decay

• Requires a closed system

• Cross-checks are used for accuracy

• Complex procedure

• Yields numerical dates

​The Radioactive Decay Curve

​Radioactivity and Radiometric Dating

Carbon-14 dating

• Half-life of only 5730 years

• Used to date very recent events

• Carbon-14 produced in upper atmosphere

• Incorporated into carbon dioxide

• Absorbed by living matter

• Useful tool for anthropologists, archeologists, historians, and geologists who study very recent Earth history

Multiple Choice

If a sample starts with 100 atoms of an unstable atom, how much will be left after 2 half-lives?

• 75

• 50

• 25

• 20

Multiple Choice

 

If there are 25 atoms left from a 100 atom sample of an isotope with a half life of 100 years, how old is the sample?

• 500 years

• 200 years

• 100 years

• 50 years

• 25 years

Multiple Choice

A radioactive element has a half-life of 2 days.

What percentage would remain radioactive after 6 days?

• 100%

• 75%

• 50%

• 25%

• 12.5%

Multiple Choice

A radioactive element has a half-life of 2 days. If the original mass was 120 grams, how much would have decayed after 6 days?

• 240 grams

• 120 grams

• 60 grams

• 30 grams

• 15 grams

Multiple Choice

A radioactive element has a half-life of 2 days. How many half-lives would it experience at 6 days?

• 5

• 4

• 3

• 2

• 1