Geologic History Note Packet

Unit 7: Geologic History Earth Science- Ms. Gill Note Packet #8

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UNIT 7: EARTH’S HISTORY

PACKET 8: EARLY EARTH, SEQUENCING EVENTS, RELATIVE AGE, ABSOLUTE AGE, FOSSIL RECORD

HONORS EARTH SCIENCE MS. GILL

NOTE PACKET #8

NAME:_______________________ PER:____ DATE:______ ________

“Maybe one day I’ll make a good index

fossil” P.S. I’m Boris


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Vocabulary: absolute dating Big Bang correlation cross-cutting relationships erosion evolution extinction extrusion faulting folding, fossil record half-life index fossil inclusion intrusion isotope meteoritic debris original horizontality Out-gassing radioactive decay red-shift (Doppler effect) relative dating rock record stratigraphy superposition unconformity Uniformitarianism volcanic ash layer


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Earth’s Formation •Earth formed through the gravitational _________________ and __________________ of asteroids and rocky debris. •This accretion of material generated a tremendous ______________ causing the planet to be molten. •The denser materials settled into the interior and the Earth’s _____________ internal structure formed. -Earth's first atmosphere 4.6 billion years ago was most likely comprised of hydrogen and helium (two most abundant gases found in the universe!)Through the process of outgassing, the outpouring of gases from the earth's interior, many other gases were injected into the atmosphere. These include:

water vapor (produced rain - rivers, lakes, oceans), carbon dioxide, nitrogen As outgassing occurred over a period of millions of years, the atmosphere evolved to its current state

Life and Evolution: Variations in Fossils and Environments •Evidence from the ______________________ (preserved in sedimentary rocks) shows that a wide variety of life forms have lived in Earth’s changing environments over time. •The comparisons of fossil remains and ______________________________ enable scientists to make predictions about the Earth’s past environment. •A major reason for changes in Earth’s _________________ over geologic time has been the movements of plates and their associated landmasses. Fossils and the Evolution of Life The theory of ______________________ states that life forms change through time. As environmental conditions change, variations within a species give certain individuals a greater chance for _________________ and __________________. Rates of Evolution The ________________________ provides evidence for the theory of organic evolution. This also shows that evolution does not always occur at the same _________. There are times of rapid ___________ and subsequently rapid ________________ of new species.

• An impact event, such as the collision of a comet or asteroid with Earth, may cause catastrophic environmental changes leading to rapid extinctions and evolutions.

• Such an event probable occurred at 65 million years ago and is associated with a massive extinction of roughly 70% of the Earth’s species.


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Life On Earth

Precambrian (4.6 - 4.06 b.y.) {Little to No Life} - Simple organisms (soft-bodied; “jellyfish”) - Fossils are rare Paleozoic (540 – 245 m.y.) {Life in the Oceans} - Organisms proliferate and become more complex (_______________________) - Shelled (mineralized skeletons and shells) organisms develop (Brachiopods/Trilobites) - _______________________ develop from lobe-finned fish - Era ends with a ________________________ killing off more than 95% of the life on earth Mesozoic Life (245-65) {Life on Land and Oceans, Dinosaurs!} - “Age of _________________” (dinosaurs, flying reptiles and birds develop) - Modern _____________________________ begins to develop on land - Era ends with a mass extinction killing off dinosaurs, ammonoids, flying reptiles, and some

swimming reptiles.

Cenozoic Life (65 m.y. – present) {Life on Land and Oceans} - “Age of Mammals” (____________ begin to develop and evolve) - Humans develop from _______________ (Homo Habilus 1.6 m.y.)

The study of Geologic History began in the late 1700’s when James Hutton published his Theory of the Earth. In this work he was the first scientist to argue effectively that geologic processes proceed over long spans of time

How old is the Earth? Scientists have determined the age of the Earth to be about 4.6 x 109 (billion) years old. 4,600, 000, 000 years = 4.6 x 109 years (scientific notations you should know) 109 = ______________ 106 = ______________ 103 = ______________ 1012 = _______________


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Relative Dating Techniques: Relative Dating: determining the age of a rock or fossil relative to the age of surrounding rocks and earth materials Relative Dating Laws -Original Horizontality - states that sediments are deposited in horizontal layers -Law of Superposition - states that in an undeformed sequence of strata, each bed is older than the one above it and younger than the one below it. -Principle of Cross-Cutting Relationships

Intrusions are younger than the rocks than the rocks that they intrude Extrusions are younger than the rocks they form above. Faults are younger than the rocks that they cut through

Relative Dating Techniques: Five Basic Laws! 1. Law of ___________________________________________________________________ 2. Law of ___________________________________________________________________ 3. Law of ___________________________________________________________________ 4. Law of ___________________________________________________________________ 5. Law of ___________________________________________________________________

THE PRINCIPLE OF UNIFORMITY: Geologists can infer events of the past by ________________________________________________________________________________

Uniformitarianism (Principle of _____________________________) : states that the forces that acted upon the ______________________ crust in the__________________ are the same as those that are ________________________ today.

****_______________________________________________________________****

Principle of Uniformitarianism

the physical, chemical, and biological processes that operate today have also operated in the geologic past; “The present is the key to the past”


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2. Law of Superposition- the principle that the _______________ layers in a sequence of rock strata must have been deposited _________________ the layers above, unless the rock strata have been ___________ or _____________. The __________rocks are found at the bottom. Geologists can date the ____________ ages of the strata from __________ to ___________ .

1. Law of Original Horizontality: ______________________________________________________________________________________________________________________________________________________________ If strata are _______________ then they must have suffered some kind of disturbance after they were deposited.

3. Law of Inclusions: A rock must first exist in order to be weathered, deposited and cemented as a ___________ in another rock. Therefore, If rock is composed of _________, the rock fragments must be _____________ than the rock in which they are found. _______ is older in A. _______ is older in B. The law of inclusions also applies to fossil preserved in bedrock. _____________________ are any naturally preserved remains or impressions of living things. They are found in ___________________________________, because____________________________________ ______________________________________________________________________________ Fossils give us information about _______________________________________.

Rock fragments (or inclusions) that are contained in another rock are older than the rocks in which they are found

Unconformity Buried erosional surfaces that are preserved in the rock record Create “gaps” in the geologic rock record


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4. Law of Cross-Cutting Relationships: Any ___________ or ____________ must be younger than ALL the rock through which it cuts. Simply put, the body of rock that is cross-cut had to be there first in order to be cut by an intruding igneous body or fault.

In general rock is always ____________________ than the process that changed it. Some processes include: _______________________, ____________________,

___________________, _________________________ & _______________________. These changes can lead to exceptions to the Law of Superposition: a. __________________________ is an igneous rock that formed from lava on the surface of the crust. An _____________________ must be younger than the strata below it, but _________________ than any layers above. b. _____________________ are created when molten rock ( ____________) is injected into older rock layers in the crust. ___________ are ____________ than all the rock layers in contact with them. c. ___________________ are bends in rock strata. _____________________ can overturn rock strata so that ______________ rock lies on top of _____________rock. Explain how folding can create an exception to the Law of Superposition. _____________________________ ________________________________________ d. _________________ are cracks in rock strata. _______________ produce offset layers. Which numbers are older than the fault labeled B? _______ Which are younger?__________ Processes that can change the order of rock strata: Rock strata must be _________________ than the process that changed it.

_________________, _______________ and __________________ __________________

are features created after rock or sediment has been deposited.


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Practice Activities Directions: List the age rock layers in correct age order from oldest to youngest.

5. Law of Original Lateral Continuity: When sediment is dumped by an agent of erosion, strata extends from the source of deposition until it gradually thins to zero, or until it reaches the edges of the basin of ____________________. This concept enables geologists to correlate outcrops of strata that has been dissected by processes of ______________.

_____________ Oldest _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ Youngest

_____________ Oldest _____________ _____________ _____________ _____________ _____________ _____________ Youngest


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CORRELATION OF ROCK STRATA: A. Correlation is ______________________________________________________________ _______________________________________________________________________________ Rock Correlation • Correlation is the process of matching rock units or events in separate rock formations • Correlation of rock units and geologic events can be based upon continuity, similar rock composition,

fossil evidence, and volcanic markers.

B. WAYS TO CORRELATE ROCK FORMATIONS: 1. “Walking the outcrop” is done by ______________________________________________ This is correlation by _____________________________________. Similarities in rock texture and composition can be used to match rock units over large areas

2. You can match the rock strata in one location with the rock strata in more distant locations by

________________________________________________. Fossils can be used to help match separated rock layers.

3. Time correlation compares ______________ ________________ contained in rock the strata.

4. The best index fossils:

a. ______________________________________________________ b. ______________________________________________________

This ensures that the fossils will have a wide horizontal and narrow vertical distribution

5. Another way of correlating layers by time is through ________________________________. Violent volcanic eruptions can emit large quantities of volcanic ash. The ash can spread out over a large area of land creating an excellent geologic marker for rock correlation. These ash falls are very __________________ events. A single layer of ________________ can be found over a large area, this allows geologists to make a ________________________ from one location to another at the position of a common ash fall.


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GEOLOGIC TIME SCALE: Geologists noticed that rock __________________________ could be identified by the fossils they contained. They also found that certain _____________________ were consistently located _____________________ or ______________________ other formations.

From these observations they established a __________________ ____________ ___________

With a sequence of fossil groups from _____________ to ______________each of these groups was named for a location where its __________________________ could be observed in the rocks. Example:___________________________

Further observations from around the world established a

_________________ ________________ __________________

based on _______________________________________________

AND _________________________ex:________________&______________ An _________________________ is the process of mountain building.

SEE PAGES 8 & 9 IN YOUR ESRT!!!

GEOLOGIC EVENTS OF THE PAST:

A. _________________________ causes gaps in the geologic record.

B. When a new layer of rock is laid down on a surface that has been____________________, it forms a buried erosion surface called an __________________________________.

C. How an unconformity forms:


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Absolute Dating: -Process of determining the exact age of a rock, fossil or Earth material in years before the present (as opposed to relative ages).

Common units are: millions of years ago = m.y.a = 106 billions of years ago = b.y.a = 109

-What were some of the techniques used to determine absolute time prior to the discovery of radioactivity? __________________________ and _______________________ -Modern science now uses radioactive isotopes to find the absolute ages of a given material (rock, fossil, etc.). -___________________________ – Instrument used in the detection and study of isotopes RADIOACTIVE DATING: A. Fossils enabled geologists to give __________________________ time. Relative time compares rock ages to _________________. Example: The limestone is older than the sandstone.

B. Measurements of natural _________________________ in rocks have allowed _________________ time scale to be an __________________ time scale.

The ________________ _______________ of an object is measured in years.

Example: The limestone was formed 2 mya (million years ago) and the sandstone was formed 1 mya.

Let’s review some basic chemistry to see how this works…

Radioactive Isotope Dating • An element is a substance consisting of atoms that are chemically alike. • Most elements exist in several different types of isotopes (atoms with a different number of

neutrons in their nuclei). • The nucleus (containing neutrons and protons) of radioactive isotopes is unstable and over time

they will emit particles and electromagnetic energy. This is known as Radioactive Decay, and changes the radioactive isotope into other isotopes or atoms. This occurs until, eventually a stable isotope forms.


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How can we use radioactive elements to date things? The rate of decay (breakdown) for any radioactive isotope is ______________. Over a given period of time, a definite fraction of the atoms of an isotope will ____________ ISOTOPE: ______________________________________________________________

_____________________________________________________________ Ex. C C

D. If the nucleus has more or fewer than the normal number of _________________, The isotope may be _______________________________.

E. Radioactive isotope will break down naturally into a lighter element called __________________ __________________ which is stable. *This process is called __________________________ _____________. RADIOACTIVE DECAY: When an unstable ______________ element changes into a completely different (but stable) ___________ element. F. A sample starts out at “Time Zero” with ________ percent of radioactive material. ( Time Zero: when the sample originally formed by cooling and solidification) As time goes by and the sample gets older, the radioactive elements decay, and ____________ radioactive atoms remain in the sample. Therefore, the higher the ratio of decay product to radioactive element the _______________ the sample. The ratio between the mass of the radioactive element and it’s decay product in a sample is called the ________________________ G. The decay of the parent atoms in a sample to daughter atoms is a _________ process. That happens at _____________ rates for different radioactive elements. Lets model this with pennies. H. The rate of decay of a radioactive element is measured by it’s ________ _______

HALF-LIFE: ______________________________________________________________ _____________________________________________________________________

Half Lives of Radioactive Isotopes • The rate of decay for any radioactive isotope is constant. • Over a given period of time, a definite fraction of the atoms in an isotope will decay to a

stable form. • The time required for half of the atoms in a given mass of an isotope to decay is known as the

half-life of the isotope. • Each radioactive isotope has it’s own characteristic half-lfe, which is not affected by any

environmental conditions, mass or volume. • The front page of the ESRT lists the radioactive isotopes, and information regarding their

decay and half-life.


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Complete the Chart using the front cover of the Reference Tables: RADIOACTIVE ELEMENT DECAY PRODUCT HALF-LIFE

1

Carbon-14

2

Potassium-40

3

Uranium-238

4

Rubidium-87

Selecting the Best Radioactive Element:

AGE OF SAMPLE RADIOACTIVE ELEMENT 1

Under 50,000 (RECENT)

2

Over 50,000 (OLDER)

Carbon-14 is used for dating:

_______________________________________ & _____________________________________

“Time Zero” for carbon dating begins when the organism ______________ or when the _________ burns out.

• Radioactive isotopes with very long half-lives are excellent for dating very old rocks, but for

younger objects, isotopes with shorter half-lives present a better tool to find accurate absolute ages.

• One such isotope is Carbon-14 , with a half-life of 5,700 years.

• C-14 dating – also called radiocarbon – can be used to date rocks and more importantly organic

remains up to approximately 70,000 yrs.

• This method has been used to date early humans, mastodonts, and many other geologically recent organic remains.

Can all rocks be dated using this technique? -Igneous and Metamorphic rocks work excellent for radioactive dating because at the time of crystallization (or recrystallization), a specific ratio of stable and radioactive isotopes are incorporated into the crystals. -On the other hand, sedimentary (clastic) rocks do not work well because they are composed of older, pre-existing rock fragments.


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Calculating the age of a rock: The ratio between the amount of the original isotope (parent) and the amount of its decaying product (daughter), is used to establish the absolute age of a sample. 1. What would be the age of the rock that has equal amounts of C-14 and its decay product N-14? 2. What % of the sample is radioactive after the following half-lives,

After 1 half-life:

After 2 half-lives:

After 3 half-lives:

3. After 11,200 years how much C-14 would remain in a 10 gram sample?

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