Geosciences - Assignment Essays

Geos 170A1 – Homework 1 – Age of the Earth

Due NO LATER than Monday, Jan 30, at 10:59 am, uploaded to the HW 1 folder under Assignments on d2l. It is worth 15 points total.

Instructions: You will need to refer to your notes from classes 1, 2, and 5, as well as the following articles, to complete this HW.

How Science Figured out the Age of the Earth by Paul S. Braterman, Scientific American, Oct 20, 2013.

https://www.scientificamerican.com/article/how-science-figured-out-the-age-of-the-earth/

How and archbishop calculated the Creation, Irish Times, Sep 25, 2003.

https://www.irishtimes.com/news/how-an-archbishop-calculated-the-creation-1.378556

1. Based on your reading of the above articles, and what we discussed in class, briefly describe two ways that people came up with an age for the Earth that are NOT based on the scientific method. (2 pts each)

2. What did James Hutton observe that led him to believe the Earth was infinitely old, with
“…no vestige of a beginning – no prospect of an end.” Explain in your own words what he thought was happening on Earth that meant it had to be old. (3 pts)

3. What does uniformitarianism mean? (2 pts)

4. In the mid-nineteenth century, Lord Kelvin estimated the age of the Earth based on the rate of heat loss from Earth and how long it would have taken to lose enough heat to form its solid rock and soil surface. He came up with an age that was way too young and not very precise (24 – 400 million years old). What was the big contributing factor/process going on in the Earth he did not consider when using only simple heat loss to calculate an age for Earth? (1 pt)

5. What is the accepted age of the Earth today, and what information/techniques did scientists use to get this number? (3)

___________________________________________ years old

6. Is the above age one that we can generally accept as true? Why or why not? (2 pts)

Bonus (one extra credit point): Explain in your own words how the factor Lord Kelvin neglected to account for would cause the age he calculated to be too young for the actual age of Earth.

Electromagnetic radiation (EMR)

Doppler Effect / EMR spectral shifts

Early observations of redshift in galaxies

The Hubble Plot

The Big Bang Theory

Origin of the Universe – the pieces of the puzzle
Please make sure to grab a handout for participation credit today.

Frequency – How many wave crests pass a given point per second.

Wavelength – Distance between two wave crests.

EMR: Energy that travels as waves (oscillating electric and magnetic fields). Can travel through a vacuum. Travels at the speed of light (roughly 300 million m/s).
Scientists think a lot about scale…

Longer wavelength
Shorter wavelength
Wavelength corresponds to energy: Shorter wavelength = higher energy (HOTTER).

Ex: UV light does damage to your body while radio waves do not.
1 nm = one billionth of a meter

The Doppler Effect

The Doppler Effect: Change in wavelength as an object moves relative to a STATIONARY observer.

Example: A siren or car horn sounds higher pitched as it approaches an observer and sounds lower pitched as it moves away from the observer.
THIS HAPPENS WITH LIGHT AS WELL

1 nm = one billionth of a meter

Blue shifted
Red shifted
Handout Page 1

In 1912 at Lowell Observatory in Flagstaff, Arizona, Vesto Slipher was the first to measure the redshift of spiral nebula (now known as a galaxies).

If the light emitted from the object has a different spectrum of light when it reaches Earth than it had when it first left the object = shifted.

Red shifted = toward red end of spectrum

http://spiff.rit.edu/classes/phys301/lectures/spec_lines/spec_lines.html

Slipher noticed that galaxies were red shifted. In other words, their light spectra were shifted toward the red end of the spectrum.

What question do you think he asked?
To clarify, red shift DOESN’T MEAN THEY LOOK RED!

The color of a star/galaxy doesn’t matter when looking at red or blue shift.

Look at spectra –> what other info do you see? Any questions come to mind?

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Vesto Slipher noted not only were they moving away from Earth but they were moving away at tremendous speeds! Pretty amazing for 1912!

Remember, red shift DOESN’T MEAN THEY LOOK RED!

The color of a star/galaxy doesn’t matter when looking at red or blue shift.

Handout page 2 (#6-12) – read the instructions carefully. Everything you need to know to answer the questions is in the very first paragraph! DON’T OVERTHINK IT!

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Vesto Slipher noted not only were they moving away from Earth but they were moving away at tremendous speeds! Pretty amazing for 1912!

In 1929, Edwin Hubble and Milton Humason put their observations together in a way that led to the first realization that the universe is changing over time –
OBSERVE the plot at right – what do you see?

Putting Data to Work
A scientist sees …

Relationship?
Slope?
Axes?
Pattern?

Recessional velocity  recede = move away from
So…what does this graph mean?
X-Axis:
Mpc = megaparsec

30 billion billion km
or
3 x 1019 km

Y-Axis:
km/s

For reference, the earth spins at 0.5 km/sec, which is 1,040 miles per hour.

Handout pp 3-4 – Expansion of the Universe

The Hubble Plot!
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The Big Bang Theory – came from the observations and data generated by Slipher, Hubble, Humason and others that indicated galaxies are moving away from us
Episode of rapid expansion (Big Bang) from a much more compact form, somewhere between 11 billion and 20 billion years ago (current best estimate is about 14 billion years ago)
Big Bang created simple elements (hydrogen, helium) from subatomic particles
Vast majority of Universe is Hydrogen (about 75%) and Helium (a little less than 25%)
Universe is still expanding

Turn in handout – name clearly on front page if you want credit for participation!

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What is a mineral?

What is a rock?

Three types of rocks and how they form.

Minerals: the building
blocks of rocks
A mineral:
is naturally occurring
is inorganic
has a definite chemical composition
has an ordered internal structure of atoms

Quartz
Minerals are made of elements
(Si, O, K, Al, Fe, Mg, Ca, C, Na, U, etc…)
THESE are the vessels for radioactive elements we use for age dating!

Ordered internal structure?

Silica tetrahedra: the building blocks of silicates.

Ex: Muscovite Mica
KAl2Si3O10(OH)2

Find a mineral on your table – how did you know it was a mineral?

The way the atoms arrange themselves controls the way the minerals grow. Silicates, the most common mineral type, all contain the basic silica tetrahedron. Sheet silicates grow in sheets, salt is cubic and grows in cubes.
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Muscovite: K Al2 Si3 O10 (OH)2

Biotite: K (Mg, Fe)3 Al Si3 O10 (OH)2

Mg and Fe = MAFIC minerals

Mafic  dark colored, higher density
Rocks = amalgamations of minerals. Rocks can also be mafic or felsic depending on what type of minerals they contain
Light colored rocks = felsic Dark colored rocks = mafic

We also look at the size/shape of the minerals in the rock to help classify it

Igneous, Sedimentary, Metamorphic

Both are the mineral Mica
Both are silicates (Si)

No Mg,Fe = Felsic minerals

Felsic light colored, lower density

Muscovite: K Al2 Si3 O10 (OH)2

Biotite: K (Mg, Fe)3 Al Si3 O10 (OH)2

Mg and Fe = MAFIC minerals

We also look at the size/shape of the minerals in the rock to help classify it

Igneous, Sedimentary, Metamorphic

Both are the mineral Mica
Both are silicates (Si)

No Mg,Fe = Felsic minerals

Felsic light colored, lower density
Handout part I: Minerals and Rocks (workbook)

Igneous rocks – rocks that cool and solidify from magma or lava.
Magma – below Earth’s surface; Lava – on Earth’s surface
Processes: melting, cooling, crystallization/solidification

Common igneous rocks:

Granite  Continents

Basalt  Ocean floor
Question – What does the color tell us?

Igneous rocks:
Cools and solidifies (i.e., forms) on the surface of Earth
Formed from lava (molten rock that erupts on surface)
Called volcanic or extrusive rocks – Texture = small crystals (cooled quickly)

Cools and solidifies (i.e., forms) inside Earth (molten rock that never erupts)
called plutonic or intrusive rocks – Texture = large crystals (cooled slowly, crystals had time to grow)

Form as lava or magma cools and crystallizes

Terminology alert!!

Look at these two rocks…similarities? Differences?
Can you find a rock on your table that you would call igneous?

Which of the following rocks clearly looks like it is made up of pieces/chunks of other rocks?

C.
A.

Sedimentary rocks
Form when sediment (pieces of a pre-existing rock, pieces of shell) is compacted and cemented together. Form in layers.
About 75 percent of all rocks on the surface of continents are sedimentary.
Processes = weathering (break down of rocks), erosion, deposition, compaction, cementation (lithification)

Can you find one on your table?

Metamorphic rocks
“Changed form” rocks. Produced from preexisting rocks.

Processes = heat and/or pressure unlike those in which the rock originally formed.

NO MELTING!

If these rocks melted and then cooled into rock again, they would be ______ rocks.
Granite = igneous
Gneiss = metamorphic
Handout – Rock types (workbook)
Find one on your table!

Metamorphism happens when rocks are subjected to heat, pressure, or chemical alteration. If rocks melted and then cooled into rock again, they would be igneous rocks.

Don’t forget to turn in your handouts for participation credit.

Name clear on front page!

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Geos 170A1 – Lecture 2 : Basic Geological Principles and the Geologist Perspective

As in all sciences, the Scientific Method is key to how we “do” geology.

Recall the pieces of the Scientific Method:

Observations

Ask a question or describe a problem to be addressed

Propose a hypothesis

Make predictions and test them

ITERATE (Science is a process…)

Analyze data

Report Conclusions

In geosciences, observations are key!

Geologists do a lot of field work, looking at rocks, minerals,

layers, mountains, faults, folds, glaciers, corals, and so much more.

Green River, Canyonlands (1871)
Green River, Canyonlands (1968)
Make some observations: Do you see a big geological difference from one picture to the next? (Handout #1)

How fast do things happen on Earth?
James Hutton (18th cent): modern concept of geologic time: Uniformitarianism
All land should be worn flat (by erosion) unless some process renews the landscape by forming new mountains.
“The present is the key to the past”: Geological processes (past and present) are slow.
Examples: Mountains grow mm per year, rocks are eroded mm-cm per year, Earth’s tectonic plates move cm per year.

Hutton came to these ideas by observing slow changes on his own land

James Hutton was a Scottish geologist, agriculturalist, chemical manufacturer, naturalist and physician. Often referred to as the ‘father’ of modern geology.
3

How fast do things happen on Earth?
Example: Mountains grow mm per year…

Let’s work this out: (Handout #2)

Mt. Everest’s peak is 29,028 ft above sea level
How long would it take Mt. Everest to “grow” to
its current height at a rate of mm’s/year?

Step 1:
Let’s round up to 30,000 feet
1 foot = 0.3 meters
1,000 mm = 1 meter

So…30,000 feet = ? mms (work this out)

James Hutton was a Scottish geologist, agriculturalist, chemical manufacturer, naturalist and physician. Often referred to as the ‘father’ of modern geology.
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How fast do things happen on Earth?
Example: Mountains grow mm per year…

Let’s work this out:

Mt. Everest’s peak is 29,028 ft above sea level
How long would it take Mt. Everest to “grow” to
its current height at a rate of mm’s/year?

Step 2:

We now know that 30,000 feet = ?,000,000 mm
(roughly…using rounding)

IF the mountain grew 3 mm / year, how many
years did it take for Everest to reach its current
height?

(in reality it took much longer and continues to grow today…)
Handout #3 and #4

James Hutton was a Scottish geologist, agriculturalist, chemical manufacturer, naturalist and physician. Often referred to as the ‘father’ of modern geology.
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Some important principles: “Relative Dating”

youngest
oldest
Original Horizontality- rocks are deposited in horizontal layers
Superposition – rocks at the bottom are the oldest
Tilting/folding is younger than deposition (i.e., it came after)

Faster water flow = more/heavier pieces moved
Water slows/stops = deposition in flat layers

(Activity #5 – Step 1)
Original Horizontality- rocks are deposited in horizontal layers
Superposition – rocks at the bottom are the oldest

Faster water flow = more/heavier pieces moved
Water slows/stops = deposition in flat layers

(Activity #5 – Step 2)
Original Horizontality- rocks are deposited in horizontal layers
Superposition – rocks at the bottom are the oldest

Some important principles: “Relative Dating”
Inclusion – younger rocks may incorporate pieces of older rocks

Cross-cutting relationships – older rocks may be cut by younger rocks or features (examples: intrusions of magma, faults)
older
older
younger
older
older
younger

younger
older

Faults- break in rock layers, motion on either side

The fault is YOUNGER than the rocks – the rocks had to be there for the fault to cut through.

It cross-cuts the layers

(Activity #6) Siccar Point, Scotland
James Hutton recognized its significance

Greywackes – base layers at Siccar point. Greywackes are sed layers formed in the ocean near fast rising mountains. They contain poorly sorted, angular grains of all types, the result of streams being uplifted and then downcutting rapidly, carrying all manner of material downstream and dumping it in the ocean.

Faults- break in rock layers, motion on either side

A
B
C
Handout #7

Look at this stunning photo of folded rock layers in France.

a. What are TWO geological events you can see documented? (Hint: these are one-word answers)

b. Which layer is oldest, and which is youngest (A,B, C)?

Oldest =

Youngest =
Turn in participation to a TA or Preceptor on your way out (IS YOUR NAME ON IT?)! Remember, there are no make ups on participation. These are easy points – come to class, participate, earn max. points!

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Geologic Time
Rates in geologic time
Relative Time
Numerical Time
Key events in Earth history
HW 1 – due next week on Monday, 10:59 am. Please note: HW should be completed in YOUR OWN WORDS! Copying/pasting from the internet or other students is a violation of the UA Code of Academic Integrity and will result it no credit for the HW and a report to the dean of students.

Remember these principles: “Relative Dating”

youngest
oldest
Original Horizontality- rocks are deposited in horizontal layers
Superposition – rocks at the
bottom are the oldest
Tilting/folding is younger than deposition
Inclusion – younger rocks may incorporate pieces of older rocks

Cross-cutting relationships – older rocks
may be cut by younger rocks or features
(examples: intrusions of magma, faults)
older
older
younger
older
older
younger

younger
older

We also use… Fossils
Certain fossils exist in a narrow time range but over a wide distribution on Earth.
Index Fossils

Example: Dinosaurs

Example – T Rex exists in Cretaceous rocks
3

Now we have an order of events, but what about numerical ages?

Where did the numbers on the geologic time scale come from?

have nuclei that spontaneously decay
daughter

parent

Radioactive isotopes
— emit or capture subatomic particles
parent: unstable, decaying radioactive isotope
daughter: stable radiogenic isotope

K40 Ar40
19 protons 18 protons

Proton converts to neutron via
electron capture

(Half-life is 1.25 billion years)

Half-life: time it takes for half the parent isotopes to decay (change) to daughter isotopes.
Example:

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Example – Potassium decays to Argon via electron capture

Carbon (14C) decaying to Nitrogen (14N)
Half-life of 14C = 5,730 ± 40 years

Half life = time it takes for half of the parent atoms to spontaneously decay to daughter atoms.

Half-lives are constant and known (have been measured).

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Decays by beta decay (emits a beta particle, either an electron or a positron). In the case of C14 it is electron emission. This is beta negative decay in which a neutron converts to a proton while emitting an electron and an antineutrino. Willard Libby – 1960 Nobel Prize

# half lives
Parent remaining
Daughter present
0
1
2
3
4
600 (total at start)
0
Handout – #s 1-10 only – let’s do it!
Once you have above filled in, method to find age:
1) Figure out how many ½ lives have passed based on amount of parent remaining and/or daughter present
2) Multiply the half life (known) by the number of half lives that have passed

Parent 300, 150, 75, 37.5. Daughter 300, 450, 525, 562.5.
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Rocks as clocks?

A mountain – made of rock
Half dome – used to be a magma chamber!
A rock like granite is chock full of minerals that incorporate radioactive elements when they form!
Zircon – a fantastic clock!
Incorporates Uranium into its structure when it forms from magma.

U-Pb age analyses
Rocks crushed, zircons extracted, and analyzed for their isotopic compositions, from which an age is calculated.

Images by George Gehrels, UA Geosciences

How can we date a very old rock?
Choose a chronometer with appropriate
time scale:

Isotope Half-lives Max ages:
14C: 5730 y 50 Ka
K-Ar: 1.3 Ga 4.5 Ga
Rb-Sr: 48 Ga 4.5 Ga
238U-206Pb: 4.6 Ga 4.5 Ga
235U-207Pb: 704 Ma 4.5 Ga
Sm-Nd: 106 Ga 4.5 Ga

Ka = thousand years
Ga = billion years
Ma = million years

Turns out, Pb is a great isotope to use to date rocks on Earth.

Handout #s 11-18 – GO!

4.1-4.3 Ga ages from Jack Hills of western Australia
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Formation of the Earth

Earth is about 4.6 billion years old, based on the
radiometric ages of meteorites and lunar rocks.

There were no rocks on earth at that time.
Type Number Dated Method Age (billions of years)

Chondrites (undisturbed H, LL, E) 38 Rb-Sr 4.50 +/- 0.02
H Chondrites (undisturbed) 17 Rb-Sr 4.52 +/- 0.04
H Chondrites 15 Rb-Sr 4.59 +/- 0.06
LL Chondrites (undisturbed) 13 Rb-Sr 4.49 +/- 0.02
E Chondrites (undisturbed) 8 Rb-Sr 4.51 +/- 0.04
Eucrites (polymict) 23 Rb-Sr 4.53 +/- 0.19
Eucrites 13 Lu-Hf 4.57 +/- 0.19
Iron (plus iron from St. Severin) 8 Re-Os 4.57 +/- 0.21

Oldest rock known on Earth dates at ~4.2 bill yrs.

Solid crust existed by 4.2 bill yrs ago

So…why do we say Earth is 4.6 billion years old and not 4.2 billion years old?

Recall our solar system discussion…meteorites…

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Timing is important: 14 billion for Big Bang event, then various ages for galaxies (10-13.6 bill)

But how old is our solar system?

Our Solar System = The planets, their moons, the Sun, the Asteroid belt, Meteorites

When and how did our solar system form?

The Big Bang Theory describes how the universe formed, NOT our solar system.

The Big Bang is the EVENT that began the rapid expansion that led to our universe

Scale is important! If the Sun were hollow, about 1 million Earths could fit inside it!

Solar System Formation

Inner versus Outer planets

Temperature and planet formation

Meteorites

Our Solar System
The Sun, Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, Pluto, Comets, Meteorites, Asteroids, planetary satellites (moons)

What is wrong with this diagram?

😫The sun is the wrong size (relative to the planets)
😫 The planets are not shown at their true size
😫 It is not to scale
😫 The distance between the planets is not shown correctly

How much of our solar system, in terms of total mass, does the Sun represent?
30%
50%
80%
99%

Solar System: Sun
Clouds of gas (H & He) & dust pulled together by gravity
Stars use hydrogen as fuel
Very high T/P
Fuses hydrogen atoms – nuclear fusion – to form helium

Clouds of hydrogen gas and dust in Eagle Nebula are incubators for the formation of new stars.

Question – where did the H and He come from?

Solar System Formation
Gas & dust pulled together by gravity  rotating disk
Star & planets form at the same time (4.6 Ga = billion years ago)

Inner vs Outer Planets
Terrestrial Jovian (AKA Gas Giants)
4 Terrestrial planets: Mercury, Venus, Earth, Mars

Eight Planets:
4 Jovian planets: Jupiter, Saturn, Uranus, Neptune
(Note Change of Scale)

A question scientists might ask: why are the inner and outer planets so different?

This gives a slightly better view…

Terrestrial
Jovian
WHY?
Rocky Inner Planets v. Gaseous Outer Planets (workbook/handout)

What does this graph show?

If you don’t know where to start, look at the axes!

X-Axis=AU
Astronomical Unit

1 AU = distance between earth and sun = 93 million miles.
Y-Axis=Kelvin
255 Kelvin = 0 F

AU = Astronomical Unit. Roughly the distance between the Earth and the Sun.
8

Temperature and Planet Formation:

What would happen if the gaseous planets were moved in closer to the sun?

Temperature is key.
What is the effect of solar heat on gases?
What about the effect of solar heat on rocks?

Solar System: Other (asteroids, meteorites)
Asteroid: Small (> 100m), planet-like body, mainly between Mars & Jupiter – left over from solar system formation

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NASA has a group that watches these. There are over 1200 potentially hazardous asteroids that pass near earth each year.

Meteorites formed at the same time as everything in our solar system. They tell us something about Earth…
Meteorite: Remains of meteoroids found on Earth.
Fall to Earth ~40k tons/yr
All formed at the time the solar system formed:
Type Number Dated Method Age (billions of years)

Reproducibility and Repeatability = Precision!

SCALE IS IMPORTANT!

Relative Sizes in the Universe (workbook/handout)

Sun’s diameter: 865,370 miles

–> 7,917 miles

How many Moons can fit across Earth’s diameter? In other words…Earth is how many times as big across as the Moon? ESTIMATE!!!

Look at the diameters above – you DON’T need a calculator = ROUND the numbers…

How many Earth’s can fit across Sun’s diameter? (i.e., the Sun is how many times bigger across than the Earth?). Again…rough estimate it!

Turn in workbook activities (handout) for participation credit. Make sure your NAME is legible on all pages.

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