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241 Cards in this Set

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1. What is the definition of intelligent life?
Any beings who develop their technology to the point where they send either their communications or themselves to Earth
2. Is there evidence for extraterrestrial intelligent life?
NO
3. What is astrobiology?
(Four parts)
1. Our ability to detect planets orbiting other stars is rapidly improving
2. Our understanding of how planets form is rapidly advancing
3. Studies of bacteria living in extreme environments have dramatically expanded
4. We have several places in our own solar system where we might find primitive life
4. What does the solar system consist of?
The sun, its 8 planets, a bunch of moons, an asteroid belt, and a couple of comet belts
5. What does the milky way galaxy consist of?
Includes our sun, 100 billion other stars, plus any planets, comets, etc., orbiting these stars
6. What does the universe contain?
The observable Universe contains some 100 billion galaxies in addition to our milky way
7. What is the key point regarding the size of the Universe?
A LOT of stars potentially hosting planets
8. How long would it take to cross the Milky Way Galaxy?
One Billion years
9. What is a light year?

At what speed does light travel?

How close/far is the nearest star to Earth?
One light year is the distance that light travels (in a vacuum) in a year

Light travels at 300,000 km/sec (186,000 miles/sec)

Nearest star is 4 light years away
10. What is light?
Part of the electromagnetic spectrum

*all electromagnetic radiation travels at the same speed (this would include radio waves)
11. What does all of this mean in terms of communication?
A radio message sent to a start 4 light years away would take 4 to reach the star

Any radio message we would receive today would probably be thousands of years old
12. Is the Universe expanding?
YES!
Hubble concluded that the Universe is expanding
13. How is expansion occurring?
Expansion is taking place ONLY between galaxies or relatively small galaxies

Thus, most galaxies are moving away from each other
14. What happens within a galaxy?
WITHIN a galaxy, gravitational attraction keeps stars in orbit around the center of the galaxy

Thus, gravity keeps a galaxy from expanding
15. How far is the Earth from the center of the Milky Way Galaxy?
28,000 light years
16. How did the Universe begin?
Began with an enormous explosion (Big Bang)

Big Bang hurled matter and energy outward and created the ever expanding Universe

*Before the bang the laws of physics break down
17. What is the age of the Universe?
13.7 +/- 0.2 Byr

13.7 Billion Years
18. How big is the Universe?
We don't really know

The edge of the observable Universe is 46 billion light years away from the Earth
19. What is nucleosynthesis?
The production of elements
20. What is an atom?
The smallest particles that can participate in chemical reactions
21. What are the parts of an atom?
Nucleus: protons and neutrons
-define element by # of protons

Electrons that orbit the nucleus
-electron shells make chemical reactions happen
22. What is weight % and atom %?
Weight %: percent of total mass taken up by a given element

Atom %: percent of all atoms taken up by a given element (same and mole %)
23. What is the average composition of the Universe?
Nearly all H
(75 weight % and 92 atom %)

Little bit of He and very little else
24. What is the relative abundance of elements in the Universe?
H, He, C, N, O, and Fe have the largest abundance
25. In order to explain the Universe what elements are necessary?
HUGE amounts of H and some He

Need other elements, with the heavy elements (esp those heavier than iron) being less abundant than the light elements
26. How were the first atomic particles formed?
Big Bang first produced just quarks BUT as the Universe rapidly expanded it cooled

Rapid cooling allowed for first atomic particles to form: Neutrons
27. How was the H formed then?
Further cooling allowed neutrons to radioactively decay into protons and electrons

Protons are nucleus of hydrogen
28. So then when did this H form?
H began forming within one second of the Big Bang

All of the H in the water in your body dates back 13.7 Byr to the very earliest moments of the Universe
29. How did the He form?
Four H atoms happened to fuse together and He was formed within the first 5 minutes of the Universe
30. What other elements are particularly important in order to make Earth?
Oxygen (O)
Silicon (Si)
Magnesium (Mg)
Iron (Fe)
31. What happened as the Universe further cooled?
Atoms and molecules gathered into huge patchy clouds call Nebulae
32. What happened to the nebulae?
When the nebulae clouds were cool enough, the force of gravity cause them to collapse to form stars
33. What is a protostar?
A growing sphere of super-hot H gas
34. How is the heat generated?
If the starting cloud is large enough, the central sphere will end up getting very, very hot
35. What is heat?
Atomic or molecular motion

Very hot atom/molecules move very fast
36. What happens to the central core of the protostar?
It becomes so hot that electron orbitals are destroyed (form a plasma instead of true gas)

Now, the naked H nuclei can interact through COLLISIONS
37. What is fusion?
When some energetic head-on collisions force the 2 positively charges protons to overcome their mutual electrical repulsion and combine to make a new element with 2 protons
38. What does fusion do then in term of making a star a star?
Fusion releases the heat that makes a star a star otherwise the star would just be a big ball of hydrogen

Fusion is when two nuclei combine (fuse) together and form a new element and release a HUGE amount of energy
39. How is the energy formed during fusion?
When two atomic nuclei combine, a tiny amount of mass is converted to energy

E = mc^2
40. What is the chemical reaction for hydrogen fusion?
ⁱH+ ⁱH+ ⁱH+ ⁱH = ⁴He
41. Where is H fusion the fastest?
In the core where temperature and pressures are highest
42. How does fusion expand the star?
The energy and subatomic particles released by fusion push the overlying layers outward

This is what expands the star
43. What happens when fusion in the core stops?
The whole star collapses toward the core

This free-fall (gravitational acceleration) toward the center heats up the interior enough to do two things
44. What two things happen?
1. H in the layers around the core ignite releasing so much energy that the star expands into a red giant

2. He produced in the overlying layers sinks to the core; core heats up so the He burning can begin
45. What is the reaction for He fusion?
⁴He + ⁴He+ ⁴He = C + NRG

⁴He + C = O + NRG
46. What happens when He runs out?
The core collapses again

He burning migrates up to a layer surrounding the core

H burning occupies the next higher layer
47. What's going on with the outer layers of the star at this point?
The outer layers are so far out that they are barely held by the gravity of the star
48. What happens with the carbon from the core?
The C is carried up from the core and carried away from the star in slow, cool stellar winds
49. What does the ejected carbon form?
It forms solid grains of dust called:

Interstellar dust grains
50. Do small or intermediate mass stars like our Sun burn carbon?
NO, because they cannot get hot enough
51. What happens to these small or intermediate stars like our Sun?
They end their live by blasting off their outer layers

They leave behind a slowly cooling sphere of mostly carbon coated w/ a thin layer of H and He
*these are called White Dwarfs
52. What do the cast-off layers make?
Planetary Nebulae

A nebulae is any big cloud of gas and/or dust
53. In summary how do planetary nebulae form?

(Four Parts)
1. Dying stars episodically blast off their outer layers
2. These layers form complex clouds of gas around the star
3. Gases are ionized & heated by radiation blasting from the star
4. Here central bright star is visible
54. In what types of stars form the rest of the periodic table of elements?
Large stars more than 8 times the mass of our Sun
55. In the red giant phase, what elements can a star burn?
Large stars can burn carbon and several other elements up to iron in a series of concentric shells
56. What happens when stars start to accumulate iron in their core?
The star only has a few days to live

When enough of the core stops producing energy by fusion, the whole star collapses inward
57. Once the star collapses inward what happens?

(two parts)
The central part of the star gets crushed forming an incompressible sphere of neutrons

Outer layers free-fall toward neutron core, strike core, violently rebound causing star to explode
58. What is this explosion called?
Supernova
59. What happens to the star after a supernova?
Much of the entire mass of the star (including manufactured elements) are blasted into space forming huge clouds of gas and dust (nebulae)

These nebulae = raw materials for next generation of stars
60. In short what are giant stars?
Element Factories
61. How many elements does fusion make?

How are the rest made?
Fusion makes nothing heavier than iron

Rest of elements are made by neutron capture
62. How does neutron capture work?
1. In red giant phase, lots of neutrons zip around
2. Neutrons regularly enter atomic nuclei
3. If too many neutrons enter a nucleus, one or more will radioactively convert to one or more protons = new element
63. Up to which element does neutron capture create?
During red giant phase, elements up to bismuth (Z=83) are produce by neutron capture
64. How are even heavier elements formed?
During the death blast of a supernova many neutrons are produced

Neutrons instantly blast into nuclei producing elements all the way up to uranium
65. So what produces all of the elements except for hydrogen?
Fusion plus neutron capture
66. Results of nucleosynthesis
Big Bang: H & He

Fusion: C, N, O, & Fe

Neutron Capture: up to Ur
67. Some final points on nucleosynthesis (three points).
1. Stars smaller than our Sun last at least 10 byrs before dying
2. Stars more than 8 times the mass of our Sun burn through their fuel in as little as 20 myrs
3. Small stars in red giant phase send of carbon rich soot. When they blast off their outer layers on their way to becoming white dwarfs they eject mostly H & He
68. What does nucleosynthesis mean then?
(three points)
1. H should be distributed throughout the Universe
2. Raw materials to make stars were and are universally distributed
3. Wherever we have star, we make new elements
69. So are there raw materials to build other earth like planets?
Likely that raw materials for rocky planets have been widely distributed for >10byrs
70. What are the four main steps in the formation of a planet?
1. Gravitational Collapse
2. Condense
3. Accretion
4. Differentiate
71. What is gravitational collapse?
A nebular cloud gravitationally collapses in a free-fall gas/dust
72. What does this
in-fall/contraction produce?

(two things)
1. Rapidly spinning central sphere (future star)

2. Rotating disk
73. Where does the material for the rotating disk come from?
Disk is built from material spun into orbit by the accelerating rotation of the contracting nebula
74. Is the rotating protoplanetary disk likely to start out hot or cold?
Hot because of friction

Inner disk ends up hottest b/c its farthest to fall and thicker
75. What happens when the disk get really hot?
It vaporizes everything so planet starts out as hot gas!

*gravitational in-fall heats everything up
76. What does the second step condense mean?
Must condense solids from cooling vapor
77. What is the general order temperature at which vapors condense?
Metals: condense at highest temp
Rocky Materials: middle temp.
Hydrogen: never condense
78. Where did condensation occur in our solar system?
Next to star: too hot for anything to condense
Near Mercury's (current)orbit: metals/rocks only cond.
Asteroid belt: metals, rocks, and rocky carbon compounds
79. Where was the 'frost line'?
Between asteroid belt and Jupiter

*line moves in and in as cooling occurs
80. What happens at the 'frost line'?
Beyond this: metals, rocks, rocky carbon compounds, and water ice/methane ice/ and other ices could ALL condense
81. Which planets had more solid to grow form?
The planets beyond the frost line

B/C ices are more than twice as abundant as metals and rocky materials
82. What were the results of the condensation phase?
Inner Four Planets: Rocky
(mercury, venus, earth, mars)

Outer Five Planets: Ice/Gassy
(jupiter, saturn, uranus, neptune, pluto)
83. If the nebula had cooled all the way what would have happened?
The inner planets would also be large and dominated by ice and/or gas
84. Where did all of the hydrogen go though?
Early stars have an early violent phase (T-Tauri phase) that produces intense solar wind and some outburts

These swept the H and He out from the inner solar system and vaporized/removed many H compounds b4 inner solar system cooled
85. What are the two main results of condensation phase?
1. Condensation by temperature nicely explains bulk composition of planets except for the lack of H gas in especially the inner solar system

2. Violet T-Tauri phase of early Sun drove out these gases into the outer solar system helping Jupiter and Saturn attain their impressive sizes
86. What is accretion?
The process by which solid particles in a planetary disk grows in size from dust to sand to asteroid to planetessiaml (baby planet) to planet
87. Why do the tiny particles rotating around a star in a protoplanetary disk stick together?
Due to chemical bonds and electrical forces
88. What happens as the particles grow?
Become massive enough to have their own gravitational fields
89. What is the importance of the gravitational fields?
These fields allow the first big dudes to win and become planets
90. If all planets grow in a single disk of material rotating around a central star; all planets should:
1. Rotate around the star in the same direction as the star
2. Rotate on their axis in the same direction as the star
3. Have moons that rotate around the planets in the same direction as the star
81. What is the orbital motion of the planets?
Perfect Order: all counter-clockwise orbit
82. What about planetary rotation?
5 of 8 go counterclockwise

Venus, Uranus, & Pluto have retrograde rotation
83. What about the rotation of the main moons?
4 are counter-clockwise

3 are not!
(Neptune, Uranus, & Pluto)
84. Why did this happen?
Accretion is Violent!

Venus, Uranus, & Pluto rotate slowly 'backward' b/c a large object struck a glancing blow during accretion
85. What evidence is there for collisions?
Mercury, Moon, Mar, & others are all heavily cratered

*Largest craters are mostly obliterated by younger ones
86. What are the dark areas on the moon called?
Maria

They are huge craters filled with lava flows
87. What does differentiate mean?
The separation of a planet (or asteroid or moon) into chemically distinct layer
88. What are the five layers Earth separated into?
1. Core: center; iron-nickel alloy
2. Mantle: dark green rock
3. Crust: thin layer of different rocks on top of mantle
4. Hydrosphere: oceans, ice sheets, & other reserves of liquid or solid water on Earth
5. Atmosphere: gaseous outer envelope
89. What are meteorites and what are the three types?
Meteorites are extremely old and preserve things from early phase of solar system

Chondrites, Metallic Meteorites, and Achondrites
90. What are Chondrites?

(Four points)
1. Have spherical masses called chondrules
2. Never found in Earth rocks (only assoc. w/ outer space)
3. Oldest rocks in solar system (4.57 Byr)
4. Never been differentiated
91. What are metallic meteorites?

(two points)
1. Made of iron and nickel

2. Slightly younger than chondrites
92. What are achondrites?

(Three points)
1. Rocky but lack chondrules
2. Diverse group
3. Most are same age as metallic meteorites
93. What is special about chondrites?
They are the most primitive objects in our Solar System

They were the raw building blocks of the rocky planets
94. What happens if you melt a chondrite?
Separates into blobs of iron and nickel that spontaneously combine to form a single mass of iron and nickel

Forms a core and rest forms a rock similar to the mantle
95. What are iron meteorites and achondrites considered?
Iron Meteorites = ancient cores of dead baby planets

Achondrites = ancient mantle of dead baby planets
96. What is necessary to do differentiate a planet made of solid
Melt it!
97. What are the three heat sources for melting a planet?
1. Impacts
2. Radioactive decay
3. Sinking of iron and rising of rocky melts
98. Summary points of gravitational collapse.
1. Form flattened disk
2. Need elements heavier than C to form Earth-like planets
3. Need nebulae that undergo several cycles of star-supernova-nebula-star-etc.
99. Summary of condense phase.
Inner disk = hottest
Outer disk = cooler and cools fastest
100. Summary of Planetary Formation.
Many planetary systems feature gas giants orbiting very close to their star
112. What happened in the last phase of accretion?
Massive collision

Small planet collided w/ Earth blasting a huge blob of molten rock into orbit around Earth
113. What was the blob?
Bits of Earth's mantle as well as Theia's

Became the Moon

*Theia's metallic core joined Earth's core
114. What was the surface of the earliest Earth like?
Entirely molten surface
-moon forming collision created this molten surface

Solid dark crust of rock began to form after this last heavy bombardment
115. Was there any volcanic activity on early Earth?
Hot early Earth supported almost continuous volcanic eruptions
116. What did these eruptions release?
Water vapor and other gases

These were incorporated during accretion
117. When did the ocean form?
Surface oceans by 4.4 byr ago

Data comes from grains of mineral zircon
118. Was the whole planet under water?
It may have been since the early crust was thin everywhere

Exception would have been where larger volcanoes breached the surface
119. What contributed the most to our oceans/atmosphere?
Volcanic out gassing

Icy comets may have also added a lot
120. What was the atmosphere like in the early Earth?

(three points)
Not breathable!

Contained: CO₂,NH₃,CH₄,SO₂,OH₂,N₂,H₂

Much denser and probably very, very cloudy
121. What is early history of the Earth based upon?
Evidence from meteorites, comets, the Moon and other planets
122. What are the oldest solids on Earth?
Zircon (tiny grains)

4.4 billion years old
*don't give a rich/detailed record of conditions at the Earth's surface
123. What are the earliest rocks recorded?
Oldest: 4.03 Byr

Several places where rocks date back to about 3.8 Byr

Rocks from 3.5 Byr to present form a relatively continuous succession
124. Why is the rock record so sparse?
Late Heavy Bombardment!
(bwt about 3.8 to 4.0 Byr)

*only zircon minerals were tough enough to survive times before 4 Byr ago!
125. What triggered the late heavy bombardment?
Gravity of Jupiter and Saturn may have flung Neptune from initial position near Saturn to current position beyond Uranus

This triggered a hail of debris from beyond the orbit of Uranus and Pluto
126. What was the effect of the late heavy bombardment?
Heavy impacts may have repeatedly vaporized oceans, extinguishing any early-formed life and destroyed the Earth's oldest rocks
127. What is of fundamental importance to the long-term habitability of the Earth?
Plate tectonics
128. What is plate tectonics?
Earth's surface is broken into a number of rigid plates that move around

Boundaries bwt the plates are where the action is: earthquakes, volcanoes, mountain belts, rift valleys
129. What are the three general types of plate boundaries?
1. Divergent Boundaries
2. Convergent Boundaries
3. Transform Boundaries
130. What are divergent boundaries?

What are the two types
Where two plates pull apart

1. ocean-ocean: called mid-ocean ridges or sea-floor spreading centers (most common type)
2. continent-continent: called a continent rift
131. What happens at mid-ocean ridges?
Plates grow (pull apart from each other at 2 to 15 cm/yr)

Instead of a gap forming bwt the plates, a series of volcanic eruptions produce new solid rock along the crest of the ridge (thus new crust is continuouslyouslly made)
132. What are convergent plates?

What are the three types?
Where two plates collide

1. ocean-ocean: subduction zone
2. ocean-continent: subduction zone
3. continent-continent: doubling of crust can produce very tall mountains
133. What happens at a subduction zone?
Two oceanic plates meet and one (usually the older one) is pushed under the other and sinks into the mantle

*subduction recycles sea floor
134. What forms on the overriding plate?

What else happens at subduction zones?
String of volcanoes form

Great place for earthquakes
135. What happens at a continent-ocean convergence plate boundary?
The oceanic plate always subducts under the continental plate
136. What forms at continent-ocean convergence plate boundaries?
A string of volcanoes forms on the overriding plate

A mountain belt may also form
137. What happens at a continent-continent convergence plate boundary?
One plate may try to subduct under the other but it can't b/c not dense enough
138. What is the result of continent-continent plate boundaries?
A belt of high mountains marking the zone of collision
139. What are transform plate boundaries?
This is where plates slide by one one another

Have continent-continent and ocean-ocean transform boundaries
140. What is the most famous transform plate boundary?
San Andreas Fault in CA (continent-continent)

*also mid-ocean ridges are offset by many small transforms
141. So keeping in line with plate tectonics, why is there a lack of pre-3.8 Byr rocks?
Takes long time for continents to form

Before 3.5 Byr all rocks were on oceanic crust

Sea floor subducts and nearly all rocks forming before 3.8 Byr were subducted (destroyed)
142. What is the rock cycle?
A process in which plate tectonics constantly makes new rocks and destroys old ones

Rock cycle is what has kept the planet habitable
143. What are the three types of rocks?
1. Igneous Rocks

2. Sedimentary Rocks

3. Metamorphic Rocks
144. How are igneous rocks formed?
Form when melted rocks cool and solidfy

Volcanoes are famous formers of fresh igneous rocks

Also form deep under ground
145. Where are rocks the melt to form igneous rocks located?

(two places)
1. Upper mantle

2. Older igneous, metamorphic, or sedimentary rocks in the crust
146. How do sedimentary rocks form?

What makes up sedimentary rocks?
From from eroded bits of older rocks

Made up of sand, silt, clay, and gravel

Other sed. rocks precipitate from sear water, either with or without the help of organisms
147. How do metamorphic rocks form?
Form when older rocks are recrystallized but not melted
148. What are the two common setting in which metaphoric rocks form?
1. A body of melted rock intrudes and cools nearby

2. Lots of rocks are metamorphosed deep under mountain belts (temp and pressures are high here)
149. What are the three way in which the rock cycle recycles rocks?
1. Melting of pre-existing rocks
2. Disintegration and recycling of rocks exposed at the Earth's surface
3. Recrystallization of pre-existing rock
150. What is the key point of the rock cycle?
An given rock type can get recycled back into the same type or converted into any of the other three rock types
151. What two things have made the Earth habitable?
1. Maintained a temp that has allowed liquid water to exist at the surface

2. Has an atmosphere rich in oxygen (necessary for multicellular life)
152. Liquid water implies what kind of temperature range?
Narrow range between 0°C to 100°C
153. What evidence exists indicating that the Earth has always supported liquid water?
(three things)
1. Chemical clues in zircon crystal 4.4 Byr old indicate liquid water at surface
2. Sedimentary rocks 3.8 Byr deposited in water
3. Water-lain sedimentary deposits 3.5 Byr and younger are found throughout geologic time
154. What is the one possible exception for Earth always supporting liquid water?
Ice seems to have covered the entire surface of Earth one or several time between 750 and 580 Myr ago

*deeper though oceans were liquid so only top portion frooze
155. What was the sun like 4.5 Byr ago?
Sun gave off 30% less heat
156. So why didn't Earth plunge into a permanent deep freeze?
Green House Effect

Warming is due entirely to atmosphere
157. What would Earth be like without any atmosphere?
Ave. Temp. of -17°C (1°F)

Today ave. temp. of +15°C
(59°F)
158. What are the three most important greenhouse gases in the atmosphere?
Water Vapor

Carbon Dioxide (CO2)

Methane (CH4)
159. How does the green house effect work?

(four points)
1. Sun emits electromagnetic radiation in UV, visible, and infrared wavelengths (most in form of visible light)
2. Visible light passes through atmosphere and strikes ground
3. Ground is warmed by visible light
4. Warm surface emits electro-magnetic radiation (heat) in infrared wavelengths
160. What is key to the greenhouse effect?
Incoming visible light is transformed into outgoing infrared light
161. What do the greenhouse gases do?
They absorb and re-emit this infrared light
162. What warms up the atmosphere and in turn the Earth's surface?
This sharing of infrared energy

*the warmer the atmosphere gets, the more infrared energy it radiates
163. What happens at stead-state?
The total amount of energy coming in from the Sun is exactly balanced by the infrared energy leaving the upper atmosphere of the Earth
164. What is going on today?
We have increased the concentration of CO2 and CH4 in the atmosphere

Thus, more energy is coming in than is leaving
165. What four things are volcanic gases from the Earth's mantle dominated by?
1. Water
2. Carbon Dioxide
3. Nitrogen
4. Sulfur Compounds
166. What was the ancient atmosphere rich in due to volcanic outputs?
CO2

Today's atmosphere contains only 0.35% CO2
167. What did the higher CO2 concentration do ?
Created a much stronger greenhouse effect

This is how Earth made do with 30% less solar energy
168. What is the total amount of carbon that could end up in the atmosphere due to normal biology and chemistry?

What about from volcanoes?
3.5 x 10^18 moles

6.9 x 10^18 moles

*volcanoes output TWICE as much CO2 as exists in ALL surface reservoirs today
169. What process removes exactly the amount of CO2 that volcanoes add every one million years?
Silicate mineral weathering plus the deposition of limestone
170. What is rock weathering?
Rocks exposed at Earth's surface weather

Minerals in the rocks are chemically attacked and mechanically break down such that the rock disintegrate (this is how soil forms)
171. What mineral weathering is vital to life?
Silicate mineral

Silicate minerals include all those that have oxygen and silicon as part of their composition

Silicate minerals dominate Earth's surface
172. What is the reaction that describes the weathering of a generic silicate mineral?
CaSiO3+ 3H2O+ 2CO2⟶Ca2⁺+HCO3⁻

1. CO2 from air is converted to HCO3⁻ dissolved in water (bicarbonate ion)
2. This water flows to ocean where it reacts with Ca to form limestone, water, and CO2
173. So what is the net reaction of silicate mineral weathering?
For 2 molecules of CO2 removed from the air by weather, one ends up forming sedimentary rock on the sea floor (CaCO3 is limestone); the other is recycled back into the ocean-atmosphere system
174. What is limestone?
1. CaCO3
2. Very common
3. Stores huge amounts of ancient CO2 that used to be in the atmosphere
175. What else stores ancient atmospheric CO2?
Coal and other fossil fuels

CO2 that was once in the Precambrian atmosphere is buried at solid rock and fossil fuels
176. What is meant by Precambrian atmosphere?
Oldest major period in Earth history

Stretches from 4.57 Byr to 542 Myr
177. Since volcanic activity varied a lot, how did weathering and limestone burial vary in such a way as to closely balance changes in volcanic output in order to avoid the atmosphere getting too much or too little CO2?
Has to do with chemical reaction rates varying with temperature

*every 10° C rise in temp doubles or triples reaction rate
178. How did this reaction rate varying work?
Volcanoes put out more CO2, climate warms up, rates of chemical weathering speed up

Faster weathering leads to faster burial of CO2, climate cools

Conversely, cool climate, weathering slows, and more CO2 builds up, climate warms
179. How does plate tectonics affect the climate?
Most volcanoes erupt along plate boundaries result of plate motion (stop P.T. and volcanic CO2 emissions drop a lot)

Continental collision & volcanic eruptions create new mountains, exposing fresh rock to weathering (w/o P.T. landscape would erode flat, rock weathering slow a lot)
180. Do other planets have plate tectonics?
No, Earth is uniquely geologically active
181. Why don't Mercury, Mars, and the Moon have plate tectonics?
Small size means they cooled off fast

Interiors were not hot enough to have rocks soft enough for tectonic plate to move around
182. Venus is close to Earth's size so why does it not have plate tectonics?
Earth is a uniquely wet planet
Water is essential to the igneous processes that grew the continents that expose rocks to weathering

Addition of water to mantle by subduction zones has kept the mantle fluid enough to allow plates to move
183. Why do we have oxygen in our atmosphere today?
Due to sunlight-driven photosynthesis in plants

Plants actively maintain O2 in our atmosphere
184. What gases did the early Earth atmosphere contain?
CO2, SO2, H2O, N2, CH4, NH3, and H2

NO OXYGEN!
185. How do we know early atmosphere lacked O2?
Deposits older than 1.8 Byr include sandstones with uraninite (UO2) and pyrites (FeS)

Both minerals rapidly break down in presence of O2
186. What is the snowball Earth hypothesis?
An illustration of how the Earth system regulates its own climate
187. Where are the coldest places on Earth?
Polar regions (Antarctica, Arctic areas)

High elevations (snow-capped peaks)
188. What happens during a typical ice age?
Ice sheets and glaciers advance from their normal homes down into warmer climates
189. How was the last ice age (100,000 yrs ago) triggered?

(parts 1-4)
1. Oceans sucked up atmospheric CO2
2. Warm surface waters in N. Pacific provided moisture (snow) to cooling N. Canada
3. Canada became very white
4. White snow reflects back a lot of visible light
190. How was the last ice age triggered?

(parts 5-7)
5. Higher albedo (expansion of area of year-long snow in Canada) reflected back more sunlight, further cooled
6. Cyclic effect were cooler, more snow, more heat reflected
7. Snow packs thickened and bottom layers compressed into solid ice
191. How was the last ice age triggered?

(parts 8-9)
8. Thick ice flows
9. Snow packs turned into vast glaciers called ice sheets
192. How did the ice age end?
After 100,000 yrs of growth, ice sheets destabilized and collapsed, ocean circulation was affected, and CO2 returned to atmosphere
193. In comparison to recent ice ages were ice sheets formed near the poles, where did glacial deposits form between 750 and 580 Myr ago?
Located in the tropics

Tropical glaciation does appear to have happened
194. What evidence is there for 'Snowball Earth' ice ages?
1. Glacial striations

2. Dropstones
195. What are glacial striations?
Distinctive scratches made in rocks when they are dragged against each other by glaciers
196. What are dropstones?
Icebergs that float over lakes or oceans drop gravel or boulders where otherwise only very fine-grained sediments accumulate
197. What is albedo?
The amount of sunlight reflected back into space as visible light (i.e. not able to trigger the greenhouse effect by warming surface and radiating IR light)
198. An ice-covered planets has such a high albedo it's tough to image how it could ever warm up. So how did it thaw out?
Emissions of volcanic CO2 pumped up atmospheric CO2 concentrations to where they overcame the incredibly high albedo and warmed the planet

As ice sheets melted, albedo decreased, more visible light was absorbed, planet got hot
199. How come volcanoes still erupted when it was so cold?
Volcanism is fueled by internal heat

Erupt regardless of whether climates are hot or cold
200. How does weathering play a role?
All the rocks are under snow or ice so rates of chemical weathering drop to zero

Shut down all-important sink of volcanic CO2
201. When the planet began getting hotter faster, what happened to chemical weathering?
Sped up weathering, which increased flux of Ca & HCO3- to oceans

Limestone (normally hot climates) deposited directly on glacial deposits
202. When is this sequence of limestone over glacial dropstones typical?
Typical of interval from 750 to 580 Myr

Such deposits are rare for the rest of the glacial intervals

Very odd to have hot-climate rocks deposited directly on cold-climate rocks
203. So what is the sequence of the Snowball Earth Hypothesis?
1. Polar areas freeze up
2. Ice sheets spread to tropics
3. Temp's drop; oceans freeze
4. Entire surface freezes
5. CO2 induced warming
6. Back to normal
204. What is an isotope?
An isotope of an element has the same number of protons, but they have variable numbers of neutrons in the nucleus
205. What are some common isotopes?
Carbon: C¹², C¹³,C¹⁴

Uranium: U²³⁵& U²³⁸

*235U is more radioactive than 238U
206. When is an isotope radioactive?
If its nucleus is unstable

The nucleus is unstable if it has too many (or too few) neutron relative to protons
207. Which elements have roughly equal neutrons and protons?

Which elements show larger excess of neutrons?
Light elements

Heavier elements
208. During radioactive decay, what three things can happen?
1. Alpha Decay
2. Beta Decay
3. Electron Capture
209. What is alpha decay?
2p & 2n are ejected as a He nucleus

He nuclei are alpha particles (=radiation)
210. What is beta decay?
Neutron decays into a proton and ejects an electron

Electron is the beta particle (=radiation)
211. What is electron capture?
An electron falls into the nucleus and converts a proton into a neutron
212. In each case of radioactive decay what two things occur?
1. Various types of radiation are created

2. One element is converted into another
213. How are rocks dated?
Based on the radioactive decay of one isotope (parent) into another (daughter)
214. What are decay rates?
They give the proportion of the starting number of radioactive atoms that decay in a year

Also called decay constants
215. Why are decay rates called decay constants?
Because radioactive elements decay at constant rates
216. Radioactive decay is what kind of process?

Why?
Probabilistic Process

We never know when a particular single atom will decay
217. Why do decay constants work then?
Because we're talking about huge numbers of atoms

Chances are that some fraction of them (determined by the decay constant) will decay in the next second
218. What is half-life?
How ling it takes one-half of the starting amount of a given parent to decay to its daughter
219. How do parents decay?

How do daughters accumulate?
Parents decay away at a constant rate

Daughter accumulates at the same constant rate
220. What do radiometric dates record?
The time since a given rock or mineral solidified from a liquid state
221. To give an accurate age what is essential?
The rock or mineral always remained a closed

It can NEVER have gained nor lost any parent or daughter or no accurate age is obtained
222. What are the two most powerful parent-daughter systems?
1. Potassium-argon
40Ar → 39Ar
(base on 40K → 40Ar)

2. Uranium-lead
238U → 206Pb & 235U → 207Pb
223. When a mineral crystallizes in a magma does it pick up K or Ar?

Why?
Picks up K

K is chemically active element, whereas Ar is noble gas and inert
224. Thus, what do freshly formed igneous minerals contain?

What happens over time?
K (parent) but no Ar (daughter)

40K decays and 40Ar accumulates
225. How do we get the age?

What's wrong with this?
Measure relative proportion of the two, take into consideration half-life, and get age

Problem is ratio is of elements in two different states (liquid and gas)
226. How do we solve the problem?
Measure 40Ar/39Ar ratios

Irradiate a sample with neutrons and 40K is turned into 39Ar
227. What mineral commonly found in igneous rocks sucks up uranium?
Zircon

Suck up huge amount of U but little or no Pb
228. How do we measure age using this?

What's the problem here?
Measure the relative amount of U and Pb to get an age

Have two parents and two daughters
229. How do we solve the problem?
Algebra involving equations that govern the change in parent/daughter isotopes

Make graphs indicating when a given sample has gained or lost parent and/or daughter
230. What are inherited daughters?

In which cases is this common?
A mineral forms with daughter isotopes already in them

Common especially with Rb-Sr and Sm-Nd dating
231. What do we measure in Rb-Sr dating?

How do we do this?
Measure ratios rather than absolute concentrations of a particular isotope

Divide through the equation by an isotope not produced by radioactive decay (86Sr in this case)
232. What equation is used?
Equation of Line:
y = b + mx

(87Sr/86Sr)t = (87Sr/86Sr)i + 86Rb/86Sr x (e^λt - 1)
233. What is the 87Rb/86Sr ratio when rock forms?
When a bunch of mineral crystallize from a liquid magma, each different mineral picks up a distinct Rb/Sr ratio

This gives a range of values across the x-axis
234. What is the 87Sr/86Sr ratio when a rock forms?
Identical when a bunch of different mineral crystallize in a magme

No spread on y-axis
235. As time passes, what happens to the two ratios?
87Rb decays to 87Sr

Thus, 87Rb/86Sr ration decreases and 87Sr/86Sr ratio increases
236. How does the 87Sr/86Sr ratio increase?
It increases proportionally to the 87Rb/86Sr ratio

Thus, high Rb/Sr ratios see faster increase in 87Sr/86Sr
237. What does the slope of the line give?

What happens when the rock containing the mineral gets older?
Slope of line gives the age of the sample

Older the rock, steeper the slope of the line
238. What is an isochron?
A linear array of parent-daughter isotope data
239. In order to calculate the age what do you solve?
solve m = (e^λt - 1) for t
240. What are the best rocks to date?
Igneous rocks

Sedimentary and metamorphic rocks are more difficult to date for a variety of reasons
241. What are igneous rocks the best rocks to date?

(three reasons)
1. A magma or lave tends to be very well stirred so isotope ratios are the same at each and every spot in the magma
2. When the minerals form they tend to have different parent-daughter ratios but identical daughter isotope ratios
3. Tend to crystallize over a short period of time making a nice single 'event' to date
242. What is the best way to date the fossil record?

Why?
Find areas where ancient volcanoes blasted ash into the nearby sea

Volcanic ashes often contain K (Ar-Ar dating) and zircon (U-Pb datin)