Why is Earth Habitable The Goldilocks concept

1
Why is Earth Habitable? The Goldilocks concept
2
The Earths radiation budget
3
Why is Earth Habitable? The Goldilocks concept

• Venus receives almost twice as much radiation as
  the Earth
• But sulfuric acid atmosphere on Venus reflects
  80 of radiation
• Earth reflects 26
• Why is Venus so hot? Atmosphere is 96 CO2
  runaway greenhouse effect
• But Venus and Earth contain the same amount of
  carbonwhat is the difference?
• HOW the carbon is stored
• Venus-carbon in atmosphere
• Earth-carbon in rocks

4
The faint young sun paradox

• Was the Earth frozen for 2 million years?

5
Reminder the carbon cycle
6
The faint young sun paradox

• Was the Earth frozen for 2 million years?
• Nogeologic evidence of running water
• Evidence of ice 2.3 Byr, but local glaciations
• Continued presence of life on Earth does not
  support frozen Earth idea
• Why was the Earth not frozen for the first 2
  billion years??

7
Ancient ripple marks in Precambrian sandstone in
the Grand Canyon
probably Shinimu, mile 77.
8
Snowball Earth????
9
(No Transcript)
10
The faint young sun paradox

• Was the Earth frozen for 2 million years?
• Nogeologic evidence of running water
• Evidence of ice 2.3 Byr, but local glaciations
• Continued presence of life on Earth does not
  support frozen Earth idea
• Why was the Earth not frozen for the first 2
  billion years??

11
Hummm. . .. Is the greenhouse effect our
thermostat?
12
Slow carbon exchange and climate change

• The larger the reservoir, the slower the exchange
  rate of carbon
• All reservoirs exchange with the atmosphere
• We are going to focus on SLOW carbon exchanges

13
Slow inputs of carbon from volcanoes
14
Slow inputs of carbon from volcanoes

• What balences this release of carbon from
  volcanoes?
• WEATHERING

15
Weathering

• What is weathering?
• Chemical weathering is chemical decomposition
• Breaking down and restructuring of chemical bonds
• Why should you care about weathering for this
  class?

16
Weathering and Erosion

• What is the difference between weathering and
  erosion?

17
What components of the Earths atmosphere and
hydrosphere affect weathering?

• Oxygen
• Carbon dioxide
• Water

18
What components of the Earths atmosphere and
hydrosphere affect weathering?

• Oxygen
• Carbon dioxide
• Water
• H20 CO2 -H2CO3 - H HCO3-

Carbonic acid Weak acid, but very important in
dissolution
19
Slow removal of carbon by weathering
20
Types of chemical weathering hydrolysis

• hydrolysis is the most important process in the
  weathering of silicate minerals
• CO2 H2O H2CO3 (carbonic acid) H
  HCO3- (bicarbonate)
• the most common weathering reaction on earth is
  the hydrolysis of feldspars producing clay
  minerals
• e.g. K-feldspar kaolinte
• From book (pg. 93)
• CO2 H2O H2CO3 (carbonic acid)
• CaSiO3 H2CO3 (carbonic acid) ? CaCo3 SiO2 H20
• CO2 is REMOVED FROM ATMOSPHERE!!!!!

21
Types of chemical weathering hydrolysis

• The reaction between mineral elements and the
  hydrogen ion of dissociated water.
• Important mechanism in breaking apart structures
  of the silicate minerals.

22
carbonation (dissolution weathering)

• dissolution of calcium carbonate (limestone) in
  acidic soil and groundwater
• carbonation of limestone results in karst
  topography
• Dissolved limestone represents the largest
  constituent of the dissolved load of most rivers
• CaCO3 H2CO3 Ca2 2HCO3-
• Ca2 gets incorporated back into marine shells
  (CaCO3 )
• 2HCO3- is returned to atmosphere as H20 and CO2
• NO LONG TERM STORAGE OF CO2

23
Controls on rates of chemical weathering
temperature

• reaction rates are higher at higher temperatures
• Weathering rates double for every 10 0C
  increase in temperature

24
Controls on rates of chemical weathering
precipitation

• Chemical weathering occurs in a solution water
  is the agent of chemical weathering.

25
Controls on rates of chemical weathering
organic material

• Vegetation enhances rates of chemical weathering
• Plants increase CO2 concentrations in soils.
• CO2 H20 ? H2CO3 (carbonic acid)
• soil air is greatly enriched in CO2 by decay of
  humus
• up to 30 of soil air is CO2 as compared to 0.03
  of the atmosphere
• biogenic CO2 is the major source of carbonated
  groundwater

26
Carbonic acid and weathering
27
Chemical weathering Chelation Organic complexes
aid in dissolution, produced by alteration of
humus in plant acids and excreted by lichens.
28
Chemical weathering Chelation Organic complexes
aid in dissolution, produced by alteration of
humus in plant acids and excreted by lichens.
29
Controls on chemical weathering
30
Controls on rates of chemical weathering
surface area
31
Particle size and surface area
32

• Kinetic controls on weathering (reaction speed)
• 1. concentration of reactants. If there is
  equilibrium (example, Na in water), then the
  reaction stops. What would prevent this
  equilibrium from happening? Leaching.
•  
• 2. reaction rates are higher at higher
  temperatures.
•  
• ability of materials to move diffusion. Cant
  move, cant be Removed.
• Example,
• weathering rind.

33
Feedbacks and chemical weathering
34
Feedbacks and chemical weathering
35
(No Transcript)
36
The Gaia Hypothesis

• Hypothesis that life regulates the climate on
  Earth
• Support for hypothesis
• carbon is basis of CO2 thermostat and is basis of
  life
• Land plants enhance weathering in soil
• Plankton extract CO2 to form their shells
• Progression towards more life ? enhanced
  weathering ? less CO2 in atmosphere helps
  counterbalence strengthening sun

37
The Gaia Hypothesis

• Criticism of hypothesis
• No known record of life before 3.5 Byr
• Complex life forms are relatively recent

38
Oxygen on Earth

• Oxidized iron minerals appear 2.3 Byr
• Where did oxygen come from?
• Likely from photosynthesis of marine organisms

39
BIFs! (Banded Iron Formations

• Banded iron formations are very large bodies of
  sedimentary rock laid down some 2.5 billion years
  ago.
• At that time, the Earth still had its original
  atmosphere of nitrogen and carbon dioxide.
• The black parts are thin layers of dark,
  semi-metallic hematite or magnetite (IRON OXIDES
  Fe2O3 )
• the red layers are jasper, an iron-rich chert.

40
Plate tectonics and climate
41
(No Transcript)
42
(No Transcript)
43
N
S
44
S
N
45
(No Transcript)
46
Paleomagnetic signal in ocean crust

• 300 Myr (500 Myr) to present
• Orientation of magnetic compasses can be used to
  reconstruct past locations of continents
  (latitude but not longitude)
• 175 Myr to present
• Can determine rates of spreading, and estimate
  rates of creation and destruction (subduction) of
  Earths oceanic crust

47
AGE OF THE OCEAN FLOOR CRUST

48
(No Transcript)
49
ridge axis
ICELAND

Ridge
Reykjanes
50
Plate Driving Forces
51
The polar position hypothesis

• 1) Ice sheets should appear on continents when
  they are at or near the poles
• 2) no ice should appear on Earth if no continents
  are at or near the poles
• We can test this hypothesis by looking to see if
  records of past glaciations correspond with times
  when continents were near the poles

52
Major ice sheets over last 500 Myr

• 430 Myr
• 325-240 Myr
• Current icehouse 35 Myr-present

53
Gondwana!
Pangaea!
54
Problems with hypothesis

• No glaciations 425-325 Myr, even though Gondwana
  was at South pole

55
BLAG Tectonic control on CO2 input

• So. .. Geographic position of continents cant
  fully explain major shifts in climate over last
  500 Myr
• BLAG (Berner, Lasaga and Garrels) hypothesis
  climate changes over million year timescales from
  changes in rate of CO2 input driven by PLATE
  TECTONICS
• Changes in RATES of spreading and subduction
  changes rates of CO2 input to atmosphere

56
(No Transcript)
57
BLAG hypothesis

• CO2 is emitted at ocean spreading centers (ocean
  ridges)
• CO2 is emitted from volcanoes above subducting
  plates
• CO2 is emitted from hot spots in the middle of
  plates

58
AGE OF THE OCEAN FLOOR CRUST

59
BLAG hypotheses
60
BLAG hypotheses

• Plate tectonics primary driver, but involves
  chemical weathering for negative feedback to
  moderate changes

61
BLAG hypotheses

• In BLAG hypothesis, carbon is cycled between
  rocks, ocean critters, atmosphere, rocks. . .

62
The uplift weathering hypothesis

• Weathering is KEY! Weathering is an active driver
  of climate change
• Hypothesis that rate of weathering is affected by
  availability of fresh rock and mineral surfaces

63
Controls on rates of chemical weathering
surface area
64
(No Transcript)
65
(No Transcript)
66
The uplift weathering hypothesis

• Case study Wind River Range
• Exponential decrease in mean rate of weathering
  on moraines

67
Glacial deposits

• Glacial moraines
• Ridges of sediment deposited on sides (lateral
  moraines) and ends (terminal moraines) of
  glaciers
• Moraines form by glacier dumping material at the
  same location over time (conveyor belt), and
  pushing material in front of moving ice
  (bulldozer)
• Glacial deposits mark where a glacier has been in
  the same place for a period of time.

68
The uplift weathering hypothesis

• Case study Wind River Range
• Exponential decrease in mean rate of weathering
  on moraines
• Why?
• Fresh rock, more weatherable material (biotite,
  mafic minerals)
• Ground-up rockmore surface area to weather

69
Uplift and weathering

• Uplifted areas are areas of increased erosion
• Steep slopesincreased mass wasting
• More frequent earthquakes
• Focus of orographic precipitation
• Glacial processes increase erosion
• These processes increase weathering and draw out
  CO2

70
Processes moving material downslope
Fall Very steep slopes, material is out of
contact w/ slope much of the way down, may break
on contact debris accumulationTALUS Slide No
internal deformation. Translational slide plane
of movement is straight, material does not
change orientation Rotational slide (slump)
plane of movement is curved, material rotates as
it moves. Flow More fluid motion does not
move as an intact mass, mixes as it moves.
Difference in velocity from the base of the slow
to the top, moving faster at the upper surface
than the baselaminar flow, streamflowturbulent
flow. Wash overland flow, common on bedrock,
sparse vegetation
71
Geomorphic Response to Fire
Saturation-induced failures
Runoff generated events
72
How do debris flows move such big rocks?
73
Slumgullian Debris Flow San Juan Mountains,
Colorado. (lower velocity, high of clays)
74
Vallée de la Sionne, Switzerland 
http//www.cs.umd.edu/class
75
(No Transcript)
76
Hebgen Lake Montana

• Magnitude 7.5 earthquake triggered an enormous
  landslide that buried a campground, causing 28
  deaths and dammed the Madison River, forming
  Quake Lake.

http//neic.usgs.gov/neis/eq_depot/usa/1959_08_18_
pics_2.html
77
Uplift and weathering

• Uplifted areas are areas of increased erosion
• Steep slopesincreased mass wasting
• More frequent earthquakes
• Focus of orographic precipitation
• Glacial processes increase erosion
• These processes increase weathering and draw out
  CO2

78
Where does this happen?

• Subduction of oceanic crust (but this is always
  happening)
• Continent-continent collision!
• Tibetan Plateau! (collision last 55 Myr)

79
Is the hypothesis supported?
80
(No Transcript)
81
(No Transcript)