Transcript Lecture 24. Forces Stabilizing Climate, Carbonate

Lecture 24. Forces Stabilizing Climate,
Carbonate-Silicate Cycle.
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reading: Chapter 4
Forces Stabilizing Climate
1. Presence of an atmosphere
What happens on the Moon?
How does an atmosphere stabilize climate during day and night?
What happens when you have a ticker atmosphere?
What happens when you have a thinner atmosphere?
Seasons are Caused by Tilt (also called Obliquity)
ecliptic = plane of the
solar system
More solar radiation in the summer
Less solar radiation in the winter
Earth’s tilt angle: 23.5˚
Forces Stabilizing Climate, cont.
2. Having a large Moon
Moon very large compared to the Earth and other Moons.
The Moon stabilizes the tilt of the Earth.
This stabilizes the seasons.
animation
Forces Stabilizing Climate, cont.
Mars:
Currently Mars’ tilt is 25˚
No large Moons (2 tiny Moons: Deimos and Phobos)
Tilt is highly variable - chaotic.
Tilt varies between 0-60˚ on timescales of tens of
thousands of years/millions of years
ecliptic = plane of the
solar system
Mars at High and Low Tilt Angles
high tilt angle
today
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low tilt angle
Forces Stabilizing Climate, cont.
3. The Carbonate-Silicate Cycle
Unique feature of the Earth is a result of:
a. plate tectonics
b. volcanism
c. having oceans
} having a geologically active planet
Where does most CO2 come from?
Plate Tectonics
Forming Carbonate Rocks
CO2 + H2O ---> H2CO3
(carbonic acid, dissolved in rainwater
and in the oceans)
Ca2+ + H2CO3 ---> CaCO3 + 2H+
(limestone + acid)
Where is most of the CO2 in the Earth?
1x
tiny bit in atmosphere (270 ppm)
50x
dissolved in the oceans
30,000x
deposited as carbonate rocks (sedimentary rock)
1.7 millionx
dissolved in the mantle
If we were to put all carbonate rocks into the atmosphere, would
have an atmosphere similar to Venus.
Silicate/Rock Weathering
CaSiO3 + 2H2CO3 ---> Ca2+ + 2HCO3- + SiO2 + H2O
silicate
rock
carbonic
acid
ions
quartz
Another type of silicate rock:
2KAlSi3O8 + 2H2CO3 + 9H2O ---> 2K+ + 2HCO3- + 4H4SiO4 + Al2Si2O5(OH)4
feldspar
carbonic
ions
quartz
clay
acid
Acid weathering of rocks produces ions (Ca2+, K+, Fe2+, Mg2+, etc.).
Ions washed into rivers and the oceans (ocean salinity).
Clays and quartz are produced.
Ions combine with H2CO3 to produce limestone.
Forming Carbonate Rocks
CO2 + H2O ---> H2CO3
(carbonic acid, dissolved in rainwater
and in the oceans)
Ca2+ + H2CO3 ---> CaCO3 + 2H+
(limestone + acid)
Today:
Much of the limestone is biogenic (coral reefs, shells)
Some of the limestone is abiogenic.
Subduction
CaCO3
+
limestone
SiO2
quartz
--->
CaSiO3 + CO2
silicate
rock
metamorphic reaction: occurs at high T and P
The Carbonate-Silicate Cycle
1.
2.
3.
4.
5.
6.
CO2 outgassing from volcanos (greenhouse gas)
CO2 dissolves in rain, lakes, streams, turns into carbonic acid
Carbonic acid reacts with rocks, making ions, quartz, and clay
Ions and dissolved CO2 reacts to make carbonate rocks
Carbonate rocks are subducted
Subducted carbonate rocks turned into CO2
How Does this Cycle Stabilize Climate?
CO2 + H2O ---> H2CO3
(carbonic acid, dissolved in rainwater
and in the oceans)
Ca2+ + H2CO3 ---> CaCO3 + 2H+
(limestone + acid)
At high temperatures, more limestone is precipitated.
More CO2 dissolves in the oceans.
This cools climate and lower temperatures.
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negative feedback
loop
CO2 Constantly Replaced By Subduction
Earth’s Climate Is Obviously Not That Stable
1. The tilt undergoes precession (spinning like a top)
Alters how much solar radiation each hemisphere
receives during summer and winter.
Cycles: 20,000 years
2. There are small variation in the Earth’s tilt
21.5 to 24.5˚
Cycles: 40,000 years
3. Small variation (5%) in Earth’s eccentricity
Changes the distance to the Sun, higher heating when closer.
Cycles: 100,000 years
Milankovitch cycles - could
trigger ice ages.
Lecture 25. Snowball Earth vs. Slushball Earth..
reading: Chapter 4