Lecture 24. Forces Stabilizing Climate, Carbonate-Silicate Cycle.

1. Lecture 24. Forces Stabilizing Climate, Carbonate-Silicate Cycle. reading: Chapter 4

2. Forces Stabilizing Climate • 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?

3. 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˚

4. Forces Stabilizing Climate, cont. 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

5. 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

6. Mars at High and Low Tilt Angles high tilt angle today low tilt angle

7. 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 Where does most CO2 come from? } having a geologically active planet

8. Plate Tectonics

9. 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.

10. Silicate/Rock Weathering CaSiO3 + 2H2CO3 ---> Ca2+ + 2HCO3- + SiO2 + H2O silicate carbonic ions quartz rock acid 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.

11. 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.

12. Subduction CaCO3 + SiO2 ---> CaSiO3 + CO2 limestone quartz silicate rock metamorphic reaction: occurs at high T and P

13. The Carbonate-Silicate Cycle CO2outgassing 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

14. 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. } negative feedback loop

15. CO2 Constantly Replaced By Subduction

16. 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.

17. Lecture 25. Snowball Earth vs. Slushball Earth.. reading: Chapter 4