What is p16164 really about? New and improved! 1) When CO 2 dissolves in water, some reacts with water to produce acid and ions, making gas exchange NOT just CO 2 (g in atm) <-> CO 2 (aq in ocn) 2) If CO 2 increases, ocn can uptake more than it otherwise would. But this acidifies the ocn. 3) Increasing acidity depletes CO 3, lessoning (buffering) acidification somewhat. 4) Plankton and coral dissolve when CO 3 becomes scarce (or undersaturated) What is p16164 really about? New and improved! Good thing: ocn can take up anthropogenic CO 2 Bad thing: ocn acidifies (ie increase H + ) Why is this bad? Ask a plankton! Their shells tend to dissolve when CO 3 is depleted because: CO 3 + Ca + <-> CaCO 3 (not obvious from book) (Currently plankton shells dissolve very little in the upper ocn, but we worry about the future) Chapter 10-11* -Brief History of the Atmosphere 1. Presently there is enough O 2 to oxidize everything in sight. Early on there wasn t. 2. First life, at least 3.5 billion years ago (b.y.), depleted CO 2 and made CH 4 Atm constituents in order by % Advanced Life 3. O 2 Photosynthesis originated ~2.7 b.y., and CH 4 must have nearly disappear (like today) *Know this much of it. The rest makes a good story, but it is not required reading. Fig 11-3 Tree of Life Chapter 12 - Long term climate regulation Single Cell Organisms Higher plants and animals Arose at Cambrian explosion Methanogens first life, generate CH4 Do not tolerate O2 Advanced Life How could the climate be warm enough to support liquid water? 1
Faint Young Sun Revisited Possibility 1 How to keep Ts big enough? 1. Lower albedo 2. Other heat source AND/OR 3. Increase Greenhouse effect Planetary Energy Balance S (1-A) / 4 + F OTHER = σ T E 4 Planet Greenhouse Effect T S = T E + ΔT g A would have to be ~0 to compensate for 30% reduction in S Water covered planet has nearly zero SURFACE albedo But it would be cloudy Can you think of a way? Possibility 2 Possibility 3 F OTHER? Geothermal is too small Recall Pluto F OTHER need only be large locally, say via horizontal heat transport! But to make a hot spot, we need heat to go from cold to warm. an you think of how to do this? Increase Greenhouse Effect? But which gas? Case for CO 2 Impact and vaporization of planetesimals Increased volcanism Smaller continents with less weathering Fig 13 Amount of CO 2 needed to make Earth at least partly ice-free while accounting for S Is that much CO 2 possible? (80+ C for bacteria) Rocks could supply 60 bars of CO 2 to atmosphere (so yes!) 2
CH 4 and CO 2 together Upper limit on CO2 Lower limit On Temp If early bacteria produced CH 4 and loved heat. Some bacteria are both methanogens and hypothermophiles f(ch 4 ) = Mixing ratio, mass of CH 4 / mass of air With a stabilizing negative feedback Titan appears orangish due to CH 4 generated aerosols in its atmosphere (like Earth s horizon sometimes from smog) CH 4 makes long organic chains (gas-to-aerosol transformation) that scatter red light CH 4 gas absorbs red light - In large quantity heating up atmosphere instead of surface! Anti-greenhouse gas Earth s climate was not always warm in the past Major partial glaciations: Huronian (2.2.4 b.y.), Ordovician (440 m.y.), etc Complete glaciation: Snowball Earth - Neoproterozoic 600-800 b.y. Ice covered entire planet - mandatory to get out of it plus best observational evidence requires it Ice cut off weathering but didn t stop volcanoes, so CO 2 built up to enormous levels over ~10 million years Snowball Earth continued Gigantic greenhouse effect starts to melt ice Positive ice-albedo feedback melts ice in a hurry, leaving Earth in a super greenhouse state without ice Massive weathering takes Ca 2+ to the ocean where it precipitates and settles. In shallow regions ~400 m deep layer overlies materials freshly deposited by glaciation, this is known as a cap carbonate Evidence from cap carbonates, BIFs (banded iron formations), and glacial deposits 3
So you believe in Snowball Earth now. How did it happen? Something perturbs Earth s temperature substantially below normal Polar sea ice advances and positive feedback ensues Once some high portion of the globe is ice covered, ice expands rapidly due to a climate instability Positive temperature-ice-albedo feedback exceeds the negative temperature-ir feedback giving net positive feedback Continents were in the tropics, so weathering carries on Something special happens when ice reaches midlatitudes So what? Ice covering the planet is cool Rapid melt warmed Earth ~100 C in a thousand years How did Eukaria (our relatives) survived these Events? Snowball Earth Events Eukaryotes Prokaryotic Bacteria 11 animal phyla emerge Two possibilities that caused life to diversify: 1. Isolations of populations in hot springs allowed for genetic mutations and produced new species (recall odd species exist on small, isolated islands) 2. Maybe hardship and rapidly changing environment favored emergence of new life forms 3,500 2,000 800 540 0 Time in millions of years Temperature/Precipitation History So maybe life can survive on ice-house planet We have other evidence that the planet was icefree: Absence of glacial deposits Sedimentary (carbonate) rocks and their Carbon isotopes Absence of BIFs - deep ocean had oxygen Paleosols Redbeds etc 4
Glaciations were just blips - deep past was mostly warm Although Ordovician (440 m.y.) and Permian (250 m.y.) ended with partial glaciations Why? Continents in the polar regions Comet/asteroid impact Volcanism Warm Mesozoic (250-65 m.y.) Dinosaurs - 6 deg C warmer globally Poles were especially warm - mystery Evidence: Lush ferns and alligators in Siberia Carbon isotopes in ocean sediments Higher CO 2 Sea-floor spreading rate was higher Cenozoic - 65 m.y. to present Earth slowly cooled Life retreats from poles Polar ice caps established Most recent ice-ages begin Himalayas form when India collides with Asia Silicate weathering increases Draws down CO2 Eocene ~50 m.y. (recall Dr Battisti s lecture) Extremely warm in the high latitudes Evidence: Crocodiles and redwood trees in the Arctic needed 20 deg C warmer at the poles! CO 2 Clouds in the stratosphere Cause for future concern? end of last ice-age beginning of modern era of ice-ages asteroid impact; end of dinosaurs Cambrian explosion of life; beginning of fossil record Earth freezes over; life survives in pockets rise of atmospheric oxygen life! (prokaryotic bacteria) formation of Earth Geological Time: Fig 8-11 1. Origin of Earth 2. Origin of Life 3. Rise of Oxygen to ~ modern levels 4. Snowball Earth events 5. Beginning of fossil record (Cambrian explosion) 6. Extinction of Dinosaurs by asteroid 7. Beginning of modern glaciations 8. End of last ice-age 4.6 billion ybp (years before present) ~4 billion ybp ~2 billion ybp 600-900 million ybp 540 million ybp 65 million ybp 3 million ybp 10 thousand ybp 5