ATOC 1060 1nd EditionExam # 1 Study Guide Lectures: 12-19Lecture 12-13 Carbon Cycle Difference between organic and inorganic carbonOrganic: is alive, works on human times scalesInorganic: dead, works on geological (very long) timescalesSome parts of organic cycle also work on long timescalesShort term terrestrial organic carbon cycle (photosynthesis, respiration, decomposition)Photosynthesis: Process by which plants use sunlight to take up CO2 produce energy and release O2Respiration: process in which energy and O2 are used and C02 is releasedReturning carbonRespiration: returns 1/2 that was taken up by photosynthesisDecomposition in Soil: returns 1/2 Methanogenesis: methane reacts with O2 to form CO2Decomposition is accelerated in warm environments, so if the Earth warms up, rates of decomposition will increase. This will add more CO2 to the atmosphere, which will increase surface temperaturesBiological pumpBiological pump: Organic matter that reaches the seafloor is deposited as sedimentComponents of the inorganic carbon cycle Weathered Carbon goes into the ocean and contributes to marine inorganic carbon cycleMarine inorganic carbon cycle has the largest reservoir: limestoneThe ocean is very important for removing CO2 from the atmospherePhysical/mechanical weathering: rocks break down by physical processes, such as ice growth, wind or sand erosion, plant growth, heat stress Chemical weathering: rocks break down by exposure to chemicals, such as acid rainLecture 14 Formations of Solar System/Earth and Early Earth ClimateRadioactive isotopesUnstable isotopes decay to become stable isotopes at a known exponential rate.Half Life = time when 50% of the material has decayed.Carbon 14 dating and lead Solar System formation- 4.55 billion years ago Our solar system formed 4.6 billion years ago when an interstellar cloud collapsed! - Gravitational collapse of an interstellar cloud to form the solar nebula - The rotation rate of a nebula dictates how many stars are formed. - Faster rotation=more stars. In our case, one star formed (the sun) and planets formed in the disk around it.Earth FormationThe solar system/Earth formed 4.55 billion years ago Formed during the Heavy bombardment periodFormed by Accretion in ~100 million years- Planetesimals formed as condensed materials attracted to the mid-plane of nebula. Planets formed by the accretion (‘sticky collisions’) of planetesimals- Craters on Mars, Mercury, and Moon provide good evidence for the Heavy bombardment periodAtmosphere and Oceans FormationAtmosphere and oceans began forming as Earth itself formed during the Heavy bombardment period (4.6-3.8 billion years ago) Impact degassing: bombardment of Planetismals releasing water and other volatile compoundsComposition and climate of the Earth’s early atmospherePlenty of nitrogen (N2) since impactors brought Ammonia (NH3) - Likely that there was CO2. Impacts released the reduced gases CO and CH4, which can turn irreversibly into CO2- Very little oxygen (O2) because: 1) no photosynthetic biology 2) O2 reacts quickly with CH4and CO to form CO2Lecture 15 Effect of Life on the Atmosphere/History of OxygenEarliest Life Forms (methanogens, cyanobacteria)- Our atmosphere was likely formed from impact degassing during the heavy bombardment period (~3.8 – 4.55 bya) - Nitrogen N2 (formed from NH3rich impactors) and Carbon Dioxide CO2(formed from irreversible oxidation of CO and CH4) were likely present. O2was not (reduced atmosphere).- Life likely originated in first 700 my of Earth history, as shown by microfossils. Life impliesliquid water was present. - First organisms likely chemosynthetic (energy produced by chemical reactions). - Likely chemosynthetic methanogen bacteria. - Note: Methanogens cannot live around oxygen. Methanogens consistent with reduced early Earth atmosphere. - Stromatolites (3.5 b.y.a) = Fossilized remains of bacteria, Layered sedimentary mats - Stromatolites were likely photosynthetic, but probably by an oxygenic photosynthesis - No Oxygen in Early Earth AtmosphereEvidence of life been preserved in rocksRust is a very common, reddish-brown iron oxide. Iron oxide is formed when iron and oxygen react in the presence of water or moisture in the air. Rust requires oxygen. What are Banded Iron Formations (BIF)- Laminated sedimentary rocks that consist of alternating, millimeters-thick layers of iron-rich minerals and chert- Important source of iron for steel (your car!) - Almost all formed prior to 2.4 b.y ago. - Implication = early oceans had little oxygen, which allowed for build-up of Fe2+ in the water Cambrian ExplosionLecture 16-17 Long term Climate RegulationFaint Young Sun Paradox and ResolutionFaint Young Sun Paradox is how we explain a warm early earth.- Less incoming solar radiation when Earth formed 4.6 billion years ago. - Large greenhouse gas concentrations (likely methane) provide warmth on early Earth. Sun was 30% dimmer when earth formed yet there was liquid waterThe solutions to the Faint Young Sun Paradox?- The greenhouse effect was higher Methane and CO2- Not water vapor which is closer to saturation and provides a positive feedback not a long term forcing- The Planet albedo was Not lower in the past- Geothermal Heat was NOT big enough to supply the required energyEarly Earth like Daisyworld. stable and unstable equilibria What are processes explaining the couplings? (Focus on Figure12-6).Climate During Snowball Earth?Snowball Earth: There were glaciers in the tropics and the entire earth was frozenThere were 6 major glaciation periods over Earths HistoryHow did we “escape” Snowball Earth to a warmer climate?A. methane emissions from methanogens living in the ocean increasesB. carbon dioxide increases no sink from silicate C. positive ice albedo feedback and positive water vapor feed backD. all the above E. B and CWarm Mesozoic Climate Evidence- Fossil record: Ferns and gators in Siberia, Dinosaur skeletons found north of Arctic Circle - Oxygen isotopes: deep ocean warmer than present (+2K), polar ice caps were absent No ice caps = Higher sea level =probably no sea ice4x today’s atmospheric CO2levels could explain Warm Mesozoic During the Eocene (~50 million years ago)Eocene (~50 million years ago) CO2 ~1000 ppm was Super war1. Faster spreading rates Faster Subduction of carbonate sediments More carbonate metamorphism More atmospheric CO2 (enhanced CO2