ATOC 1060 1nd EditionBased on Chapter 11 Lecture 15 Outline of Last Lecture I. Geologic TimeII. Radiometric age datingIII. Solar system formationIV. Formation of EarthV. Atmosphere/Ocean formationVI. Composition and climate of Early EarthOutline of Current Lecture I. Earliest life formsII. Preserved in RocksIII. OxygenA. Abundance B. EvolutionC. Are they higher/ lower than todayCurrent LectureI. Earliest life forms- 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. These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.What did the earliest life forms on our planet look like? How did they get energy? - 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 AtmosphereTwo types of photosynthesis Cyanobacteria: First photosynthetic organismsToday – Cyanobacteria perform anoxygenic and oxygenic photosynthesis depending on their environment. Are lipids/steranesin rocks ~2.6 bya are evidence for cyanobacteria, oxygenic photosynthesis, and O2?II. 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. Anoxygenic= photosynthesis WITHOUT oxygen producedHydrogen (H2) or Hydrogen Sulfide (H2S) used to reduce COOxygenic= photosynthesis WITH oxygenproducedH2O used to reduce CO2What 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 III.III. OxygenWhen atmosphere Oxygen increased, Ozone Rise, Same time as rise in Oxygen (~2.4 b.y.a.) First multi-cellular Life Multicelled organisms delayed by low O2until about 560 m.yEdiacaran fauna – flattened bodies designed to maximize surface uptake of oxygen, Still lower O2 than present Cambrian ExplosionWe still get lots of power from the coal deposits that formed during this time. This is how the Carboniferous Period got its name (around ~300 million years ago)The carbonate (inorganic) isotope data is used to infer past O2 by using our knowledge of these processes -Less Oxygen implies higher C:P ratios and more organic carbon burial. -More organic carbon burial leads to more Oxygen. -THIS NEGATIVE FEEDBACK HELPS MAINTAIN STABLE OXYGEN IN OUR