ATOC 1060 1nd EditionBased on Chapter 12 Lecture 17 Outline of Last Lecture I. Burying CarbonII. Carbon Cycle during Carboniferous PeriodIII. Faint Young Sun ParadoxSun was dimmer back thenIV. Snowball Earth long term climate change our planet was covered with glaciersOutline of Current Lecture I. Review Early Climate/ Snowball EarthII. Atmospheric Carbon Dioxide and ClimateIII. Mesozoic/Eocene warm climates IV. Cooling of the Cenozoic Current LectureI. Review Early Climate/ Snowball Earth-Over the last 4 billion years, the sun has been getting brighter -Important on long-term timescales – Not on human timescales! Faint Young Sun Paradox: 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. Long-term climate changeThese 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.Although Earth ‘stable enough’ to support life since ~3.8b.y.a, the climate record shows long-term climate change..Interglacial periods = Earth warm. On average, Earth has been warm more often than cold.Glacial period = Earth cold, extensive ice caps present. Evidence for 6 major glacial periods, including Snowball EarthHuronian Glaciation - Rise of O2 around 2.4 b.y ago would have eliminated most of the methane. And created a Snowball EarthII. Atmospheric Carbon Dioxide and ClimateCO2 drives climate variations during the Phanerozoic (544 million years ago to- Cool Carboniferous/Permian (~300 m.y.a.) - Warm Triassic-Eocene (251-34 m.y.a.) - Cooling/cool ever since (34 m.y.a. to present) III. Mesozoic/Eocene Warm Climates Mesozoic = Warmer than todayEvidence?- 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 Why more atmospheric CO2? 1. Faster spreading rates Faster Subduction of carbonate sediments More carbonate metamorphism More atmospheric CO2 (enhanced CO2 source) 2. Higher sea level Less exposed land Less silicate weathering (reduced CO2 sink)Eocene (~50 million years ago) CO2 ~1000 ppm was Super warIV. Cooling of the Cenozoic Accelerated cooling 30 million years