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It is important to study the early climate of Earth as it was a factor on how life evolved, what type of life evolved and the rate of this evolution. It had profound effects on the state of the atmosphere and the rock record which captures much of this information
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See Graedel and Crutzen
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I don’t think anyone was around or thermometers were invented Millions of years ago to measure the weather and climate of the past
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Paleo is derived from the Greek word for ancient, palaios
Paleoclimatology is the science that helps us reconstruct past climates. We must find things old that may bear a temperature signature. If they are in sediments or cores we must age them, then we have to extract information that may reflect the temperature
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Proxies are all we have. Relationships between known physical or chemical relationships that tie to temperature. Isotopes have discrimination during temperature dependent processes like enzyme kinetics, diffusion, evaporation and condensation. Linking these to the biomass of old dead and preserved fossils provides a means to deduce temperature.
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http://www.geomore.com/wp‐content/uploads/2012/04/oil‐and‐gas‐traps‐microfossil.jpg
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Corals can also provide information on paleo‐climate
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Belmecheri, S., F. Babst, E. R. Wahl, D. W. Stahle, and V. Trouet. 2015. Multi‐century evaluation of Sierra Nevada snowpack. Nature Clim. Change advance online publication.
This record of snow in the Sierras is based on 1300 tree rings from blue oaks in the foothills. See testing and fitting and them extrapolation
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There is fractionation between heavier and lighter isotopes through such processeslike diffusion, chemical reactions, evaporation and condensation. Very precise mass spectrometers can measure isotope ratios and infer past climates with various interpretations
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We can age rocks by looking at the ratio between lead and uranium. The non linear relation tells us it is better at detecting ages of rocks more than 500 million years old.
http://www.uwgb.edu/dutchs/Petrology/RadDateUTh.HTM
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Radioactive carbon 14 dating is used to find how old organic material may be
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Oxygen isotopes and the ratio of magnesium to calcium provide some information on temperature that is widely used.
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https://iso‐net.atlassian.net/wiki/download/attachments/1245194/image2014‐3‐18%2011%3A52%3A20.png?version=1&modificationDate=1395139979261&api=v2
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The isotopic value of 18O in rainwater has been found to correlate well with temperature. So temperatures can be reconstructed from ice cores.
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http://www.geo.hunter.cuny.edu/tbw/wc.notes/14.climate.change/Lab.Related/warm.cold.climate.isotope_cycle.jpgIn a warm climate evaporation prefers the lighter water isotope, leaving the bulk water isotopically heavier. The heavier isotope is preferred during condensation, so runoff back to the ocean is isotopically heavier than the vapor, but still lighter than the source water.
When it is cold and ice is formed this condensed water is trapped as snow and ice, causing ocean water to become progressively heavier.
and the future rain isotopically lighter. Vice versa for cold climates
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http://web.sahra.arizona.edu/programs/isotopes/images/diagram13.gif
Evaporation favors water with the lighter isotope, 16O, causing the d18O value of vapor to be more negative than ocean water.Condensation favors the heavier isotope, so the d18O of rain is less negative than vapor
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This is an imperfect thermometer with non linear features and scatter.
Anand, P., H. Elderfield, and M. H. Conte. 2003. Calibration of Mg/Ca thermometry in planktonic foraminifera from a sediment trap time series. Paleoceanography 18:n/a‐n/a.
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The past climate has not always been steady and has changed back and forth between hot house planet, an ice covered planet and a mild and benign state, as we have had until recently
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Kasting, J. F. and D. Catling. 2003. Evolution of a habitable planet. Annual Review of Astronomy and Astrophysics 41:429‐463.
Why is Venus too hot, Mars too cold, and Earth "just right" for life? (The allusion to the fairy tale involves the three bowls of porridge belonging to Papa Bear, Mama Bear, and Baby Bear‐one too hot, one too cold, and one just right‐tested by a hungry Goldilocks.) A simplistic answer might be that a planet's surface temperature is to a large extent a function of its distance from the Sun, and Earth just happens to be at the "right" distance for comfortable temperatures and liquid water. However, this is far from the whole story.
The advanced student may ask why did this plot imply that the Earth was Frozen before 2 Ga? Good question. The simulations on which these computations were based erroneously assumed CO2 equaled 300 ppm,
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Kasting, J. F. and D. Catling. 2003. Evolution of a habitable planet. Annual Review of Astronomy and Astrophysics 41:429‐463.
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See Kasting and CatlingEvidence
Iron Rich Rocks Near Tropics, form in low oxygen oceans
Dirt and Debris left behind when Ice Melted
Life survived near hot springs or by cold loving microbes
Was reversible by CO2
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In the early years, Earth was a huge snow ball. What effect would this have on evolving life, the state of the land and air? What ended it
http://creationrevolution.com/wp‐content/uploads/2013/09/snowball‐earth.jpg
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Kasting and Catling
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First Question Why Us? Why is Earth the planet with an ideal climate to host life, and not Venus or Mars. All can be considered to be in a habitable zone, with regards to the Sun.
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The size of the planet, its distance from the Sun and the type of its atmosphere play big roles whether or not liquid water can exist on a planet, the first requirement for Life. Venus is close to the sun but the clouds are very bright, giving it a high albedo (76%). So despite the largest solar constant its effective radiative temperature is only 229K. Earth is next from the sun. With a lower albedo (30%), its radiative temperature is 255K, much below the freezing level of 273 K. Mars, the farthest and smallest, has a thin atmosphere, relatively low albedo and a low solar constant. Together these yield a radiative temperature
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An early interpretation of the runaway greenhouse effect. The dashed curves showhow surface temperatures increase, due to the greenhouse effect, as water vapor accumulates inthe atmospheres of Venus, Earth, and Mars. On Mars and Earth, the increase is halted when thewater vapor pressure is equal to the saturation vapor pressure, and either freezing or condensationoccurs. Temperatures on Venus are higher because Venus is closer to the Sun, and saturation isnever achieved. Therefore, temperature runs away. Remember water vapor is a strong greenhouse gas, which absorbs infrared radiation effectively and re –radiates it to the surface. Also because there was no liquid water on Venus, weathering could not occur and act as a sink and negative feedback on the CO2 effect
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Homeostasis or homoeostasis (homeo‐ + ‐stasis) is the property of a system in which variables are regulated so that internal conditions remain stable and relatively constant.
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http://d32ogoqmya1dw8.cloudfront.net/images/introgeo/models/Daisy3.jpg
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Literal Gaia has been subject to many papers and conferences and has been rejected due to lack of evidence. There is general acceptance of a weak Gaia. If anything Gaia has been influential in being thought provoking and introducing Biology into our search for understanding the evolution of the chemical composition of our atmosphere and the climate system.
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Life evolved over time across a wide range of climates. Of course this promoted some life forms, caused extinction of others and the system often restarted on a different trajectory when favorable climate resumed. Look at the age of dinosaurs vs dominance by mammals today/https://upload.wikimedia.org/wikipedia/commons/f/f5/All_palaeotemps.png. Original Data sourcesData are shared at http://gergs.net/?attachment_id=1014
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http://www.globalwarmingart.com/wiki/File:Phanerozoic_Climate_Change_Rev_png
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Role of tectonics on climate, but at long and slow time scales Remember issues of scale
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http://www.globalwarmingart.com/wiki/File:65_Myr_Climate_Change_Rev_png
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Early Climate Timeline in a Snapshot. Key points, repeated periods of Snow ball earth and Hot House Earth
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We can study the past biosphere by looking at the composition of air and dust on accumulated layers of ice or lake sediments. Isotopes are important as they serve as proxies for temperature and rain. Direct sampling of air bubbles tell us what was in the air. Counting layers, like growth rings on a tree help us age the cores.
http://earthobservatory.nasa.gov/Features/Paleoclimatology_IceCores/
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http://www.globalwarmingart.com/wiki/File:Ice_Age_Temperature_Rev_png
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Feedbacks between land and ocean sources and sinks for carbon had tight regulation on the maximums and minimums of CO2 between glaciations. Over the past million years and over the course of 9 inter‐glacial periods, CO2 tended to by limited to 280 ppm. In contrast, a floor of about 180 ppm was reached during the peak of glaciations.
The other key point is that CO2 tended to rise ‘rapidly’, over about 10k years between glacial and inter‐glacial conditions. In contrast the decline in CO2 from 280 to 180 ppm from inter‐glacial to glacial conditions tends to be slow and lasts about 100 k years.
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http://www.jamstec.go.jp/e/about/press_release/20141027/img/image002.jpg
http://www.eoearth.org/view/article/154612/
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Raymo and Huybers Nature
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http://www.indiana.edu/~geol105/images/gaia_chapter_4/eccentric.JPGThe strongest time scale of temperature changes is associated with Eccentricity, a cycle that has the smallest impact on solar heating of the Earth. Yet it is expected to initiate or trigger additional feedbacks that amplify the cooling or warming, as with CO2.
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http://www.indiana.edu/~geol105/images/gaia_chapter_4/axial.JPG
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http://www.indiana.edu/~geol105/images/gaia_chapter_4/precess.JPG
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http://math.ucr.edu/home/baez/Milankovitch_Variations.pnghttp://math.ucr.edu/home/baez/week318.html
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The tilt and orbit of the planet and its revolution around the sun and its axis has not been constant. It oscillates with time and this has lead to major climatic shifts between ice ages and inter glacial periods.
Zachos et al Science 2001
http://www.eoearth.org/view/article/154612/http://www.indiana.edu/~geol105/images/gaia_chapter_4/milankovitch.htm
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http://www.wga.hu/art/b/bruegel/pieter_y/birdtrap.jpgWinter landscape with a bird trap
New paper and seminar by Alyssa Atwood, shows the effects of volcanism. Accounts for 40% of the forcing
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Today the Dutch rarely have snow during the winter and frozen canals for ice skating are nearly non existent.
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http://www.globalwarmingart.com/wiki/File:2000_Year_Temperature_Comparison_png
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Some have assumed that there was an association between sunspot activity and the little ice age, but the change in solar output is too little. In sum there is no convincing evidence for a mechanism between sunspots and the little ice age; note onset of little ice began before Minimumhttp://cdn.phys.org/newman/gfx/news/hires/2011/solarcyclepr.jpg
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What Else should we Recall from this set of Lectures
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You can see by these attributes of Gaia, why we frame much of this class on the Biosphere around the concept and topic of Complex systems.
Based on Schrodinger’s idea of Entropy and Life and Lovelock’s Ideas on Gaia is the ‘Biosphere a Living Organism?’
Over time the idea that the Earth is a ‘living organism’, per se has been dismissed. There have been a series of articles critiquing Gaia, defending it, and refining it based on more rigorous scientific logic.
S. Schneider and P. Boston (eds) Scientists on Gaia. 1993. MIT Press
Kirchner, J. W. (2002), The Gaia hypothesis: Fact, theory, and wishful thinking, Clim. Change, 52(4), 391‐408.
Lenton, T. M. (2002), Testing Gaia: The effect of life on Earth's habitability and regulation, Clim. Change, 52(4), 409‐422.
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