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Paleoclimate History of Earth Climate

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Paleoclimate History of Earth Climate Paleoclimate History of Earth Climate Stromatolites, the dominant fossil type for the later part of the Precambrian period. Geological Epochs Ice Worlds Inorgancic Carbon Cycles Continental Drift Water Worlds The Gran Canyon imprint of Earth’s Geological & climate history 65-0Ma 248-65Ma 543-248Ma Eukaryotes 4500Ma-543Ma Geological Periods Temperature of Earth in the Precambrian The initial period (Hadean period) after the formation of Earth 4 billion years ago was characterized by a hot, very active volcanic environment, which was further impacted by steady bombardment of asteroids from the formation process of the solar system. There was a slow cooling for the first 3 billion years. The solar flux F was 20% - 30% smaller in comparison to today due to the initially lower solar energy production. This and the lack of an appreciable atmosphere related absorption effect may have caused cooling well below the present temperatures with subsequent glaciation of the entire earth surface. This idea is named snowball earth model and is supported by the existence of glacial deposits and glacial strata worldwide, also near the paleo-equator regions. Isotope abundance and long-lived radioisotope data are the proxies for testing these predictions. Radiation loss at high surface temperatures 5.00E+08 At higher temperatures the CO2 T=700oC absorption band at 15m is too 4.50E+08 far removed from emission 4.00E+08 spectrum and the efficiency of 3.50E+08 the absorption and greenhouse T=300oC 3.00E+08 role of CO2 is diminished. F() CO2 absorption band 2.50E+08 14 12 2.00E+08 m] [ 10 1.50E+08 8 6 1.00E+08 T=20oC 4 5.00E+07 o Wavelength Wavelength 2 T=-20 C 0 0.00E+00 -50 150 350 550 750 950 1.00E-06 6.00E-06 1.10E-05 1.60E-05 2.10E-05 2.60E-05 3.10E-05 3.60E-05 Temperature [oC] Wavelength [m] Shift of the maximum value F()max of Rapid cooling enhances the efficiency of the Planck spectrum with temperature T. heat absorption and triggers warming effect if CO2 is present in the atmosphere. De-icing of earth is difficult because the albedo of an ice-covered earth, ≈0.8 is significantly higher than the albedo of brown earth, ≈0.3 leading to a further reduction of solar heating, because 80% (instead of 30%) of the flux is reflected. Temperature increase occurs through slow generation and growing efficiency of CO2 green house gases. High volcanic activity continues to produce CO2, which is absorbed in the Precambrian ocean. This causes a decline in CO2 and Earth cooling. Glaciation prevents CO2 absorption! The absence of the ocean as CO2 sink causes a slow build-up of a greenhouse gas atmosphere. This leads to a gradual increase in temperature up to 50oC causing a rapid melting of the ice sheet and triggering a new warm period. The inorganic carbon cycle in a Precambrian world Heating and cooling of the earth temperature in the late Precambrian period depends on the slow variation of the atmospheric CO2 content. An overabundance of CO2 leads to warming because of the greenhouse effect, an lower abundance of CO2 will lead to lower temperature because of the increased radiation loss through earth’s atmosphere. The CO2 plays an increasingly efficient role with the cooling of the earth surface, with the slow build-up at first. A CO2 equilibrium is eventually established through the inorganic carbon cycle, which is much slower than the organic or biological carbon cycle, which controls the CO2 balance today. William Ruddiman, Earth’s Climate, W.H. Freeman & Co New York, 2008 The CO2 balance in the Precambrian world is driven by carbon chemistry between CO2 gases released from hot magma or tectonic shifts and the CO2 absorption by the rock environment through weathering (converting limestone to quartz). In the oceanic marine environment CO2 is initially released by limestone dissolution until the build-up of marine flora. S: sedimentation M: metamorphosis W: weathering CaSiO3 CO2 CaCO3 SiO2 Limestone and quartz formation MgSiO3 CO2 MgCO3 SiO2 CO2 H2O H2CO3 Limestone dissolution in water CaCO3 H2CO3 CaCO3 CO2 Carbon cycle and vapor feedback chemical weathering as earth’s thermostat Different feedback mechanisms balance the climate development over tectonic timescales, the best example is the inorganic carbon cycle ! CO2 CO2 Alternative feedback mechanisms, e.g. formation of water vapor lead to a feedback driven amplification of the initial climate disturbing H2O effect. This could cause climate oscillations through coupling with other feedback processes. Snowball model with The occurrence of a hot phase subsequent hot phase is supported by the 18O isotope fractionation in the FeO (II), FeO(III) banded iron formations and 18O and 13C fractionations in carbonates. A. Heimann et al. Earth & Planetary Sci. Lett. 294 (2010) 8-18 18 0 O 21 0.675T 0 15 00 C 2115 0 T 0 53 C C 0.675 CO2 concentration and temperature fluctuation o CO2 T( C) 5000 ppm 20oC 3000 ppm 10oC 1000 ppm From Oxygen-poor to Oxygen-rich Three interrelated developments cause an increase in atmospheric O2 concentrations about 2.4 Ma ago (measured from FeO2 to FeO3 ratios) • organisms began to convert atmospheric nitrogen (N2) into more complex molecules triggering the formation of plant life forms, • an ozone layer shield developed, which prevents DNA-disrupting UV radiation from reaching the earth surface, • oxygen-carbon photosynthesis, or the organic CO2 cycle converting water and CO2 into sugar & oxygen starts operating. Additional factors causing an O2 enriched atmosphere include changes in the chemistry of volcanic gasses, more volcanoes erupting on land than under the ocean, the escape of hydrogen into space, the development of continental Earth corona is due to masses that sequester carbon, and an solar light scattering on overall decline in volcanic activity. escaping H2 molecules! The Oxygen development as trigger of biological life, reducing CO2 content The Cambrian explosion 545Ma BP refers to a rapid evolution of life forms based on the fossil records. Snowball Earth, 2.3 billion years ago Occurrence of snowball earth in 700 million years ago later periods requires removal of 480 million years ago CO2 from the atmosphere to interrupt the CO2 equilibrium !?! 300 million years ago Atmospheric CO2 material is about 600 Gt (Gigatons), natural annual removal process is about 0.15 Gt. M 600Gt t CO2 4000yr M 0.15Gt yr CO2 Rapid removal or release of CO2 could trigger fast (on geological time scale) climate changes. Major disturbances in early earth history are tectonic motions! Time (million years) Time (million years) Tectonic plates and rapid climate change Nuna (Columbia) 2.8 Gy ago Rodinia 1.1 Gy ago Pannotia 0.5 Gy ago Pangaea 0.3 Gy ago Gondwana et al. <0.3 Gy ago towards continents today Tectonic shifts can release more CO2 through enhanced volcanic activity. It can also reduce CO2 through a polar versus equatorial position of continents or sea-floor spreading and CO2 burial through rapid organic CO2 absorption in times of expansion of tropical flora, which would reduce the CO2 greenhouse effect. Other reasons may be changes of atmospheric circulation by mountain formation and change in ocean currents by changes in land sea location. The continental shelves today Paleo-Continental distributions Nuna/Columbia 2000 Ma Rodinia 1000 Ma Ice world? Pangaea 200 Ma Gondwana 100 Ma Desert or tropical world! Correlation between CO2 and O2 level Imbalances in the atmospheric CO2 level correlates with the O2 level in the atmosphere since both are coupled through the organic CO2 cycle . Pangaea Pannotia Snowball world Low CO2 levels indicate cold ice age like periods, high CO2 levels suggests hot periods with little CO2 absorption. High O2 levels indicates high flora levels ! Atmosphere Ocean Coupling in Pangaea Climate model simulations for Pangaea predict extreme aridity in the interior of the continent, with low annual precipitation except for the coastal areas, which are predicted to have higher soil moisture. These predictions are confirmed by analysis of Pangean salt deposits, which are substantially larger than for other periods, indicating dry climates. The hot summers prevented the build up of ice sheets on the poles despite the cold winters in the Northern hemisphere. High pressure zone directs wind (and snowfall) toward southern regions and ocean. Earth in the Cretaceous Period a greenhouse world 100 million years ago Pangaea was drifting apart, growing CO2 levels cause green house effect preventing the build up of polar ice shelves. Considerably higher sea levels (~200m), shallow sea areas with rich marine life. High humidity and precipitation due to multi-coastal areas. The cretaceous period was characterized by high CO2 concentration (~5 times pre-industrial concentrations) in the atmosphere. The average temperature was about 10oC to 25oC higher than today. An additional component was the reduction of albedo due to the increase in ocean area and the increased efficiency of tropical heat distribution through a rather complex ocean current system between continental islands. Towards the end of the cretaceous period cooling occurred, probably associated with changes in the landmass distribution and uplifting of mountains (Himalaya and Rocky Mountains), which changed the global wind circulation patterns. Ocean currents in the Cretaceous period Early cretaceous period Pre-cretaceous current pattern prior to the break up of Pangaea Late cretaceous period Critical gates and passages for ocean currents End with a Bang - 65Ma ago Chicxulub or the KT extinction event .
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