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2 Middle-aged Sun 4.6 Billion years old

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4 The Faint Young Sun Paradox. Solid line is solar luminosity relative to present (S/S0). Ts is Earth’s surface temperature and Te is Earth’s effective radiating temperature. Thick vertical bars are glaciations. SOURCE: Modified from Kasting and Catling (2003). A faint young sun ~4 billion years ago the sun was 70% as luminous as today

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7 The Faint Young Sun Paradox. Solid line is solar luminosity relative to present (S/S0). Ts is Earth’s surface temperature and Te is Earth’s effective radiating temperature. Thick vertical bars are glaciations. SOURCE: Modified from Kasting and Catling (2003). Less solar radiation (70 W/m 2 ) so Earth should be frozen, BUT it wasn’t!

8 The Faint Young Sun Paradox. Solid line is solar luminosity relative to present (S/S0). Ts is Earth’s surface temperature and Te is Earth’s effective radiating temperature. Thick vertical bars are glaciations. SOURCE: Modified from Kasting and Catling (2003). Less solar radiation (70 W/m 2 less) so Earth should be frozen, BUT it wasn’t! What compensated for the Weak radiation (heat)?

9 The Faint Young Sun Paradox. Solid line is solar luminosity relative to present (S/S0). Ts is Earth’s surface temperature and Te is Earth’s effective radiating temperature. Thick vertical bars are glaciations. SOURCE: Modified from Kasting and Catling (2003). Less solar radiation (70 W/m 2 less) so Earth should be frozen, BUT it wasn’t! What compensated for the Weak radiation (heat)? Compensation ONCompensation OFF

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12 Heat from below – Geothermal heat

13 Heat from below – Geothermal heat 0.3 W/m 2 more heat…. Not enough to make up for 70 W/m 2 less solar heat. Maybe enough to keep the deep ocean from freezing.

14 What about albedo? Was it much lower in Earth’s early history?

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16 Redistribute the Carbon – put more Carbon in atm

17 Super greenhouse world

18 Super greenhouse world But where did all the atm CO2 go?

19 So where did the CO 2 come from that isn’t still supplying it at the same rate today?

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21 So early Earth had more volcanic outgassing. Why didn’t the CO2 that was emitted early on just build up in atm? Must be more to the story…. Is anything removing the atm CO2 that didn’t before? Carbon in the Earth

22 Super greenhouse world Earliest life

23 Super greenhouse world Earliest life

24 Once the continents are built then they can be chemically weathered – this removes atm CO 2

25 Long Term Climate Thermostat = Chemical weathering of continents What type of feedback is this?

26 So volcanic outgassing was the main input of CO 2 in early Earth and chemical weathering was the main drawdown of atm CO 2. limestones

27 The Faint Young Sun Paradox. Solid line is solar luminosity relative to present (S/S0). Ts is Earth’s surface temperature and Te is Earth’s effective radiating temperature. Thick vertical bars are glaciations. SOURCE: Modified from Kasting and Catling (2003).

28 What about life? What role did it play in atmospheric evolution of Earth?

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