Environmental Chemistry

Origins Create the universe Create the elements Create the Earth Form the atmosphere and oceans

Carbonate-silicate cycle Timescale = 105 – 107 yrs J. F. Kasting, Science Spectra, 1995

Feedback on CO2 Figure 09-11 How to Build a Habitable Planet Copyright © Princeton University Press 2012

Historical CO2 record from Berner, Science, 1997

Solar output over time Solar output has increased by ~30% Figure 09-09 How to Build a Habitable Planet Copyright © Princeton University Press 2012

What about oxygen?

Oxidation states of elements Figure 15-02 How to Build a Habitable Planet Copyright © Princeton University Press 2012

Step 1: Autotrophs E.g., Purple sulfur bacteria 6 CO2 + 6 H2S + light  C6H12O6 + 6 S Uses energy from light Oxidizes S and reduces C

Respiration Metabolizes glucose to produce ATP, CO2, and water Anaerobic respiration (no O2) produces 2 ATP per glucose C6H12O6  2 CH3CH2OH + 2 CO2 2ADP 2ATP

Step 2: Oxygenic Photosynthesis Uses solar energy to split water and form organic compounds O2 is a by-product

Step 3: Aerobic respiration Uses free O2 to oxidize organic matter Generates 36 ATPs Provides enough energy for complex organisms

Oxygen is consumed by reactions with reduced Fe and S from lithosphere

Banded iron formations

“Biogeochemical cycle modelling indicates that prolonged super- greenhouse conditions and effective nutrient input to the ocean after the glaciation lead to high levels of primary productivity and burial of organic carbon. This causes an abrupt jump of oxygen levels within ∼104yr after the glaciation and an extensive oxygen overshoot to the present atmospheric level. The overshoot persists for ∼108yr because net consumption of oxygen in the atmosphere–ocean system is inefficient. We show that the post-glacial jump of oxygen levels occurred in biologically short timescale, which may have stimulated the ecological shift and/or biological innovations toward the prosperity of oxygen-dependent life.”

Evolution of life

Coevolution of CO2 and O2 http://www.chegg.com

Carbon cycle Cycle includes flows of carbon from photosynthesis and respiration as well as Ca-Si cycling

Nitrogen Cycle Processes