Oxidation of the Earth's Surface Flashcards
Why is direct measurement of past atmospheric oxygen (O2) impossible?
Oxygen levels must be inferred from examining elements and reactions that reflect and control oxidation states.
Which elements play crucial roles in reflecting and controlling Earth’s oxidation state?
Carbon (C), Iron (Fe), Sulphur (S), and Hydrogen (H).
What processes liberate and consume oxygen on Earth?
Photosynthesis liberates oxygen.
Processes like organic matter breakdown, heterotroph consumption, and burning consume oxygen.
How does Earth’s interior contribute to the oxidation state?
It is relatively reduced, with magmas and gases carrying reduced species to the surface, while rock weathering contributes to oxidation.
What maintains present-day O2 levels at around 21%?
The balance between sources (photosynthesis) and sinks (aerobic respiration, mineral oxidation), and feedback mechanisms.
How do carbon isotopes help track oxygen production over time?
Differences in carbon isotope ratios (d13C) between organic and inorganic carbon allow estimates of the proportion of organic to inorganic carbon.
What challenges exist in using the carbon isotope record to study ancient oxygen levels?
Scarcity and alteration of organic matter in the geological record, and difficulties in correlating data from different locations.
What are Banded Iron Formations (BIFs), and why are they significant?
BIFs consist of alternating layers of iron-rich sediments and cherts, peaking around 2.5 billion years ago, and indicate transitional oxygen levels.
How do sulphur isotopes provide insights into the early rise of oxygen?
Variations in Mass Independent Fractionation (MIF) of sulphur isotopes indicate low atmospheric ozone levels and low oxygen levels before 2 billion years ago.
What is the “Great Oxidation Event”?
The period around 2.2 billion years ago when atmospheric oxygen levels significantly rose, indicated by transitions in paleosols.
What factors could contribute to the rise in oxygen from 2.0 Ga to 0.6 Ga?
Increasing sources like organic carbon burial and decreasing sinks such as subduction of organic carbon and oxidation of continental rocks.
What evidence suggests high oxygen levels during the Phanerozoic?
Red beds, fossil evidence, modelling, carbon isotope data, and gypsum in evaporites.
How does the global oxygen mass balance relate to organic matter formation and oxidation?
The balance between electron addition through organic matter formation and electron subtraction through oxidized compounds must be maintained.
What role does hydrogen loss to outer space play in Earth’s oxidation?
Hydrogen loss, possibly through methane formation, may create a reduced reservoir and contribute to the global mass balance, aiding oxidation.
Why is methane significant in early Earth’s atmosphere?
Methane may have contributed to a greenhouse effect, keeping Earth warm, and its loss through ionizing radiation could help create an electron flux aiding oxidation.
