Constraining crustal silica on ancient Earth
C Brenhin Keller1, T Mark Harrison2
1Department of Earth Sciences, Dartmouth College, Hanover, NH 03755; cbkeller@dartmouth.edu tmark.harrison@gmail.com.
Summary
Early Earth
Area of Science:
- Geoscience
- Planetary Science
- Earth Science
Background:
- Understanding Hadean and Archean Earth's continental crust composition is crucial for early life and planetary evolution.
- Previous models proposed either a mafic crust with limited plate tectonics or a more uniformitarian crust composition.
- Crustal preservation biases and secular cooling effects complicate compositional analysis.
Purpose of the Study:
- To accurately quantify the composition of Hadean and Archean continental crust.
- To investigate the impact of mantle cooling and atmospheric oxidation on crustal composition estimates.
- To reconcile conflicting models of early Earth's crustal evolution.
Main Methods:
- Analysis of geological data, considering crustal preservation and sampling biases.
- Modeling the effects of secular mantle cooling on element abundance inferences.
- Assessing the influence of atmospheric oxidation on sedimentary proxies for crustal silica.
Main Results:
- Secular mantle cooling complicates inferences of crustal silica from element abundances.
- Biologically driven atmospheric oxidation undermines silica estimates from terrigenous sediments.
- The data are best explained by a model of nearly constant crustal silica since the early Archean.
Conclusions:
- Early Earth's continental crust composition has been relatively consistent since the early Archean.
- Previous models may have underestimated crustal silica due to unconsidered environmental factors.
- This finding has significant implications for understanding early Earth's tectonics, climate, and habitability.
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