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Updated: Aug 17, 2025
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Simulation of Early Earth Hydrothermal Chimneys in a Thermal Gradient Environment
Published on: February 27, 2021
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Chert oxygen isotope ratios are driven by Earth's thermal evolution
M Tatzel1,2, P J Frings2,3, M Oelze2,4
1Department of Sedimentology and Environmental Geology, Geoscience Center Georg-August-Universität Göttingen, 37077 Göttingen, Germany.
Summary
The oxygen isotope ratio in cherts (δ18Ochert) has increased over geological time. This study shows solid Earth cooling, not just seawater temperature changes, explains this trend.
Area of Science:
- Geochemistry
- Paleoclimatology
- Geochronology
Background:
- The oxygen isotope ratio of cherts (δ18Ochert) shows a ~15‰ increase from the Archean to present.
- Two main hypotheses for this trend are cooling seawater temperature (TSW) and increasing seawater δ18O (δ18Osw), with no scientific consensus.
- Some researchers question the reliability of the δ18Ochert record due to potential alteration.
Purpose of the Study:
- To demonstrate that cherts are a reliable archive of diagenetic temperatures.
- To investigate the influence of silica diagenesis kinetics on quartz precipitation and δ18Ochert.
- To reconcile the δ18Ochert record with planetary cooling and other geological constraints.
Main Methods:
- Analysis of chert samples to assess diagenetic temperatures.
- Development of a diagenetic model incorporating heat flow through sediment columns.
- Reconstruction of seawater oxygen isotope budgets influenced by solid Earth cooling.
Main Results:
- Cherts robustly archive diagenetic temperatures, even after metamorphism and exposure to meteoric fluids.
- Silica diagenesis kinetics control quartz precipitation timing and temperature, influencing δ18Ochert.
- Decreased heat flow over geological time accounts for ~5‰ of the δ18Ochert increase, reducing the need for extreme TSW or δ18Osw reconstructions.
Conclusions:
- Solid Earth cooling over billion-year timescales is the primary driver of the monotonic δ18Ochert trend.
- This explanation is consistent with Precambrian glaciations, biological constraints, and the observed δ18Ochert trend.
- The study provides an internally consistent view of Earth's paleoceanographic and thermal evolution.
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