Constraining crustal silica on ancient Earth

Keller, C. Brenhin; Harrison, T. Mark

doi:10.1073/pnas.2009431117

Cited by 46 publications

(20 citation statements)

References 67 publications

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“…This view suggests a relatively late onset for plate tectonics during the Neoarchean, ∼ 2.5 Ga. However, recent analyses of the sedimentary trace element and titanium isotope record suggest instead evolved, silica-rich Archean continents (Greber et al 2017;Greber and Dauphas 2019;Keller and Harrison 2020;Ptáček et al 2020). This view suggests an earlier onset for plate tectonics during the Paleo-or Eoarchean, before 3.5 Ga.…”

Section: Introductionmentioning

confidence: 95%

The composition and weathering of the continents over geologic time

Lipp¹,

Shorttle²,

Sperling³

et al. 2020

Preprint

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The composition of continental crust records a history of construction by tectonics and destruction by physical and chemical erosion. Quantitative constraints on how both igneous addition and chemical weathering have modified the continents' bulk composition are essential for understanding the evolution of geodynamics and climate. We have extracted temporal trends in sediments' protolith composition and weathering intensity from the largest available compilation of sedimentary major-element compositions, of ~ 15,000 samples from 4.0 Ga to the present. To do this we used a new analytical method which inverts whole sedimentary compositions for protolith composition and weathering intensity simultaneously. We find that the average Archean upper continental crust was silica rich and had a similar compositional diversity to modern continents. This is consistent with an early-Archean, or earlier, onset of plate tectonics. In the Archean, chemical weathering was ~ 25 % more efficient at sequestering CO2 than in subsequent time periods. Since 2.0 Ga, over long (> 0.5 Ga) timescales, the crustal weathering intensity has remained largely constant. On shorter timescales over the Phanerozoic, the intensity of weathering is correlated to global climate state, consistent with silicate weathering feedback acting in response to changes in CO2 outgassing.

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Section: Introductionmentioning

confidence: 95%

The composition and weathering of the continents over geologic time

Lipp¹,

Shorttle²,

Sperling³

et al. 2020

Preprint

View full text Add to dashboard Cite

show abstract

“…Finally, we note that terrestrial scenarios face the possibility that while there was continental crust by at least 4 billion years ago [ 98 , 99 ] that the origin of emergent continental crust, that is terrestrial habitat, may have been as late as 3.5 billion years ago [ 98 , 100 ], but see [ 101 ], or even from 2.5 to 3 billion years ago [ 102 ]. However, others argue for terrestrial habitat much earlier [ 103 ]; similar to the study of the origin of life, understanding the early history of the Earth is also very difficult due to a lack of data, and there are still many points of disagreement [ 99 , 104 ].…”

Section: Evaluation Of Scenariosmentioning

confidence: 99%

‘Whole Organism’, Systems Biology, and Top-Down Criteria for Evaluating Scenarios for the Origin of Life

Brunk

Marshall

2021

Life

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While most advances in the study of the origin of life on Earth (OoLoE) are piecemeal, tested against the laws of chemistry and physics, ultimately the goal is to develop an overall scenario for life’s origin(s). However, the dimensionality of non-equilibrium chemical systems, from the range of possible boundary conditions and chemical interactions, renders the application of chemical and physical laws difficult. Here we outline a set of simple criteria for evaluating OoLoE scenarios. These include the need for containment, steady energy and material flows, and structured spatial heterogeneity from the outset. The Principle of Continuity, the fact that all life today was derived from first life, suggests favoring scenarios with fewer non-analog (not seen in life today) to analog (seen in life today) transitions in the inferred first biochemical pathways. Top-down data also indicate that a complex metabolism predated ribozymes and enzymes, and that full cellular autonomy and motility occurred post-LUCA. Using these criteria, we find the alkaline hydrothermal vent microchamber complex scenario with a late evolving exploitation of the natural occurring pH (or Na+ gradient) by ATP synthase the most compelling. However, there are as yet so many unknowns, we also advocate for the continued development of as many plausible scenarios as possible.

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“…2.5-4.0 Ga) continents are often viewed as having a mafic composition similar to the oceanic crust (e.g., Taylor and McLennan, 1986;Tang et al, 2016) suggesting a late onset for plate tectonics during the Neoarchean, ∼2.5 Ga. However, a contrasting view has emerged of evolved, silica-rich Archean continents (Greber et al, 2017;Keller and Harrison, 2020;Ptáček et al, 2020). This view suggests an earlier onset for plate tectonics before 3.5 Ga.…”

Section: Introductionmentioning

confidence: 99%

The composition and weathering of the continents over geologic time

Lipp¹,

Shorttle²,

Sperling³

et al. 2021

Geochem. Persp. Let.

View full text Add to dashboard Cite

The composition of continental crust records the balance between construction by tectonics and destruction by physical and chemical erosion. Quantitative constraints on how igneous addition and chemical weathering have modified the continents' bulk composition are essential for understanding the evolution of geodynamics and climate. Using novel data analytic techniques we have extracted temporal trends in sediments' protolith composition and weathering intensity from the largest available compilation of sedimentary major element compositions: ∼15,000 samples from 4.0 Ga to the present. We find that the average Archean upper continental crust was silica-rich and had a similar compositional diversity to modern continents. This is consistent with an early Archean, or earlier, onset of plate tectonics. In the Archean, chemical weathering sequestered ∼25 % more CO 2 per mass eroded for the same weathering intensity than in subsequent time periods, consistent with carbon mass balance despite higher Archean outgassing rates and more limited continental exposure. Since 2.0 Ga, over long (>0.5 Gyr) timescales, crustal weathering intensity has remained relatively constant. On shorter timescales over the Phanerozoic, weathering intensity is correlated to global climate state, consistent with a weathering feedback acting in response to changes in CO 2 sources or sinks.

show abstract

Constraining crustal silica on ancient Earth

Cited by 46 publications

References 67 publications

The composition and weathering of the continents over geologic time

The composition and weathering of the continents over geologic time

‘Whole Organism’, Systems Biology, and Top-Down Criteria for Evaluating Scenarios for the Origin of Life

The composition and weathering of the continents over geologic time

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