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A shorter Archean day-length biases interpretations of the early Earth's climate

Spalding, Christopher and Fischer, Woodward W. (2019) A shorter Archean day-length biases interpretations of the early Earth's climate. Earth and Planetary Science Letters, 514 . pp. 28-36. ISSN 0012-821X.

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Earth's earliest sedimentary record contains evidence that surface temperatures were similar to, or perhaps even warmer than modern. In contrast, standard Solar models suggest the Sun was 25% less luminous at this ancient epoch, implying a cold, frozen planet—all else kept equal. This discrepancy, known as the Faint Young Sun Paradox, remains unresolved. Most proposed solutions invoke high concentrations of greenhouse gases in the early atmosphere to offset for the fainter Sun, though current geological constraints are insufficient to verify or falsify these scenarios. In this work, we examined several simple mechanisms that involve the role played by Earth's spin rate, which was significantly faster during Archean time. This faster spin rate enhances the equator-to-pole temperature gradient, facilitating a warm equator, while maintaining cold poles. Results show that such an enhanced meridional gradient augments the meridional gradient in carbonate deposition, which biases the surviving geological record away from the global mean, toward warmer waters. Moreover, using simple atmospheric models, we found that the faster-spinning Earth was less sensitive to ice-albedo feedbacks, facilitating larger meridional temperature gradients before succumbing to global glaciation. We show that within the faster-spinning regime, the greenhouse warming required to generate an ice-free Earth can differ from that required to generate an Earth with permanent ice caps by the equivalent of 1–2 orders of magnitude of pCO_2. Accordingly, the resolution of the Faint Young Sun problem depends significantly on whether the early Earth was ever, or even at times, ice-free.

Item Type:Article
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URLURL TypeDescription
Spalding, Christopher0000-0001-9052-3400
Fischer, Woodward W.0000-0002-8836-3054
Additional Information:© 2019 Elsevier B.V. Received 23 August 2018, Revised 29 January 2019, Accepted 26 February 2019, Available online 18 March 2019. C.S thanks the generous support from the NESSF17R graduate fellowship, proposal number 17-PLANET17R-0014, and the Heising-Simons Foundation's 51 Pegasi b Postdoctoral Fellowship, grant number GR101980. W.F. acknowledges support from the Simons Foundation Collaboration on the Origins of Life. Additionally, we thank Konstantin Batygin, Greg Laughlin and Seth Finnegan for illuminating conversations.
Funding AgencyGrant Number
NASA Earth and Space Science Fellowship17-PLANET17R-0014
Heising-Simons FoundationGR101980
Subject Keywords:Archean; climate; Earth's rotation
Record Number:CaltechAUTHORS:20190318-122913562
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Official Citation:Christopher Spalding, Woodward W. Fischer, A shorter Archean day-length biases interpretations of the early Earth's climate, Earth and Planetary Science Letters, Volume 514, 2019, Pages 28-36, ISSN 0012-821X,
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:93922
Deposited By: Tony Diaz
Deposited On:18 Mar 2019 20:22
Last Modified:18 Mar 2019 20:22

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