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3 - The geochemical context and embedding of the biosphere

Published online by Cambridge University Press:  05 June 2016

Eric Smith
Affiliation:
Tokyo Institute of Technology
Harold J. Morowitz
Affiliation:
George Mason University, Virginia
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Summary

The chemical non-equilibrium order of life grows out of a much larger context of non-equilibrium order, occurring at scales from the formation of the Sun and planetary system, to the complex chemical environments and dynamics within the Earth's core and mantle, oceans, and atmosphere. Many disequilibria on Earth result from slow relaxation timescales in late-stage planet formation; with respect to these the Earth is still a “young” planet. These include partitioning of redox states of transition metals in the core, mantle, crust, and oceans; the slow process of partitioning of volatiles among the lithosphere, hydrosphere, and atmosphere; the escape of hydrogen and atmospheric photochemistry that move the atmosphere far from redox equilibrium with the mantle; and tectonic circulation below the crust, ocean circulation through it, and weather above it. Many of these disequilibria focus energy to an extreme degree on the rock/water interface and in the mixing chemistry of fluids and volatiles in and near the crust. Complex processes of crust formation at spreading centers drive fluid/rock interactions that both depend on and modify the chemistry of the oceans and atmosphere. Ecosystems supported by rock/water chemical disequilibria are the phylogenetically most basal and biochemically simplest, and in some ways the most conservative living systems on Earth. They have been put forth as models for the first life, and may serve as useful models if we are careful to recognize several key respects in which the Archean Earth was different from the Earth today. Here we first ask whether the same chemical stresses that support life today could have driven the emergence of the biosphere as a necessary planetary subsystem.

Order in the abiotic context for life

The order of life is inherently dynamical and dependent on forces and flows that keep living systems driven away from thermodynamic equilibrium. This fact was appreciated by Boltzmann in 1886, and has since been repeated sufficiently often [98, 570, 654, 711] to qualify as part of the common knowledge of the physics of living systems. However, to fully understand the non-equilibrium order of life it is necessary to recognize its context in a much larger field of non-equilibrium order that ranges in scope from the formation of the Sun and planetary systems, to the large-scale structure and energetics of the Earth, and down to complex webs of mechanism in planetary chemistry.

Type
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The Origin and Nature of Life on Earth
The Emergence of the Fourth Geosphere
, pp. 73 - 169
Publisher: Cambridge University Press
Print publication year: 2016

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