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dlw

The awesome mineral #lawsonite only forms in subduction zones, contains a lot of water, and is stable from shallow to great depths, so it is hugely important in the Earth’s water cycle. H2O in lawsonite—> melting—> volcanoes—> atmosphere + oceans —> and the cycle continues. It is a beautiful crystal ferry that helps make the Earth a habitable planet. #MinCup23

Barry Goldman

@dlw @silicatefondue

ok i was thinking about related topic the other day. the mantle is ~4000/2/3 =700 times the volume of earths oceans. mantle minerals ought to be able to incorporate water to make new minerals.

why is there an ocean at all?

its existence seems prearious.

did rock suck up the oceans on mars and venus or did they loose oceans to photolysis of H2O or both?

Sep 08, 2023, 02:32 PM·Public·Web
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Bill Minarik

@barrygoldman1 @dlw Both volcanism and metamorphism (mountain building) release water (and other volatiles) back into the atmosphere.

The balance of fluxes is very tricky to estimate accurately, and I'm not an expert on this.

Keavin Moore, a McGill student, is modelling how much water the interior of planets start with (0-D box model; physics favorite), and how it's recycled:
arxiv.org/abs/2308.00585
if you're interested. A thick atm can force a lot of water into the initially molten mantle.

arXiv.orgThe Role of Magma Oceans in Maintaining Surface Water on Rocky Planets Orbiting M-DwarfsEarth-like planets orbiting M-dwarf stars, M-Earths, are currently the best targets to search for signatures of life. Life as we know it requires water. The habitability of M-Earths is jeopardized by water loss to space: high flux from young M-dwarf stars can drive the loss of 3--20 Earth oceans from otherwise habitable planets. We develop a 0-D box model for Earth-mass terrestrial exoplanets, orbiting within the habitable zone, which tracks water loss to space and exchange between reservoirs during an early surface magma ocean phase and the longer deep-water cycling phase. A key feature is the duration of the surface magma ocean, assumed concurrent with the runaway greenhouse. This timescale can discriminate between desiccated planets, planets with desiccated mantles but substantial surface water, and planets with significant water sequestered in the mantle. A longer-lived surface magma ocean helps M-Earths retain water: dissolution of water in the magma provides a barrier against significant loss to space during the earliest, most active stage of the host M-dwarf, depending on the water saturation limit of the magma. Although a short-lived basal magma ocean can be beneficial to surface habitability, a long-lived basal magma ocean may sequester significant water in the mantle at the detriment of surface habitability. We find that magma oceans and deep-water cycling can maintain or recover habitable surface conditions on Earth-like planets at the inner edge of the habitable zone around late M-dwarf stars -- these planets would otherwise be desiccated if they form with less than ${\sim}$10 terrestrial oceans of water.
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Barry Goldman

@silicatefondue @dlw yes the balance could be tricky, but with SO MUCH MORE mantle than ocean... seems dangerous!

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